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TEKS 8.7 AThe Force is with You!
TAKS Objective 4 – The student will demonstrate an understanding of motion, forces, and energy.
Learned Science Concepts
Unbalanced forces cause changes in the speed or direction of an object’s motion.
Waves are generated and can travel through different media.
TEKS 8.7 Science conceptsThe student knows that there is a relationship between force and motion. The student is expected to:
(A) demonstrate how unbalanced forces cause changes in the speed or direction of an object's motion; and
OverviewThough motion and forces are observed and experienced everyday, few people have a clear understanding of the phenomena. In this section, students will develop an understanding of forces and motion by isolating and studying forces one at a time. Initially friction will be removed and an impulse force added. Next a constant frictional force due to air resistance will be observed as an object undergoes deceleration. Balanced forces will be observed as a falling object experiences the forces of gravity and air resistance.Frictional forces on a leaning ladder will be measured to determine how angle of the ladder, surface friction, and the placement of forces affect the stability of a ladder. The force of gravity on an object sliding frictionless down an inclined plane will be observed. Finally motion in the horizontal and vertical planes will be analyzed to confirm that
projectile motion is constant in the horizontal plane and accelerated due to gravitational force in the vertical plane.
Instructional StrategiesHands-on activities will involve discovery, inquiry, and experimentation. The activities scaffold learning concepts to strengthen concepts of force and motion. Students will begin studying linear motion in a nearly frictionless environment. They will apply a force and measure results. They will next look and unseen forces due to air resistance. Finally they will use the concept of air resistance to study and explain terminal speed in a freefall. A second series of exercises will allow students to study two-dimensional motion where one direction experiences the constant force of gravity. Counterintuitive ideas will be used to dispel deep-set misconceptions of motion.
Objectives1. The learner will apply the laws of motion to real world examples.
2. The learner will identify size and direction of a force.
3. The learner will determine if motion is constant or accelerated.
4. The learner will use equipment to measure time and distance so that the motion of the object can be determined.
5. The learner will used data collected to calculate the speed of an object.
6. The learner will explain the results of applying a force to an object.
For Teacher’s Eyes OnlyConcepts & VocabularyMotion- change in position
Speed- rate of motion = distance / timeDirection of Motion- where object is going- draw a straight line to represent where object was then & nowForce – a push or pull
Equilibrium- all forces balancedFriction- force when two surfaces touch- always in opposite direction of motion (Newton’s 3rd Law)Velocity – the speed and direction of an object.
Acceleration – a change in either the speed or the direction of an object.Work – force acting upon an object multiplied by the distance the object moves.
Newton’s 1 st Law
An object in motion stays in motion in a straight line, unless acted upon by unbalanced force- a push/pull will cause object to speed up, slow down or change direction
Newton’s 2 nd Law
Force = mass X acceleration- To explore acceleration, rearrange formula to show
Acceleration = force / mass-- Greater force = greater change in speed/direction
– Greater mass = smaller change in speed/direction– The change in direction always the same as the direction of the force– Longer time force applied = greater change is speed/direction
Newton’s 3 rd Law
Equal and opposite reactions
– You push DOWN on floor, floor pushes UP on you
– Steam out of bottom of space shuttle pushes down on launch pad, launch pad pushes up on space shuttle
Two Types of Motion- that 8th graders will study
1 dimensional motion
– Moving left & right OR up & down
2 dimensional motion
– Moving left to right AND up & down
– Projectile motion is a free fall with horizontal speed
If one really understands Newton’s three laws of motion, no matter what words one uses to articulate them, then much of the ways things move become clear. Otherwise, the world can be a bewildering place in which objects move in seemingly bizarre ways. It is imperative that the student be led to observe and to analyze the way things actually move. The “Laws” of motion are laws only in the sense that they are rules that describe what actually is happening when an object moves. Isaac Newton, about three hundred and twenty years ago (1687), was able to summarize all the essential knowledge of motion in three fundamental rules: Newton’s Laws of Motion.Newton’s First Law of Motion (Xtreem Science version):An unbalanced external force (and only such a force) is what causes an object to speed up, to slow down or to change its direction of motion (that is, accelerate).Some consequences of this rule are:
The motion is an overall motion of the object rather than the motion of one part relative to another part.
If an object (which must be made of matter to be an object) is motionless to begin with, then it will continue to be motionless (“will remain at rest” as physicists say) indefinitely unless or until it is acted on by an unbalanced external force.
A body that is moving will continue to move in a straight line at the same speed unless or until an unbalanced external force acts on the object.
If an object is speeding up, slowing down and/or changing the direction of its motion an unbalanced external force is exerting itself on the object.
“Acceleration,” as physicists use the word, means that there is a change in the speed (increase or decrease) and/or a change in the direction of motion.
Newton’s Second Law of Motion takes the first Law one step further. The Second Law gives the arithmetic relationship between the acceleration, the force and the mass of an object.The acceleration is precisely the rate of change in the speed and/or direction, that is, it is equal to the change in the speed or direction divided by the time it takes to make the change.In an equation:
Acceleration = change in speed or direction / time to make the changeThus, if an object has a large acceleration, its motion is changing rapidly, while—on the other hand—if the motion is changing slowly the acceleration is small. If the motion of the object is not changing at all, the acceleration is exactly equal to zero, no matter what the speed or direction of the motion. Newton’s Second Law connects the size of the force, the mass or amount of material in the object and the acceleration that the object experiences.Newton’s Second Law of Motion (Xtreem Science version):The acceleration of the overall motion of an object that is subjected to an unbalanced external force is equal to that force divided by the mass of the object.In an equation:Acceleration = Force / massThe concept of acceleration is fundamental to the understanding of motion. A force produces acceleration. Force is measured in the metric system in units of Newtons, appropriately named for Sir Isaac Newton. One Newton force (symbol N) is approximately equal to the weight of a small apple. The weigh of about $1 worth of nickels (20) is also a force just slightly less than 1.0 N. Stretch a 1/8 inch x three inch rubber band to a length of about six inches and it pulls back with a force about 5 Newtons. In the English system the unit of force is the pound (lb), but this is a confusing measure because we also talk about the mass or the amount of material of an object in pounds. (There is a very inelegant and little used unit of mass in the English system, know as the “slug.” It weighs about 32 pounds.) In the metric system a different unit is used for the mass or amount of material rather than the unit of force; the unit of mass is the kilogram (1 kg =1000 gram). One liter of water has a mass of very nearly 1 kg. One nickel has a mass of about 5.0 grams or 0.005 kg. Thus, 200 nickels ($10) have a mass of very close to 1 kg. Weight, on the other hand, is the force of the attraction the earth’s mass has on the mass of the object. Near sea level, a mass of 1 kg weighs (is attracted to the earth with a force of) 9.8 N. In deep space, very far from earth, 1 kg has no weight at all but still has a mass of 1 kg.Qualitative and semi-quantitative consequences of the Second Law:
The greater the force that is applied to an object, the greater will be the rate of change in the speed or direction of its overall motion.
The greater the mass an object has, the smaller will be the rate of change in the speed or direction of motion. (Recall a =F/m or Fm) Thus, we say that the more massive object has more “inertia.”
The change in the speed or direction of motion is always in the direction of the unbalanced external force. If an object is thrown up into the air, the change in the up-and-down speed is always directed downward. On the way up the speed gets less (a downward change). On the way down the speed increases (also a downward change). This is because the force (weight) is always toward the earth.
The longer time that a force is applied to an object, the larger will be the total change in its speed and/or the direction of its motion.
The final law of motion seems subtle but is very much just common sense. Newton’s Third Law of Motion (Xtreem Science version)
If an object pushes (or pulls) on another object, the second object pushes (or pulls) back on the first object with a force exactly equal in size but exactly opposite in direction.Consequences of this Law are far reaching:
Internal forces always balance and, therefore, produce no effect on the overall motion.
You cannot actually “pull yourself up by your boot straps” because pulling on your bootstraps causes them to pull back with the same and opposite force; so the net effect is balanced.
In collisions one object pushes on the other object with a force equal in size but opposite in direction to the first.
All forces acting on material objects originate from other material objects, even if they are far apart. There is no pushing against or pulling on nothing.
Rockets, jet engines or jet skis are so-called impulse engines and work by greatly accelerating a fluid (gas or liquid) out the back. The force applied to the fluid by the engine to make the fluid go faster produces a like-sized force on the engine in the opposite direction that propels the engine forward. Motion is not the result of the gases pushing against the air.
All motion can be understood by these three simple rules: Newton’s Laws of Motion. However, they must be applied to particular situations with full attention to identifying all the forces and the masses involved.
Student Misconceptions Misconception
A force is necessary to keep a body moving.
Science ConceptIn fact, the opposite is true. It is often the contrary force of friction that causes objects to slow down and eventually stop. If no force is exerted on a body then it will continue to move as it did before.
Rebuild ConceptShow an object in motion in (nearly) frictionless condition. Let students discuss or experiment with keeping the object in motion (add no force) and stopping the object (apply a force).
MisconceptionIf an object is sitting still (is at rest) there are no forces acting on it.
Science ConceptThe statement is almost right: if an object is at rest there are no unbalanced external forces acting on. There can be very many and very large forces acting on an object sitting still, but they all balance out.
Rebuild ConceptConsider a very large balancing boulder. The rock is sitting still but the weight of the rock is pushing very hard on the rock underneath it. Meanwhile, the rock underneath is pushing back up with exactly the same force and in the opposite direction, so the forces, even though they are very large, are balanced out. If the rock beneath fails to provide the balancing force, then the balancing boulder becomes a rolling stone.
MisconceptionThe influence of a force continues to be felt even if the force is not acting on the object.
Science ConceptThe speed and/or the direction of the overall motion of an object change when and only as long as a force exerts itself on the object. When the force is “turned on” the body speeds up, slows down and/or changes direction. When the force is “turned off” the object will continue to go in the same direction and at the same speed as it was going the instant when the force was removed.
Rebuild ConceptDiscuss a spacecraft, ignoring gravity acting upon it. What happens when the rockets fire and don’t fire. This concept of motion should be brought up during many different motion activities because it is very hard to dispel the misconception.
Student Prior KnowledgeStudents should be able to describe the changes in position, direction, and speed that occur when a force acts on an object. (TEKS 6.8 A)) Students should also be able to measure an object’s change in motion and produce a graph from the data. (TEKS 6.8 (B)) Students should be able to demonstrate Newton’s first law of motion that an objects motion will remain unchanged until acted upon by a force. (TEKS 7.6 (B))
5 E’sPush Me, Pull Me, Watch Me Fall
EngageEngage 1
(Set up a scenario for the students to discuss.) Suppose you were in a flying saucer far from any planet. Your engine had roared to life back on the moon base and you have been speeding up, accelerating, for a week. You have set a course for Polaris, the North Star. Now that you are flying at thirteen million miles an hour (13,000,000 mph), you decide that it is time to turn off your engine. What is going to happen?What if our flying saucer were flying through air? Would we need to turn on the engine?
Engage 2
Show an action video and allow students to talk about how the cars jumped, the motorcycles flew, or other force/motion events depicted.
Engage 3
Show a cartoon action and ask students to explain what is wrong with the science of force and motion. An example would be running off a cliff, feet keeps moving but forward motion stops, then falls straight down.
Engage 4Demonstration: Come back can
The Come Back Can has a top and bottom. A rubber band is stretched and attached in two places on both the top and bottom with a weight attached at the middle of the rubber band. Roll the can, it will move forward, stop, and come back.
ExploreExploration 1
Activity: Dare you to stop meClass Time: 30 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.Materials
Air puckMeter stickStopwatch
Air Puck: use the “Hover Puck ™” (Shaper Image Model #EC500) to simulate the motion of a flying saucer flying far from any gravitational field. Students will experiment with straight line motion at a constant speed. The point is to remove as many forces upon the object as possible. The puck floats on a layer of air and thus most friction is eliminated.
7. Have students observe the motion of the puck traveling at two different speeds. (Launched with different force magnitudes)
8. Have students measure off one meter, two meters and three meters and time the how long the puck takes to cover each meter. One student should puck the puck, one student should time as it crosses 1m, another students times as it crosses 2m and another times as it crosses 3m. This way, only one initial force is given. On a level surface students will find it takes the same length of time to go each of the meter distances.
9. Have students prepare motion maps of the motion. A Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.
10. Have the students calculate the speed by dividing the distance the puck travels by the time it takes to travel that distance. s = d/t
11. Have the students plot the distance from the start versus elapsed time. Students may use a graphing calculator or spreadsheet program for creating a data chart and graph.
12. Have the students plot the speed versus time elapsed. Was the speed constant? Why or why not? What forces were acting on the puck? How does this compare to a ship in space?
Exploration 2
Activity Knocked off courseClass Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.
MaterialsAir puckRubber malletDigital camera or video camera
Kicked Air Puck: using the “Hover Puck” and a rubber mallet (a hard rubber ball taped to a meter stick will suffice) discover the effects on the motion of an otherwise un-accelerated object with a force applied over a short time.13. Set the puck in motion. Use a video camera or digital camera with video mode to
capture the motion of the puck. If possible take the video shot from above the action.
14. After the puck has traveled a meter or so, use the mallet to tap the puck. Don’t push the puck, give it a quick bump.
15. Repeat this several times whacking the puck in different directions at 90, 45, 120 and 180. Does the puck go in the exact direction of the force every time?
16. Now whack to puck at 90 but using small, medium, then large forces. Does the amount of force make a difference on the puck’s angle of motion?
17. Use the video to determine what affect the direction and size of the force had on the motion of the puck.
Explain
Question series: (Use some or all of the questions to guide student thoughts and help them construct knowledge. Insert questions as needed to keep this discussion going and reach a higher level of thinking)18. How does an object behave when there are no forces acting upon it? It will stay in one
spot or move at a constant speed in one direction.
19. When the puck was moving in activity one what force(s) were acting upon it? No forces were acting on it to keep it in motion. Gravity was a constant force that kept the puck on the ground but did not affect the straight line motion.
20. Why didn’t the puck move in a perfectly straight line? Inconsistencies in the floor or ground. Other answers could also be correct.
21. Why did the puck not move each equal distance in exactly the same time? Could be many reasons including: the reaction time of the persons with the stopwatches, the ground was not level, there was still some friction.
Summary: In a perfect situation, the puck would move forever in a straight line with exactly the same speed.
22. What is required to change the speed or direction of the puck? The application of a force on the puck.
23. Did the puck move in the direction of the applied force? Not necessarily. If the force were applied at 90o to the direction of motion of the puck, the puck would continue moving but at an angle somewhere between the original direction and the direction of the force. A larger force causes the motion to be more in the direction of the force.
Review the pictures or video of the pucks motion. When no force was added, the puck traveled in a straight line with a constant speed. When the puck was in motion and struck at right angles, the puck traveled off at an angle to the original direction and at an angle to the direction of the force. Depending on the size of the force, the angle to the original direction changes.
Motion: when an object changes its position; when it moves.
Speed: the rate at which an object moves; how far something moves divided by the time it takes to make the move.
Direction of Motion: where the object is moving. Draw a straight line from where the object was to where it is now.
Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.
Force: a push or pull.
Equilibrium: when all forces are balanced.
Balanced force: when all the forces are cancelled by other forces.Friction: the force that happens with two surfaces touch.Force diagram: a sketch that shows all the forces acting on an object.
ElaborateElaboration 1
Experiment Flag me downClass Time: 30 minutesObjective 1: The learner will identify size and direction of a force.
Objective 2: The learner will determine if motion is constant or accelerated.
Objective 3: The learner will explain the results of applying a force to an object.
Materials:Air puckPaper for a sailMasking tapeScissorsMeter stickStopwatch
Activity Overview One usually thinks about applying a force to an object such as the puck. In the Elaboration 1 the force will be applied to move the air as the puck moves. A sail will push the air along with the motion of the puck and the air will push back thus slowing the puck to a gradual stop.
Preparation Cut different sizes of sails from the paper. Attach a sail to the air puck using tape. The sail may be wrapped around the circumference of the puck. Since the sail is moving an area of air, the area of the sail should be measured.
In order to make sense of the results, the force applied to the puck must be the same each time. Brainstorm with the class ways in which the can be sure the force is very close to the same each trial.
1. Measure the size of your small sail and record.
2. Place the puck at a marked spot and apply a force (blow into the sail for a count of 5).
3. Let the puck travel until it stops.
4. Measure the distance and time the puck traveled. What was the direction and motion?
5. Measure the size of the large sail and record.
6. Replace the small sail with the larger sail and place the puck at the starting line. Apply the same force as in the first trial (blow into the sail for a count of 5).
7. Take the distance and time measurements.
Elaboration 2
Activity: Help me I’m fallingClass Time: 35 minutesObjective 1: The learner will determine if motion is constant or accelerated.
Objective 2: The learner will use equipment to measure time and distance so that the motion of the object can be determined.
Objective 3: The learner will explain the results of applying a force to an object.
MaterialsTightly woven light weight cloth or plastic sheetCup and weights and stringMeter stickDigital camera to make movie of eventStopwatch
Activity Overview: In the activity for Elaboration 2 students will explore the action of force on an object using parachutes. A parachute works by pushing on the air to make it
accelerate. Air has mass. A box of air one meter (about a yard) on a side has a mass of about 1.2 kg (equivalent to the mass of a partially drunk 2 liter bottle of pop). After a little reflection you can see that the larger the area of the parachute the larger will be the volume and, therefore the mass, of the air that is caught up by the fabric. If the parachute is moving at a certain speed, then the air that is caught must be accelerated to that speed. Moreover, the faster the parachute is moving the more mass of air per second will be caught by it. Therefore, the force that the parachute must exert on the air is proportional to the square of the speed of the parachute. In addition, if the parachute exerts a force on the air to get it to move faster, the air exerts a backward force of equal size on the parachute. Equation: Drag Force = Constant x Area x speed 2. The students must measure the constant, which will depend on the shape of the parachute.
Thus, when we drop a parachute with a mass attached, it will accelerate until the speed of the parachute through the air produces an upward force on it that is equal to the downward pull of gravity. When the forces balance the parachute continues to fall but at a constant speed and direction. The parachute has reached its “terminal velocity.” If we add more weight to the parachute it will fall faster because the air must move past the parachute at a higher speed to produce a force equal to a larger weight. On the other hand we can increase the area of the parachute to increase the amount of air that is being accelerated by the parachute and thereby increase the force produced on the parachute for the same air speed.
The force produced on a parachute is analogous to the force produced on a diver who jumps into water only water is much denser, about 800 times denser. When the diver hits the surface of the water he must accelerate some of the water to his speed. The force required to make the water accelerate can be very large, especially if a large mass of water is involved as when the diver does a “belly flop.” Aerodynamic shapes reduce the drag effects of air and water by pushing the fluid aside without accelerating it to the speed of the object. Therefore, less force is required and less force is exerted by the fluid on the object moving through it.
Procedure
1. Design and build parachutes of several different sizes.
2. Drop the parachutes from a height of 2 meters or more.
3. Time or videotape the parachutes as they fall past each meter mark.
4. Determine if the parachute is accelerating as it falls or falling at a constant velocity (terminal velocity).
5. Discuss why the parachute stops accelerating even though the constant force due to gravity is being applied. The parachute pushes the air down and the air pushes back with the same force. When the force of the air pushing up on the parachute is equal to the force of gravity pulling down on the parachute, the forces are balanced and there is no acceleration.
EvaluateBring video examples of extreme sports force and motion. It could be Olympics events, scenes from movies involving cars, boats, planes, parachutes, snowboarding, etc. Have each student discuss in writing or with diagrams, what is happening with force, velocity, acceleration, and direction of motion. As an alternative, students may want to describe something they have seen in real life, on television, or in the movies. Check that students understand forces and consequences. Also check the students for proper use of the key vocabulary.
Dare You to Stop Me
Class Time: 30 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.Materials
Air puckMeter stickStopwatch
Air Puck: use the “Hover Puck ™” (Shaper Image Model #EC500) to simulate the motion of a flying saucer flying far from any gravitational field. Students will experiment with straight line motion at a constant speed. The point is to remove as many forces upon the object as possible. The puck floats on a layer of air and thus most friction is eliminated.
1. Have students observe the motion of the puck traveling at two different speeds. (Launched with different force magnitudes)
2. Have students measure off one meter, two meters and three meters and time the how long the puck takes to cover each meter. One student should puck the puck, one student should time as it crosses 1m, another students times as it crosses 2m and another times as it crosses 3m. This way, only one initial force is given. On a level surface students will find it takes the same length of time to go each of the meter distances.
3. Have students prepare motion maps of the motion. A Motion map: a drawing of the object showing where it is at different times; a “multiple exposures” drawing.
4. Have the students calculate the speed by dividing the distance the puck travels by the time it takes to travel that distance. s = d/t
5. Have the students plot the distance from the start versus elapsed time. Students may use a graphing calculator or spreadsheet program for creating a data chart and graph.
6. Have the students plot the speed versus time elapsed. Was the speed constant? Why or why not? What forces were acting on the puck? How does this compare to a ship in space?
DARE YOU TO STOP ME CLASS DATA TABLE
Speed at . . . (m/s)
Group # 1m 2m 3m
1
2
3
4
5
6
7
8
Class Average
1. How does an object behave when there are no forces acting upon it?
2. When the puck was moving in activity one what force(s) were acting upon it?
3. Why didn’t the puck move in a perfectly straight line?
4. Why did the puck not move each equal distance in exactly the same time?
5. Graph distance on y-axis, time on x-axis = speed
6. Graph speed on y-axis, time on x-axis = acceleration
Knocked off Course
Class Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.Materials:
Air puckRubber malletDigital camera or video camera
Kicked Air Puck: using the “Hover Puck” and a rubber mallet (a hard rubber ball taped to a meter stick will suffice) discover the effects on the motion of an otherwise un-accelerated object with a force applied over a short time.
1. Set the puck in motion. Use a video camera or digital camera with video mode to capture the motion of the puck. If possible take the video shot from above the action.
2. After the puck has traveled a meter or so, use the mallet to tap the puck. Don’t push the puck, give it a quick bump.
3. Repeat this several times whacking the puck in different directions at 90, 45, 120 and 180. Does the puck go in the exact direction of the force every time?
4. Now whack to puck at 90 but using small, medium, then large forces. Does the amount of force make a difference on the puck’s angle of motion?
5. Use the video to determine what affect the direction and size of the force had on the motion of the puck.
Force Angle Observations
45
90
120
180
1. What is required to change the speed or direction of the puck?
2. Did the puck move in the direction of the applied force?
Flag Me Down
Class Time: 30 minutesObjective 1: The learner will identify size and direction of a force.Objective 2: The learner will determine if motion is constant or accelerated.Objective 3: The learner will explain the results of applying a force to an object.Materials:
Air puckPaper for a sailMasking tapeScissorsMeter stickStopwatch
Activity Overview One usually thinks about applying a force to an object such as the puck. In the Elaboration 1 the force will be applied to move the air as the puck moves. A sail will push the air along with the motion of the puck and the air will push back thus slowing the puck to a gradual stop.
Preparation Cut different sizes of sails from the paper. Attach a sail to the air puck using tape. The sail may be wrapped around the circumference of the puck. Since the sail is moving an area of air, the area of the sail should be measured.
1. In order to make sense of the results, the force applied to the puck must be the same each time. Brainstorm with the class ways in which the can be sure the force is very close to the same each trial.
2. Measure the size of your small sail and record.
3. Place the puck at a marked spot and apply a force (blow into the sail for a count of 5).
4. Let the puck travel until it stops.
5. Measure the distance and time the puck traveled. What was the direction and motion?
6. Measure the size of the large sail and record.
7. Replace the small sail with the larger sail and place the puck at the starting line. Apply the same force as in the first trial (blow into the sail for a count of 5).
8. Take the distance and time measurements.
Size of Sail Distance (m) Time (sec) Speed (s=d/t)
Small
___cm X ___cm
Large
___cm X ___cm
1. Calculate the speed of the puck with the small sail and large sail using the formula speed = distance / time. Record in table.
2. Add your calculated speeds to the class data table.
3. Which sail increased the speed of your puck? Why?
4. Which sail decreased the speed of your puck? Why?
Help Me! I’m Falling!
Class Time: 35 minutesObjective 1: The learner will determine if motion is constant or accelerated.Objective 2: The learner will use equipment to measure time and distance so that the motion of the object can be determined.Objective 3: The learner will explain the results of applying a force to an object.Materials
Tightly woven light weight cloth or plastic sheetCup and weights and stringMeter stickDigital camera to make movie of eventColored masking tapeStopwatch
Teacher PrepOn the wall of the “drop zone” use the colored masking tape to mark 1m increments for the length of the drop. The marks need to be show up against the wall when filmed.
Procedure1. Design and build parachutes of two different sizes.
2. Drop the parachutes from a height of 2 meters or more. Make sure the bottom of the cup is even with the taped mark.
3. Time or videotape the parachutes as they fall past each meter mark.
Distance Time Speed (s=d/t)
Small parachute
Large parachute
4. Calculate the speed of the small parachute and large parachutes using the formula speed = distance / time. Record in table above.
5. Add your data to the class table, “class Results for Speed of Parachute.”
Class Results for Speed of Parachute
Speed of Parachute
Group # Small Parachute (m/s) Large parachute (m/s)
1
2
3
4
5
6
7
8
Average speed
6. What is the relationship between parachute size and speed?
Extension
1. Review your parachute falling on video.
2. Record distance at time at 1m intervals. Calculate speed using the formula speed = distance / time and record.
SMALL PARACHUTE Time (sec) Speed (m/s)
Distance
1m
2m
3m
4m
LARGE PARACHUTE Time (sec) Speed (m/s)
Distance
1m
2m
3m
4m
3. Record your speeds in the table below.
Speed at . . . (m/s)
1m 2m 3m 4m
Small parachute
Large parachute
4. Does the speed stay constant during the entire drop?
5. At any point does the speed stop changing?
6. What vocabulary word means “a change in speed or direction”?
7. Why does the parachute stop accelerating?
Ladder Rip
EngageIn the previous activities a hover puck was used to eliminate friction. Pose the following question to the class: Is friction a good thing, or a bad thing? Allow discussion for a minute or two or until someone says “It depends.” Respond with “Depends upon what?” Without comment begin the Explore activity.
ExploreActivity: Friction can slow things downClass Time: 30 minutesObjective: The learner will explain the results of applying a force to an object.
Objective: The learner will identify size and direction of a force.
Materials(One per group)An object with a flat bottom such as a box or brickSpring scale
Procedure:
1. Attach the spring scale to the dragging object so that it can be pulled with a horizontal force. Ask students why it is important that the force be horizontal to the surface. So as to measure the force due to dragging (overcoming friction) and not measure the weight of the object.
2. Drag the object at a constant speed. Ask student why it is important that the speed be constant. If more force than that to oppose friction were used, the object would accelerate. By pulling at a constant speed, the experiment can be sure that the measured force is equal and opposite of the frictional force.
3. Drag the object across several different surfaces and measure the force as in step 2. Keep the data, including surface and force, in a student laboratory log book.
ExplainFriction is a force involved in every motion of an object. Whether it is a spinning flywheel, walking across the floor, or a flying bird, friction plays a part. Sometimes friction is a good thing. For example, it is much easier to walk across dry concrete than walk across ice. Sometimes friction must be overcome. For example, a skateboard is much more fun if the wheels move freely with little friction.What direction does friction act? It acts opposite to the direction of motion.Draw a force diagram.
The two arrows are the same size representing the force being the same magnitude. The two arrows are in opposite directions. This means there are no net forces and the object is not accelerating. Is the object moving? It may be moving at a constant speed or it may be accelerating.In the Elaboration activity students will study friction from a surfaces upon which a ladder is placed. The angle at which a ladder is leaned against a wall is crucial for safety. A seemingly well placed ladder can slip when climbing the rungs if the angle is wrong.
ElaborateActivity: Lean your ladder carefullyClass Time: 30 minutesObjective: The learner will apply the laws of motion to real world examples.
MaterialsModel ladderGlass surface, wood surface, sand-paper surfaceNewton force scale
Procedure: 4. Lean a model ladder against two surfaces that are at right angles to each other.
Provide two glass-like slick surfaces, two wood surfaces and two sand-paper-covered surfaces.
5. Attach a small Newton force scale to the lower rung and gently pull out on the ladder record the force that moves the bottom out.
6. Attach the Newton scale to the top rung and try lifting. How much force does it take to lift the top of the ladder away from the “wall?”
7. Pull on the bottom of the ladder, slowly decreasing the angle with the horizontal. At what angle does the ladder fall down?
8. Repeat the experiment with different surface.
9. Propose a model of what is happening to explain your observations.
10. Draw a diagram of all the forces that are acting on the ladder as it leans against the wall.
EvaluateWrite a short description of what you did and what you observed. Describe your model and discuss how your model explains what you observed.
Friction Can Slow Things Down
Class Time: 30 minutesObjective: The learner will explain the results of applying a force to an object.
Objective: The learner will identify size and direction of a force.
Materials(One per group)An object with a flat bottom such as a box or brickSpring scale
Procedure:
1. Attach the spring scale to the dragging object so that it can be pulled with a horizontal force. Why it is important that the force be horizontal to the surface?
2. Drag the object at a constant speed. Why it is important that the speed be constant?
3. Drag the object across several different surfaces at a constant speed and measure the force. Record.
Type of Surface Force (N)
4. What is the relationship between the type of surface and the amount of force necessary to keep the object moving at a constant speed?
Lean Your Ladder Carefully
Class Time: 30 minutesObjective: The learner will apply the laws of motion to real world examples.
MaterialsModel laddersmooth surface, paper surface, sand-paper surfaceNewton force scale
Teacher PrepSuggestion: acquire large smooth-glazed ceramic tiles to use in place of glass. Tape construction paper to the tiles for your “medium” surface and sand-paper for your rough surface.
Procedure: 1. Lean a model ladder against two surfaces that are at right angles to each other. Provide two glass-
like slick surfaces, two wood surfaces and two sand-paper-covered surfaces.
2. Attach a small Newton force scale to the lower rung and gently pull out on the ladder record the force that moves the bottom out.
3. Attach the Newton scale to the top rung and try lifting. How much force does it take to lift the top of the ladder away from the “wall?”
4. Pull on the bottom of the ladder, slowly decreasing the angle with the horizontal. At what angle does the ladder fall down?
5. Repeat the experiment with different surface.
6. Which surface has the greatest amount of friction? How can you tell?
7. State the relationship between the amount of friction and the amount of force needed to cause motion.
8. Draw a diagram of all the forces that are acting on the ladder as it leans against the wall.
Type of Surface Force to pull bottom rung (N)
Force to pull top rung (N)
Angle ladder falls ()
Smooth
Medium
Rough
The Gravity of the Situation
EngagePlace a coin on a meter stick. Slowly raise one end of the meter stick until the coin slides down it. Ask the students what happened. Let students respond without commenting to the correctness of their answers. If either the word friction or the word gravity is mentioned, question further to find out how much they understand about gravity and friction on an inclined plane.
ExploreActivity: Slipping and SlidingClass Time: 10 minutesObjective: The learner will explain the results of applying a force to an object.
MaterialsA board for an inclined planeHover puck
Procedure: 1. Put the puck on plane inclined at a small angle and allow the puck to slide down
the plane.
2. Increase the angle of the incline and slide the puck down again.
3. Increase the angle again and slide the puck down.
4. Record and explain the results.
Explain
Questions:
1. What happened when the angle of the inclined plane increased? The puck moved faster.
2. What force(s) are acting on the puck? Gravity
3. If gravity is constant, why does raising the incline cause the puck to move faster? At small angles, there is a lot of horizontal force. As the angle of incline gets closer to 90, the more gravity “takes over”-- the horizontal force decreases, allowing the puck to fall towards the ground.
Gravity
GravityNormal
Normal
Force down incline
Force down incline
ElaborateElaboration One
Activity: Zoom ZoomClass Time: 45 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.
Objective: The learner will used data collected to calculate the speed of an object.
Objective: The learner will explain the results of applying a force to an object.
Materials:Board for inclined planeHover puckStopwatchMeter stickProtractor for measuring the angle of the inclineGraph paper
Procedure: Design and perform an experiment to compare the angle of the incline with the average speed of the puck down the incline. Graph the average speed and angle of the incline.
Elaboration Two
Activity: It takes WorkClass Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.
Materials:Hover PuckInclined planeMeter stickCalculatorGraph paper (or electronic graph)Triple beam balance or other mass scaleSpring scale
Procedure:1. Measure and record the mass of the Hover Puck.
2. Place the Hover puck on the plane inclined at an angle (say 20 degrees). Attach the spring scale to the puck, turn it on and hold it steady on the incline so that it does not glide down. Record the force measured on the spring scale. Let the puck travel down the incline and measure the distance down the incline (only the incline) it traveled.
3. Repeat step 2 changing the angle each time. Angles of 20, 40, 60, and 80 degrees (or any other angles of choice) would be satisfactory.
4. Calculate the work involved in moving the puck down the incline. Work equals force (measurement of the spring scale) times distance (down the incline).
5. Calculate the acceleration of the puck. Force equals mass times acceleration (F = m*a). So the acceleration is equal to the force (as measured by the spring scale) divided by the mass of the puck.
6. Determine the acceleration due to gravity. Plot the acceleration determined at each angle. Predict what the acceleration at 90 degrees would be. This would be the acceleration due to gravity. The accepted value is 9.8 m/s2 but do not focus this activity on getting the “right answer”. Focus on procedure and prediction.
Evaluate
Each student will examine the data from their graphs and write a conclusion about how gravity affects an object sliding down an incline. Compare the graph and summary and score according to the correlation of the graph to the conclusion. Also look for insight and understanding and usage of correct terminology.
Score1. The conclusion and graph had some correlation.2. The graph was well done and the conclusion satisfactory.3. The graph and conclusion were well done.4. The graph and conclusion were well done with correct usage of vocabulary
and terminology.5. A great insight into the phenomenon was demonstrated in the conclusion.
Slipping and Sliding
Class Time: 10 minutesObjective: The learner will explain the results of applying a force to an object.
Materials:A board for an inclined planeHover puck
Procedure: 1. Put the puck on plane inclined at a small angle and allow the puck to slide down
the plane.
2. Increase the angle of the incline and slide the puck down again.
3. Increase the angle again and slide the puck down.
4. Draw two of your set-ups.
5. What happened when the angle of the inclined plane increased?
6. State the relationship between the angle of the inclined plane and the speed of your object:
7. What force(s) are acting on the puck?
8. If gravity is constant, why does raising the incline cause the puck to move faster?
Zoom Zoom
Class Time: 45 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.
Objective: The learner will used data collected to calculate the speed of an object.
Objective: The learner will explain the results of applying a force to an object.
Materials:Board for inclined planeHover puckStopwatchMeter stickProtractor for measuring the angle of the inclineGraph paper
Procedure: 1. Design and perform an experiment to compare the angle of the incline with the
average speed of the puck down the incline. 2. Distance = length of the board ________m3. Graph the average speed on the Y axis and angle of the incline on the X axis.4. State the relationship between the angle of incline and the speed of your object:
Angles () Time (sec) Calculated Speed (m/s)s = d/t
It Takes Work
Class Time: 20 minutesObjective: The learner will explain the results of applying a force to an object.
Materials:Hover PuckInclined planeMeter stickCalculatorGraph paper (or electronic graph)Triple beam balance or other mass scaleSpring scale
Procedure:1. Measure and record the mass of the Hover Puck.
2. Place the Hover puck on the plane inclined at a 20 angle. Attach the spring scale to the puck, turn it on and hold it steady on the incline so that it does not glide down. Record the force measured on the spring scale.
3. Let the puck travel down the incline and measure the distance down the incline (only the incline) it traveled.
4. Repeat steps 2 and 3, changing the angle each time. Record the results for angles of 20°, 40°, 60°, and 80°.
5. Calculate the work involved in moving the puck down the incline. Work equals force (measurement of the spring scale) times distance (down the incline). W = f X d.
6. Calculate the acceleration of the puck. Force equals mass times acceleration (F = m*a). So the acceleration is equal to the force (as measured by the spring scale) divided by the mass of the puck. a = f / m.
7. Graph the acceleration determined at each angle (acceleration on the Y axis, angles on the X axis.
8. Based on your graph, predict what the acceleration at 90 degrees would be. This would be the acceleration due to gravity.
Mass of hoverpuck _________grams
Angles Distance (m)
Force (N) Work (m-N) Acceleration (N/g)
20
40
60
80
Right between the Goal Posts
EngageTell the following classic story of the monkey and the hunter.One day a hunter was out in the woods. A thousand yards away in a tree he saw a monkey about 100 feet in the air hanging from a branch. Slowly he raised his gun and pointed the barrel of the gun directly at the monkey. Just as the hunter pulled the trigger on his gun, the monkey saw the hunter and let go of the branch. On the way down the monkey could be heard to say, “I shouldn’t of had ought to have done that.” Did the hunter’s bullet or the impact of the fall kill the monkey?Allow for discussion. Answer: The bullet. If the monkey had continued to hang on the branch, the bullet would have whizzed below the monkey.The activities in the Explore and Elaborate sections are designed build an understanding of why the monkey was hit by the badly aimed bullet.
ExploreActivity: Flying Football ForcesClass Time: 20 minutesObjective: The learner will determine if motion is constant or accelerated.
Materials:Paper for making footballsDigital camera for taking a short movieRuler
Procedure:1. Fold an 8.5 x 11 inches paper into a flag fold resulting in a triangular shaped football.
(See diagram) Fold paper on the dashed lines. On Step 3 fold the leftover flap into the previous fold.
2. Set up the camera so it can capture the flight of the football from the desktop to the floor.
3. Start the movie capture and launch the football using a pencil as a flicker or flick with the fingers.
4. Project the video or show it through a TV monitor.
5. Move the movie forward frame by frame. On each frame measure the distance of the football from the edge of the desk and the distance from the floor. Record the data.
6. Discuss how the horizontal distances compare. Discuss how the vertical distances compare.
ExplainThe Explore activity shows a combination of two forces, one force applied horizontally at launch and the other constant force downward due to gravity. This results in a curved path combining horizontal and vertical motions.
Questions:
1. What force(s) acted upon the football when it was in midair? Only gravity
2. What evidence indicates there was no horizontal force acting on the football in midair? The horizontal motion of the football was constant or in other words the football moved with a constant speed and direction.
Step 1 Step 2 Step 3
Step 4
3. What evidence indicates there was a vertical force downward on the football in midair? The speed of the football increased as the football fell. In other words the football accelerated in a downward direction.
4. How does the flight of the football confirm Newton’s Laws of Motion? The Law of Inertia says that motion of the football will be constant without a net force upon it. The motion is constant in the horizontal direction because there is no force acting upon the football in that direction. Newton’s Second Law says that when a net force is applied to the football it will be accelerated. The force of gravity was constant and the football accelerated downward in the direction of the force.
Now back to the monkey and the hunter. Every good hunter knows that the barrel of the gun should be aimed above the target to allow for the falling of the bullet as it travels from the gun to the target. If the monkey hung on to the branch, the bullet would not hit him. Since he let go of the branch, he fell at the same speed as the bullet fell. He fell during exactly the same time as the bullet because he let go just as the bullet left the gun. Presto, they both met at the same spot!
The next activities will confirm that objects fall with the same acceleration (disregarding the influence of air) despite their horizontal motion.
ElaborateElaboration One
Activity: I’m falling and I can’t get up.Class Time: 20 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.
MaterialsSeveral paper footballsDigital camera for recording motion
Procedure:Design and perform a procedure to show that footballs falling from the same height hit the ground at the same time regardless of how fast they move horizontally. Caution: flying objects can pose dangers. Make sure the flying footballs are pointed away from other people.
Write down the procedure and the results.
Elaboration Two
Activity: Three Points!Class Time: 30 minutesObjective: The learner will explain the results of applying a force to an object.
Materials:Paper footballBoard or book to make an inclineProtractor for measuring the angle of the incline
Procedure:1. Set up a target or mock goal posts.
2. Launch the football horizontally off the table and try to hit between the goal posts.
3. Move the goal posts farther from the table. Using the same force as in step two when the launch was successful, launch the football again horizontally.
4. Increase the force of the launch until the football successfully clears the goal posts.
5. Next launch the football at an upward angle using the book or board as a launching pad. When the football clears the goal posts, record the angle of the launch.
6. Move the goal posts farther from the table. Using the same force as step 5, launch the football at various angles until the goal posts are cleared.
7. Perform step 6 several more times.
8. Record observations and conclusions.
EvaluationAsk students to draw a diagram of the forces acting on a fly baseball and to explain their diagram in writing.
Flying Football Forces
Class Time: 20 minutesObjective: The learner will determine if motion is constant or accelerated.
Materials:Paper for making footballsDigital camera for taking a short movieRuler
Procedure:1. Fold an 8.5 x 11 inches paper into a flag fold resulting in a triangular shaped
football. (See diagram) Fold paper on the dashed lines. On Step 3 fold the leftover flap into the previous fold.
2. Set up the camera so it can capture the flight of the football from the desktop to the floor.
3. Start the movie. Launch the football using a pencil as a flicker.
4. Project the video or show it through a TV monitor.
5. Move the movie forward frame by frame. On each frame measure the distance of the football from the edge of the desk and the distance from the floor. Record the data.
6. How do the horizontal distances compare? How do the vertical distances compare?
Step 1 Step 2 Step 3
Step 4
I’m falling And I Can’t Get Up
Class Time: 20 minutesObjective: The learner will use equipment to measure time and distance so that the motion of the object can be determined.
Materials:Several paper footballsDigital camera for recording motion
Procedure:Design and perform a procedure to show that footballs falling from the same height hit the ground at the same time regardless of how fast they move horizontally. Caution: flying objects can pose dangers. Make sure the flying footballs are pointed away from other people.
Write down the procedure and the results.
Three Points!
Class Time: 30 minutesObjective: The learner will explain the results of applying a force to an object.
Materials:Paper footballBoard or book to make an inclineProtractor for measuring the angle of the incline
Procedure:1. Set up a target or mock goal posts in middle of table.
2. Launch the football horizontally off the table and try to hit between the goal posts.
3. Move the goal posts back 10 cm. Using the same force as in step two when the launch was successful, launch the football again horizontally. Did you make it?
4. Increase the force of the launch until the football successfully clears the goal posts.
5. Next launch the football at an upward angle using the book or as a launching pad. When the football clears the goal posts, record the angle of the launch.
6. Move the goal posts farther from the table. Using the same force as step 5, launch the football at various angles until the goal posts are cleared.
7. Perform step 6 several more times.
8. Record observations and conclusions.
9. State the relationship between the distance of the goal and the angle of launch:
Goal distance from launch pad Angle of launch pad
50cm
100cm
150cm
200cm
