1. Inertia!

2. History ~300 B.C.E. Aristotle (Greek)
Divided motion into two categories:
Natural motion: straight up or straight down
Violent motion: result of force
Any movement “against nature” was because of a force
Everything rests on Earth; Earth is too big to move

3. Copernicus ~1500 C.E. Studied astronomy
Observed that astronomy worked better if Sun was center of solar system
Theorized that the Earth did move

4. Galileo
~1600 C.E.
Argued that objects only stop moving because of friction
Friction: force that opposes movement
Occurs between two touching objects
:., objects in motion should stay in motion without friction

5. Inertia Galileo called this idea inertia
Inertia allows objects to resist changes in motion

6. Newton ~1700 C.E. Re-stated Galileo’s ideas in his 1st law of motion
Objects continue at rest or in a straight line at a uniform speed, unless acted on by a nonzero net force
Newton’s First Law of motion (aka law of inertia)

7. Vocabulary
Friction
Inertia
Law of inertia
Mass
Weight
newton

8. Objects at rest
An object at rest will stay there unless an outside force acts upon it
That force upsets the equilibrium and will start the object moving

9. Objects in motion Once in motion, the net force becomes zero again
Only another force will make it slow down or change direction

10. What does the amount of inertia depend on?
Mass

11. Mass is not….. Volume (a large size does not equal a large mass)
Weight (weight depends on gravity, which is different in different places)

12. Mass is Inertia Mass is the amount of matter in an object
The more mass, the more inertia an object has
Mass is measured in kilograms (kg)
Weight is the force of gravity
Weight is measured in newtons (N)

13. Relative Motion Does a rock move sideways as it falls?
Why doesn’t it, if the Earth is moving?

14. Relative Motion Objects move with the earth
The rock is moving with the earth as it falls, so it does not seem to move sideways

15. Relative Motion

16. Relative Motion High speed vehicles demonstrate this concept.
Dropping a rock in a plane has the same effect.
The rock moves with the plane