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Teacher Notes

This power point has fill-in-the-blank notes pages that go along with it. See blackboard.


Warm-up # 40-forcesLook around the room and think about the objects

you see in terms of force. A force is always exerted by one object on another object.

Answer in complete sentences:A. Where do you see a force happening in the room

right now?B. Which object is exerting the force, and which is

receiving it?

Chapter 5 Section 2 What Is a Force?


Objectives

• Describe forces, and explain how forces act on objects.

• Determine the net force when more than one force is acting on an object.

• Compare balanced and unbalanced forces.

• Describe ways that unbalanced forces cause changes in motion.



Forces Acting on Objects

1. In science, a force is simply a push or a pull exerted on an object. All forces have both size and direction.

2. Any change in motion is caused by an unbalanced force.3. Scientists express force using a unit called the newton (N) and is measured with a spring scale.



Click below for animation on forces. http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/70310.htm

Forces.mht

This is from the online textbook. If it doesn’t work, go to the online edition, choose Ch. 5, choose the red tab-eactivities, click on forces to open. Choose file and save as. Save into the same folder as the power point. In the power point, choose insert, object, choose create from file, browse to find the file, and insert motion.You may need to hyperlink it back to the file. Contact [email protected] for help


4.Objects always have some kind of force acting on them

5. What are 2 examples of objects on which you exert a force when you are doing your school work?

6. What is an example of a force that does not

cause an object to move?Sitting on a chair, or writing on paper


• Unseen Sources and Receivers of Forces It is not always easy to tell what is exerting a force or what is receiving a force. •For example, you cannot see what exerts the force that pulls magnets to refrigerators. (magnetism) You cannot see that the air around you is held near Earth’s surface by a force called gravity.Air pressure also acts on objects and we can’t see it.


7. What is an example of an unseen source exerting a force?

The force that makes the cat’s hair move is called electromagnetism.


Determining Net Force

• Usually, more than one force is acting on an object. 8. The net force is the combination all of the forces acting on an object.

• Determining net force depends on the directions of the forces. To watch , double click on icon


Visual Conceptsnetforce.mht


• Forces in the Same Direction Two forces are added to determine the net force if the forces act in the same direction. The net force will be in the same direction as the individual forces.

• Forces in Different Directions If forces are acting in opposite directions, the net force can be found by subtracting the smaller force from the larger one.


9. How is net force determined if 2 students moving a

piano exert force in the same direction?

Now do #10 on your own



10. Use the picture to help answer the question.

11. What will knowing the net force on an object tell you

about the object? Motion and Direction


Balanced and Unbalanced Forces

12. Balanced Forces When the forces on an object produce a net force of 0 N, the forces are balanced.

There will be no change in motion. If the net force is 0 N then an object will either remain at rest or in motion.



Balanced and Unbalanced Forces, continued13. Unbalanced Forces When the net force on an object is not 0 N, the forces on the object are unbalanced.

• Unbalanced forces produce a change in motion, such as a change in speed or a change in direction. Unbalanced forces are necessary to cause a non-moving object to start moving, or to change the motion of moving objects.



Forces and motion 3minGo to discovery school and download video clips. Put them in the same folder as the power point and choose insert, then choose video from file. Drag the corners to the size you’d like. Contact me if help is [email protected]


Vectors show magnitude and direction, now complete the back of the notes page, finish for homework http://www.youtube.com/watch?v=A05n32Bl0aY


H.W.- H.W.-Study for your test which will be Wed., 11/14, Look at “eactivities” in online textbook.

Suppose you and a younger sister or brother are at a neighborhood pool. Your sister or brother asks why there are signs that say “NO RUNNING.” What would be your answer?

Don’t copy the question, write a complete sentence for your answer. The sign is there because...

Chapter 5-3 Section 3 Friction: A Force That Opposes Motion

Warm-up # 41


Objectives

• Explain why friction occurs.

• List the two types of friction,and give examples of each type.

• Explain how friction can be both harmful and helpful.

Chapter 5 Section 3 Friction: A Force That Opposes Motion


The Source of Friction

1. Friction is a force that opposes motion between two surfaces that are in contact.

2. A3. Friction occurs because the surface of any object is rough

Even surfaces that feel smooth are covered with microscopic hills and valleys.



Visual Concepts-friction.mht

click on icon.


• How does the roughness of surfaces that are touching affect the friction between them?4. the rougher the surface, the greater the friction


How does the amount of force exerted on a surface affect the motion?

5. the greater the force, the greater friction


Friction


The Source of Friction, continued

• The Effect of Force on Friction The amount of friction depends on the force pushing the surfaces together. If this force increases, the hills and valleys of the surfaces can come into closer contact.

• The close contact increases the friction between the surfaces. Objects that weigh less exert less downward force than objects that weigh more, as shown on the next slide.





The Source of Friction, continued

6. What are 2 ways friction can be increased? -increasing the force on an object while moving it (push down on sandpaper while moving it)

-adding rubber to the surface (bottom of shoes)

-make the surface rougher (add sand to an icy road)



Types of FrictionKinetic Friction The word kinetic means “moving.” So, kinetic friction is friction between moving surfaces.

• The amount of kinetic friction between two surfaces depends in part on how the surfaces move. Surfaces can slide past each other, or a surface can roll over another surface.•Static Friction- friction at rest


Visual Concepts types of friction.mht


Types of Friction, continued• Usually, the force of sliding kinetic friction is greater than the force of rolling kinetic friction. It is usually easier to move objects on wheels than to slide the objects along the floor, as shown below.



Types of Friction, continued

Static Friction When a force is applied to an object but does not cause the object to move, static friction occurs.

• The word static means “not moving.” The object does not move because the force of static friction balances the force applied.

• Static friction disappears as soon as an object starts moving, and then kinetic friction immediately occurs.




7. Kinetic friction-moving with force applied (ex. pushing a cart on wheels) Static Friction-not moving with force applied (ex. A box that won’t move when you push it)


Friction: Harmful and Helpful

• Without friction, a car’s tires could not push against the ground to move the car forward, and the brakes could not stop the car. Without friction, a car is useless.

• However, friction can also cause problems in a car. Friction between moving engine parts increases their temperature and causes the parts to wear down.

• Friction can be both harmful and helpful, so it may be necessary to decrease or increase friction.



Helpful friction


Friction: Harmful and Helpful, continued

• Some Ways to Reduce Friction One way to reduce friction is to use lubricants. Lubricants are substances that are applied to surfaces to reduce the friction between the surfaces.

• Some examples of common lubricants are motor oil, wax, and grease. Lubricants are usually liquids, but they can be solids or gases.



Friction: Harmful and Helpful, continued

• Friction can be reduced by switching from sliding kinetic friction to rolling kinetic friction. Ball bearings can be placed between wheels and axels to make it easier for wheels to turn by reducing friction.

• Another way to reduce friction is to make surfaces that rub against each other smoother.



K W LWhat do you know

about gravity?What do you want

to know about gravity?

What did you learn?

GRAVITY

H.W.-Study for your test which will be Wed, 11/14, Work on the Chapter 5 Review, Due Tues, 11/13.

Warm-up # 42 & 43-Complete the K & W on your handout.

E.Q. How are Mass and distance related to gravitational force between objects?

GPS- S8P4a. Recognize that every object exerts gravitational force on every other object and that the force depends on the mass and distance.


What is gravity? 2min


1. Astronauts bounce on the moon when they walk because the moon has less gravity than the Earth.


The Effects of Gravity on Matter

• 2. The force of attraction between objects that is due to their masses and distances is gravity.

•Gravity can change the motion of an object by changing its speed, direction, or both.

• All matter has mass. Therefore, all matter is affected by gravity and all objects experience an attraction toward all other objects.

• The mass of most objects is too small to cause a force large enough to move objects toward each other.


The Effects of Gravity on Matter, continued

• The Size of Earth’s Gravitational Force Compared with all objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large.

• You must apply forces to overcome the Earth’s gravitational force any time you lift objects or even parts of your body.•3. If the earth’s mass doubled without changing in size, your weight would: •Would your mass change?

Chapter 5 Section 4 Gravity: A Force of Attraction


Newton and the Study of Gravity

• The Core of an Idea Why do objects fall toward the Earth? What keeps the planets moving in the sky?


• In 1665, British scientist Sir Isaac Newton made the connection between these two questions when, as legend has it, he saw an apple falling from a tree.


Newton and the Study of Gravity, continued

• Newton knew that unbalanced forces are needed to change the motion of objects. He concluded that an unbalanced force on the apple made the apple fall.

• He also reasoned that an unbalanced force on the moon kept the moon moving around the Earth.

• He proposed that these two forces are actually the same force––gravity.



Newton and the Study of Gravity, continued

•Law of universal gravitation describes the relationships between gravitational force, mass, and distance.

• The law is called universal because it applies to all objects in the universe.

•4. all objects are attracted to each other by gravitational forces which depend on the mass and distance between them



• 5. The greater the mass of objects, the greater the force between them.

Gravitational force is greater when two objects are closer together.

6. As the distance between the objects increases gravitational force decreases




Weight as a Measure of Gravitational Force

• The Differences Between Weight and Mass Weight is related to mass, but they are not the same.

• Weight is a measure of the gravitational force on an object. Weight changes whenever gravitational force changes.

• Mass is the amount of matter in an object. An object’s mass does not change if gravitational force changes.





Weight as a Measure of Gravity, continued

• Units of Weight and Mass The SI unit of force is a newton (N). Gravity is a force, and weight is a measure of gravity. So, weight is also measured in newtons.

• The SI unit of mass is the kilogram (kg). Mass is often measured in grams (g) and milligrams (mg) as well.

• On Earth, a 100 g object weighs about 1 N.



7. Why are mass and weight often confused? because we call mass weight and they are

the same number with different units


••• •

•

••••

balancespring scaleamount of matter in an object

constant on Earth because the mass of the earth does not change

measured in kilograms

MassWeight

expressed in newtonsnever changes, constant on earth

remains the same when gravitational force changes

changes when gravitational force changes

on the moon, is 1/6 of that on Earth

measure of gravitational force exerted on an object


Concept Mapping

Chapter 5 Matter in Motion

Use the terms below to complete the Concept Mapping on the next slide.

speed

time

velocity

motion

acceleration


K W LWhat do you know about

gravity?

What do you want to know about gravity?

What did you learn?

GRAVITY

H.W.-Study for your test which will be Wed, 11/14, Finish the Chapter 5 Review, Due Tues, 11/13.

Warm-up # 43-Complete the L on the warmup.

C.W.- finish Ch. Review, Concept map on page 762

E.Q. How are Mass and distance related to gravitational force between objects?

GPS- S8P4a. Recognize that every object exerts gravitational force on every other object and that the force depends on the mass and distance.


H.W.-Test tomorrow, study!!!!!!Add to Ch. Review Draw and Complete the concept map. Use these words: speed, acceleration, force, velocity, direction, motion

C.W.- check Ch. Review,

is due to a

Motion

which causes

which is a change in

dependent on

force acceleration

velocity

speed

direction





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< BackNext >PreviewMain Teacher Notes This power point has fill-in-the-blank notes pages that go along with it. See blackboard