1. Newton’s First Law of Motion - Inertia
Chapter 4
Newton’s First Law of Motion - Inertia

2. Things want to be at rest Natural Motions:
Aristotle
Things want to be at rest
Natural Motions:
heavy things go down
light things go up
stars make circles
planets are ‘wanderers’

3. Photographic evidence of stars moving in circles

4. Aristotle II Violent Motions: Motion caused by something
Sail pushes boat
Bow shoots arrow

5. Galileo Force: a push or pull
Friction: force that acts between materials that touch caused by surface irregularities

6. Galileo
Only when friction is present is force needed to keep an object moving

7. Objects want to be at a constant velocity:
Newton
Objects want to be at a constant velocity:
“Objects at rest tend to stay at rest” - velocity of zero

8. Do you believe Newton?
“Objects at rest tend to stay at rest”
Tests?

9. Newton “Objects in motion, tend to stay in motion”
Objects will move in the same direction and same velocity with out gravity, friction, or air resistance

10. Newton’s First law of Motion (Law of Inertia)
Objects tend to stay at a constant velocity.

11. Mass
A measurement of the amount of matter (stuff) in an object
Units: Grams/kilogram

12. Amount of force that gravity places on an object
Weight
Amount of force that gravity places on an object
Units: Newton
1 kg = 9.8 N

13. Calculating Weight
Weight = gravity * mass
9.8(m/s2)*1(kg) = 9.8(N)

14. Comparing
Mass vs. Weight vs. Volume
Same mass -> same place -> same weight
Same volume -> same material -> same mass

15. Subtract opposite forces Add forces in same direction
Net Forces: Vectors!
Subtract opposite forces
Add forces in same direction
Force remaining is net force

16. Equilibrium
Forces all cancel -
0 net force

17. The air is moving with the earth!
The earth is moving!
Bird and worm
Jumping in the air
Coin in a car/plane
The air is moving with the earth!