Chapter 2. Newton's First Law of Motion. - Inertia. 1. ARISTOTLE ON MOTION. Aristotle attempted to understand motion by classification . Two Classes: Natural and Violent. Natural. Natural motion depended on nature of the object. Examples: A rocks falls . Smoke rises.
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Newton's First Law
Aristotle attempted to understand motion by classification.
Natural and Violent
Natural motion depended on nature of the object.
A rocks falls
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).
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.
Most thought that the Earth was the center of everything
for it was in its normal state.
Little did they know that it was
No one could imagine a force that could move it.
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.
17th Century scientist who supported Copernicus.
He refuted many of Aristotle's ideas.
Worked on falling object problem - used experiment.
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.”
Demo - Ball and Incline Plane
The change in speed depended on the slope of the incline.
5. NEWTON’S FIRST LAW OF MOTION proportional to its weight.
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.”
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
m proportional to its weight.
6. NET FORCE
A force or a combination of forces produces changes in motion (accelerations).
7. THE EQUILIBRIUM RULE proportional to its weight.
Scales pushing up
Computer setting on a table
Weighing yourself on a set of scales
Hanging from a tree
Car parked on an incline
The Equilibrium Rule proportional to its weight.
Scales pushing up proportional to its weight.
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.
9. EQUILIBRIUM OF MOVING THINGS proportional to its weight.
Equilibrium is a state of no change.
If an object moves in a straight line with no change in speed, it is in equilibrium.
Driving at constant velocity
Force from road
Terminal velocity in parachuting
10. THE MOVING EARTH proportional to its weight.
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
Video– Snowmobile and Flare
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
(b) 32 lb
(c) there is no way of telling without knowing what the value of the terminal velocity is
(a) constant velocity
(b) constant acceleration
(c) constant net force