Chapter 2 Chapter 2 Newton's First Law of Motion - Inertia
Jan 14, 2016
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