Chapter 2Chapter 2

Newton's First Law

of Motion - Inertia

1. ARISTOTLE ON MOTION1. ARISTOTLE ON MOTION

•Aristotle attempted to understand motion by classification

•Two Classes:

– Natural and Violent

•Aristotle attempted to understand motion by classification

•Two Classes:

– Natural and Violent

Natural MotionNatural Motion• Natural motion depended on nature of the

object.• Examples:• A rocks falls because it is heavy, a cloud floats

because it’s light• The falling speed of an object was supposed to

be proportional to its weight.

• Natural motion depended on nature of the object.

• Examples:• A rocks falls because it is heavy, a cloud floats

because it’s light• The falling speed of an object was supposed to

be proportional to its weight.

Natural MotionNatural Motion

• Natural motion could be circular (perfect objects in perfect motion with no end).

• Natural motion could be circular (perfect objects in perfect motion with no end).

Violent MotionViolent Motion

• 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.

• 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• 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.

• 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.

2. COPERNICUS ANDTHE MOVING EARTH

2. COPERNICUS ANDTHE MOVING EARTH

• Sun was center, not earth. (Heliocentric)

• 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.

• Sun was center, not earth. (Heliocentric)

• 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.

• 17th Century scientist who supported Copernicus.

• He refuted many of Aristotle's ideas.

• Worked on falling object problem - used experiment.

3. GALILEO AND THE LEANING TOWER

3. GALILEO AND THE LEANING TOWER

4. GALILEO'S INCLINED PLANES4. 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.”

• 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.”

GalileoGalileo

• He tested with planes.

• Demo - Ball and Incline PlaneDemo - Ball and Incline Plane

• The change in speed depended

on the slope of the incline.

• He tested with planes.

• Demo - Ball and Incline PlaneDemo - Ball and Incline Plane

• The change in speed depended

on the slope of the incline.

5. NEWTON’S FIRST LAW OF MOTION

5. NEWTON’S FIRST LAW OF MOTION

• Newton finished the overthrow of Aristotelian ideas.

• Law 1 (Law of Inertia)

• An object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an outside force.

• Newton finished the overthrow of Aristotelian ideas.

• Law 1 (Law of Inertia)

• An object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an outside force.

DemonstrationsDemonstrations

Demo - Weight and StringDemo - Weight and String

Demo - Card, Cup, and CoinDemo - Card, Cup, and Coin

Demo - Swinging RocksDemo - Swinging Rocks

Demo - Coins on ElbowDemo - Coins on Elbow

Demo - Table SettingDemo - Table Setting

Demo - Bottle, Hoop, and ChalkDemo - Bottle, Hoop, and Chalk

Demo – Lead Brick and Hammer Demo – Lead Brick and Hammer

Demo - Weight and StringDemo - Weight and String

Demo - Card, Cup, and CoinDemo - Card, Cup, and Coin

Demo - Swinging RocksDemo - Swinging Rocks

Demo - Coins on ElbowDemo - Coins on Elbow

Demo - Table SettingDemo - Table Setting

Demo - Bottle, Hoop, and ChalkDemo - Bottle, Hoop, and Chalk

Demo – Lead Brick and Hammer Demo – Lead Brick and Hammer

10 N

6. NET FORCE6. NET FORCE

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

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

10 N m10 N

= 20 N m

10 Nm10 N = 0 N m

10 Nm20 N = m

Examples of MechanicalEquilibrium:

Normal up

Weight down

Weight down

Weight downWeight down

Scales pushing up

Tree pulling up

NormalFriction

7. THE EQUILIBRIUM RULE7. THE EQUILIBRIUM RULE

• Computer setting on a table• Weighing yourself on a set of scales

• Hanging from a tree• Car parked on an incline

• Computer setting on a table• Weighing yourself on a set of scales

• Hanging from a tree• Car parked on an incline

The Equilibrium RuleThe Equilibrium Rule

0F

Scales pushing up

Weight down

8. SUPPORT FORCE8. 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.

• 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

9. EQUILIBRIUM OF MOVING THINGS9. 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.

• 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

Force from road

AirResistance

Normal up

Weight down

Terminal velocity in parachuting

Weight down

Air resistance

10. THE MOVING EARTH10. 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• Video – Snowmobile and Flare

• 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