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Newtons First Law of Motion - PowerPoint PPT Presentation

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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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Chapter 2

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 motion depended on nature of the object.


A rocks falls

Smoke rises

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).

Violent proportional to its weight.

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.

Aristotle was unquestioned for 2000 years
Aristotle was unquestioned for 2000 years. proportional to its weight.

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.

2 copernicus and the moving earth
2. COPERNICUS proportional to its weight. ANDTHE 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.

3 galileo and the leaning tower
3. GALILEO proportional to its weight. AND THE LEANING TOWER

17th Century scientist who supported Copernicus.

He refuted many of Aristotle's ideas.

Worked on falling object problem - used experiment.

4 galileo s inclined planes
4. GALILEO'S INCLINED PLANES proportional to its weight.

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.”

He tested with planes
He tested with planes. proportional to its weight.

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.”

Demonstrations proportional to its weight.

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.







A force or a combination of forces produces changes in motion (accelerations).

10 N


20 N

10 N


10 N

10 N

0 N


20 N

10 N

10 N

7. THE EQUILIBRIUM RULE proportional to its weight.

Scales pushing up

Examples of



Normal up

Computer setting on a table

Weight down

Weighing yourself on a set of scales

Hanging from a tree


pulling up

Weight down

Car parked on an incline



Weight down

Weight down

The Equilibrium Rule proportional to its weight.

Scales pushing up proportional to its weight.

Normal up

Weight down

Weight down


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

Normal up

Air resistance



Force from road

Weight down

Terminal velocity in parachuting

Weight down

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

Chapter 2 review questions

Chapter 2 Review Questions proportional to its weight.

Which person below is most highly recognized for proposing a heliocentric universe
Which person below is most highly recognized for proposing a heliocentric universe?

(a) Aristotle

(b) Newton

(c) Galileo

(d) Copernicus

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

Newton s concept of motion said that the natural state of an object was
Newton's concept of motion said that the natural state of an object was

(a) constant velocity

(b) constant acceleration

(c) constant net force