1. Newton’s Laws of Motion

2. Aristotle on Motion Aristotle divided motion into 2 kinds
Natural motion-straight up or straight down
i.e. the falling of a boulder toward the ground
i.e. the rising of smoke through the air
For the heavens, circular motion was natural-therefore, the planets and stars moved in perfect circles around the earth.
Violent motion-imposed motion
i.e. a cart moves because a horse pulls it.
Has an external cause (external Force)
Force=a push or a pull

3. Copernicus and the Moving Earth
Reasoned from Astronomical observations that the earth traveled around the sun.
Extremely controversial idea.

4. Galileo on Motion First to show Copernicus’ ideas were reasonable
Determined that only when friction is present is a force necessary to keep an object moving
Friction: the force that acts between
materials as they are moving past each other
Force: a push or a pull
Used inclined planes to prove his idea
Conclusion: Every object has inertia
Inertia: object’s resistance to a change in
motion

5. Eureka !!!

6. Newton’s 1st Law of Motion
Usually called the Law of Inertia
Every object continues in its state of rest or of motion in a straight line at a constant speed unless it is compelled to change that state by forces exerted on it. Or
Objects tend to keep on doing what they’re already doing

7. Mass-A Measure of Inertia
Mass-the measure of the amount of inertia an object has; the measure of the amount of matter in an object-measured in kilograms (kg)
Examples- (Do not write) Suppose you kick an empty Coke can. Now kick the same can filled with soda. Now kick the same can filled with lead (very dense material)
You would barely feel the empty can, feel a little resistance with the soda, and hurt your foot with the lead. The heavier object resists you changing its motion the most; therefore it has the most inertia

8. Mass
Mass is not volume
Volume-the amount of space an object occupies-measured in cubic centimeters (cc or cm)
Styrofoam is an example of a material that may have a large volume but small mass. (low density)

9. Mass is not Weight
Mass is a measure of the number and kind of atoms that make up an object
Weight is a measure of the gravitational attraction an object has to the earth.

10. (Review) Friction: the force that acts between
materials as they are moving past each other
Force: a push or a pull

11. Unit of Force
The unit of force is the Newton, named after Sir Isaac Newton. 1 Newton of force is the effort needed to accelerate a 1 kg object at 1 m/s/s.
1 Newton of force is approximately the force needed to hold a quarter pound cheeseburger off the ground.

12. Summary
Galileo concluded that if it were not for fricton, an object would keep moving forever.
According to Newton’s first law of motion every object continues in its state of rest or motion in a straight line at constant speed unless forces cause it to change its state.
Inertia is the resistance an object has to a change in its state of motion.

13. Eureka !!!

14. Force Causes Acceleration
Net Force-The combination of all forces that act on an object
The acceleration of an object is directly related to the net force on an object (force and acceleration change in the same direction)

15. Mass Resists Acceleration
Acceleration is inversely proportional to mass
Inversely-the 2 values change in opposite directions
As mass increases, acceleration decreases for a given force
As mass decreases, acceleration increases for a given force

16. A=F/M Newton’s Second Law Also called the Law of Acceleration
The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction of the net force, and is inversely proportional to the mass of the body. or
A=F/M

17. What is Weight? Weight-The force of gravity acting on an object
Since F=MA and weight is a force
F=Mg where g=10 m/s/s on earth (different on different planets

18. Interactions Produce Forces
Forces occur in pairs-they are part of an interaction-a mutual action
For example-Consider a hammer striking a nail.
The hammer imparts a force on the nail, driving it into the wood.
The nail imparts a force on the hammer, stopping the motion of the hammer.
The forces are equal

19. Newton’s Third Law of Motion
Whenever an object exerts a force on a second object, the second object exerts a force of equal magnitude in the opposite direction on the first object.
First Object
(Hammer)
Second Object
(Nail)
Physics 1 (Garcia) SJSU
10-Nov-18

20. For every action, there is an equal and opposite reaction
Newton’s Third Law or
For every action, there is an equal and opposite reaction

21. Identifying Action and Reaction
Simple recipe for treating forces
Object A exerts a force on object B
Object B exerts a force on object A
Car exerts a force on tree
Tree exerts an equal but opposite force on the car

22. Check Yourself
A 2 ton car, going 60 m.p.h. hits a 5 ton truck, going 20 m.p.h..
The force of impact is greatest on which vehicle, the car or the truck?
The change in velocity (the acceleration) is greatest for which vehicle?
By what principle of physics?
Physics 1 (Garcia) SJSU
10-Nov-18

23. Check Yourself
Arnold Strongman and Suzie Small pull on opposite ends of a rope in a tug of war. The greater force exerted on the rope is by
1. Arnold.
2. Suzie.
3. Neither. The force is the same.
Ch 5-5
Physics 1 (Garcia) SJSU
10-Nov-18

24. Action-Reaction Pairs
Here are some examples of action-reaction pairs.
Think of examples of an object exerting a force on a second object.
Practice identifying action-reaction pairs.
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Physics 1 (Garcia) SJSU
10-Nov-18

25. More Action/Reaction Action-The earth is pulling down on the skydivers
Reaction-The skydivers are pulling up on the earth
So why doesn’t the earth move?

26. Action/Reaction on different masses
The earth DOES fall up toward the skydivers. However, the earth is MUCH MUCH larger than the skydivers so the acceleration is MUCH MUCH less
From Newton’s second law, the acceleration is equal to the force divided by the mass or
A=F/M

27. Skydiver’s Acceleration
Force/small mass=large acceleration
Earth’s Acceleration
Force/Large mass=small acceleration
Even though the same force acts on both objects, the acceleration of the earth is much smaller because its mass is so much bigger

28. Newton’s Laws Test Time!!!
Yeah!!!!