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Define the following termsA. WeightB. GravityC. Friction
S-33I can explain the relationship between weight, gravity, and friction
What does friction normally do to a moving object?
What would be different in the world if there was not friction?
S-25I can describe different kinds of force.
SPS8 Students will determine relationships among force, mass, and motion.
b. Apply Newton’s three Laws to everyday situations.
c. Relate falling objects to gravitational force.d. Explain the difference in mass and weight.
Chapter 12
Newton’s Laws
How do forces affect the motion of an object?What the four main types of friction?How do gravity and air resistance affect a falling object?In what direction does Earth’s gravity act?
12.1 Forces
Force – a push or a pull on an objectForces cause changes in velocity
Acceleration - change the objects speed or direction
Measured Scale, Force Sensor
Unit – measured in Newton’s (N) A medium apple will apply a force
of about 1 N
12.1 Force
12.1 ForcesHow do forces affect the motion of an object?
Forces are vectors so they are drawn using arrows (show magnitude and direction)
Net Force – the overall force acting on an object after all the forces are combined Balanced forces – the net force is zero,
no acceleration Unbalanced forces – objects accelerate
12.1 Force
12.1 ForcesHow do forces affect the motion of an object?
Friction – a force that opposes the motion of objects that touch as they move past each other
Four Types Static Friction – when objects aren’t
moving Sliding Friction – when objects are sliding
past each other
12.1 Force
12.1 ForcesWhat are the four main types of friction
Rolling Friction – allows movement forward, but not side to side
Fluid Friction – when an object is moving through a fluid
▪ Fluids are liquids or gases – anything that flows
▪ Air resistance is a form of fluid friction
12.1 Force
12.1 ForcesWhat are the four main types of friction
Gravity – the force of attraction between any two objects with mass Earth’s gravity points toward the center
of the earth – pulls anything with mass Called weight
12.1 Force
12.1 ForcesHow does gravity and air resistance affect a falling object
Name and describe the four types of friction.
S-26I can describe different kinds of force.
What is the difference between weight and mass.
S-27I can describe different kinds of force.
When an object is falling, two forces act on it
What do you think they are?▪ Weight▪ Air Resistance
Objects will accelerate because of gravity until they reach a terminal velocity – the speed at which the weight and air resistance are equal
For example – terminal speed of a raindrop is about
9 m/s Human – 76 m/s
12.1 Force
12.1 ForcesHow does gravity and air resistance affect a falling object
Gravity
(Weight)
Air
Resistance
How does Newton’s first law relate change in motion to a zero net force?How does Newton’s second law relate force, mass, and acceleration?How are weight and mass related?
12.2 Newton’s 1st and 2nd Laws of Motion
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow does Newton’s first law relate change in motion to a zero net force Newton’s First Law of Motion
The state of motion of an object does not change as long as the net force acting on the object is zero
More commonly▪ An object at rest remains at rest, and an
object in motion remains in motion, unless acted on by an outside force.
Sometimes called the law of inertia▪ Inertia – the tendency of an object to
resist a change in its motion
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion
The acceleration of an object is equal to the net force acting on it divided by the object’s mass.
F – Force in Newtons m – mass in kilograms a – acceleration in m/s2
Always in the same direction as the net force
F ma
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –
Practice Problems A car with a mass of 1000 kg
accelerates when the traffic light turns green. If the net force on the car is 4000 N, what is the cars acceleration?Equation?Variables?Filled In Equation?Answer?
F ma
m 1000 kgF 4000N
4000N 1000 kgb c
aa 4 m s2-
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –
Practice Problems An automobile with a mass of 1200
kg accelerates at a rate of 3.0 m/s2. What is the force acting on the automobile?Equation?Variables?Filled In Equation?Answer?
F ma
m 1200 kg
a 3.0 m s2-
F 1200 kgb c
3.0ms2ffffff
d e
F 400N
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion –
Practice Problems A 25 N force accelerates a man on a
scooter at 0.5 m/s2. What is the mass of the man and scooter?Equation?Variables?Filled In Equation?Answer?
F ma
F 25Na 0.5 m s2
-
25N m 0.5ms2ffffff
d e
m 50 kg
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow are weight and mass related Weight and Mass
Weight the force of gravity acting on an object
Its mass times acceleration due to gravity
W – Weight in Newtons m – mass in kilograms g – 9.80 m/s2
Wmg
How much force must be applied to make a 45 kg kid on a skate board accelerate at 3 m/s2?.
What is the acceleration of a 4000 kg rocket if 30,000 N of force is applied to it?
S-28I can use Newton’s 2nd Law to calculate quantities.
12.1 Force
12.2 Newton’s 1st & 2nd LawsHow are weight and mass related Weight and Mass
Mass is a measurement of the inertia of an object
Weight is a measurement of the force of gravity acting on an object
What is Newton’s third law of motion?
12.3 Newton’s 3rd Law of Motion and Momentum
12.1 Force
12.3 Newton’s 3rd LawWhat is Newton’s third law of motion
Newton’s Third Law Whenever one object exerts a force on a
second object, the second object exerts an equal and opposite force on the first object.
Identify the following action and reaction forces
12.1 Force
12.3 Newton’s 3rd LawWhat is Newton’s third law of motion
Newton’s Third Law Action-Reaction pairs can cause motion
The donkey pushes on the ground, the ground pushes the donkey forward
Does the donkey push the ground backward?
Action-Reaction pairs don’t cancel They don’t act on the same objects
Name the action reaction pairs in the following pictures.
S-29What is Newton’s Third Law of Motion.
A 45 kg duck slams into a wall going at 15 m/s. He comes to a complete stop in 3 s.
A. What is his change is velocity?B. What is his acceleration?C. What is the force on the duck?D. What is the reaction force?
S-30What is Newton’s Third Law of Motion.
What are the four fundamental forces?
12.4 Universal Forces
12.1 Force
12.4 Universal ForcesWhat are the four fundamental forces
Electromagnetic Forces Associated with charged particles Electric Force – between two charged
particles Negative and positive Opposites attract, like repels
Magnetic Force – between other magnets and certain metals
12.1 Force
12.4 Universal ForcesWhat are the four fundamental forces
Strong Nuclear Force Act to hold the nucleus together Overcomes repulsion of positive protons
with each other The strongest force over small
(tiny, tiny) distances
12.1 Force
12.4 Universal ForcesWhat are the four fundamental forces
Weak Nuclear Force Involved in certain types of radioactive
processes Active only over distances even smaller
than the strong nuclear force
12.1 Force
12.4 Universal ForcesWhat are the four fundamental forces
Gravitational Force Between any two objects with mass Depends on the mass and the distance
between the objects Very weak force Acts over
very long distances
List and briefly describe the 4 fundamental forces.
S-31What are the four fundamental forces?
A guys is smashed by another guy. A. If the guy in blue smashes the
other guy with a force of 2000 N, and the second guy has a
mass of 125kg, what is his acceleration?
B. What is the force felt by the blue guy?
S-32How does Newton’s second law relate force, mass, and acceleration?
We have a Test?
S-33
