1. Newton's First Law of Motion
Chapter 2
Newton's First Law
of Motion
- Inertia

2. Aristotle attempted to understand motion by classification.
1. ARISTOTLE ON MOTION
Aristotle attempted to understand motion by classification.
Two Classes:
Natural and Violent

3. Natural Natural motion depended on nature of the object. Examples:
A rocks falls
Smoke rises

4. The falling speed of an object was supposed to be proportional to its weight.
Natural motion could be circular (perfect objects in perfect motion with no end).

5. Violent Pushing or pulling forces imposed motion.
Some motions were difficult to understand.
Example: the flight of an arrow
There was a normal state of rest except for celestial bodies.

6. Aristotle was unquestioned for 2000 years.
Most thought that the Earth was the center of everything
for it was in its normal state.
No one could imagine a force that could move it.

7. 2. COPERNICUS AND THE MOVING EARTH
Sun was center, not earth.
He was hesitant to publish because he didn't really believe it either.
De Revolutionibus reached him on the day he died, May 24, 1543.

8. 3. GALILEO AND THE LEANING TOWER
17th Century scientist who supported Copernicus.
He refuted many of Aristotle's ideas.
Worked on falling object problem - used experiment.

9. 4. GALILEO'S INCLINED PLANES
Knocked down Aristotle's push or pull ideas.
Rest was not a natural state.
The concept of inertia was introduced.
Galileo is sometimes referred to as the
“father of experimentation.”

10. He tested with planes. Demo - Ball and incline plane
The change in speed depended on the slope of the incline.

12. 5. NEWTON’S FIRST LAW OF MOTION
Newton finished the overthrow of Aristotelian ideas.
Law 1 (Law of Inertia)
Every object continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.
“If you leave an object alone, it has constant velocity.”

13. Demonstrations Demo - Weight and string Demo - Card, cup, and coin
Demo - Swinging Rocks
Demo - Coins on elbow
Demo - Table setting
Demo - Bottle, hoop, and chalk
Demo – Lead brick and hammer

14. 6. NET FORCE
A force or a combination of forces produces changes in motion (accelerations).
10 N m = m
20 N
10 N m = m
10 N
10 N
0 N m = m
20 N
10 N
10 N

15. 7. THE EQUILIBRIUM RULE Examples of Mechanical Equilibrium:
Scales pushing up
Normal up
Computer setting on a table
Weight down
Weighing yourself on a set of scales
Hanging from a tree
Tree
pulling up
Weight down
Car parked on an incline
Normal
Friction
Weight down
Weight down

16. The Equilibrium Rule

17. 8. SUPPORT FORCE
In the first example of mechanical equilibrium the table supplied a force upward that was called the normal force. It is a support force.
Consider the second example of mechanical equilibrium. The scales supply a support force on the man.
Normal up
Weight down
Scales pushing up
Weight down

18. 9. EQUILIBRIUM OF MOVING THINGS
Equilibrium is a state of no change.
If an object moves in a straight line with no change in speed, it is in equilibrium.
Examples:
Driving at constant velocity
Normal up
Air resistance
Air
Resistance
Force from road
Weight down
Terminal velocity in parachuting
Weight down

19. 10. THE MOVING EARTH
It is hard to detect the motion of the earth because we are moving with it.
Early science could not predict large enough forces to move the earth.
Can Hewitt’s bird drop down and catch the worm if the Earth moves at 30 km/s?
Demo - Cart and ball launcher

20. Chapter 2 Review Questions

21. Which person below is most highly recognized for proposing a heliocentric universe?
(a) Aristotle
(b) Newton
(c) Galileo
(d) Copernicus
(d) Copernicus

22. If an object weighs 10 lb, what must the air resistance force be if the object is falling and has reached terminal velocity?
(a) 10 lb
(a) 10 lb
(b) 32 lb
(c) there is no way of telling without knowing what the value of the terminal velocity is

23. Newton's concept of motion said that the natural state of an object was
(a) constant velocity
(a) constant velocity
(b) constant acceleration
(c) constant net force

24. Chapter 2 Demonstrations
Ball and incline plane
Weight and string
Card, cup, and coin
Swinging Rocks
Coins on elbow
Table setting
Bottle, hoop, and chalk
Cart and ball launcher