Read: Chap 4 09/16/14 – slide 1

A100–Exploring the Universe: The Laws of Motion

Martin D. Weinberg

UMass Astronomy

weinberg@astro.umass.edu

September 16, 2014

Announcements

⊲ Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 2

MasteringAstronomy pointers (see Handouts) [example]

Announcements

⊲ Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 2

MasteringAstronomy pointers (see Handouts) [example]

Astronomy Help Desk

⊲ Mon through Thu, 7-9pm in Hasbrouck 110

Announcements

⊲ Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 2

MasteringAstronomy pointers (see Handouts) [example]

Astronomy Help Desk

⊲ Mon through Thu, 7-9pm in Hasbrouck 110

Today’s topic: Newton’s Laws of Motion and Gravity

⊲ How do we describe motion?

⊲ How is mass different from weight?

⊲ How did Newton change our view of the Universe?

⊲ What are Newton’s 3 Laws of Motion?

Announcements

⊲ Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 2

MasteringAstronomy pointers (see Handouts) [example]

Astronomy Help Desk

⊲ Mon through Thu, 7-9pm in Hasbrouck 110

Today’s topic: Newton’s Laws of Motion and Gravity

⊲ How do we describe motion?

⊲ How is mass different from weight?

⊲ How did Newton change our view of the Universe?

⊲ What are Newton’s 3 Laws of Motion?

Questions?

Scientific Progress

Read: Chap 4 09/16/14 – slide 3

“If I have seen farther than others, it is

because I have stood on the shoulders

of giants”

—Isaac Newton

Back to Galileo (review)

Announcements

Scientific Progress

⊲ Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 4

Similarity of Earth–Moon–Sun andJupiter–moons–Sun

Rolled balls down inclined planes

Found that objects increased their speed independently

of weight

Uniform, straight-line motion is the natural state for

motion of objects

Galilean relativity

⊲ The mechanical laws of physics are the same for

every inertial observer.

⊲ By observing the outcome of mechanical

experiments, one cannot distinguish a state of rest

from a state of constant velocity.

Back to Galileo (review)

Announcements

Scientific Progress

⊲ Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 4

Similarity of Earth–Moon–Sun andJupiter–moons–Sun

Rolled balls down inclined planes

Found that objects increased their speed independently

of weight

Uniform, straight-line motion is the natural state for

motion of objects

Galilean relativity

⊲ The mechanical laws of physics are the same for

every inertial observer.

⊲ By observing the outcome of mechanical

experiments, one cannot distinguish a state of rest

from a state of constant velocity.

Back to Galileo (review)

Announcements

Scientific Progress

⊲ Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 4

Similarity of Earth–Moon–Sun andJupiter–moons–Sun

Rolled balls down inclined planes

Found that objects increased their speed independently

of weight

Uniform, straight-line motion is the natural state for

motion of objects

Galilean relativity

⊲ The mechanical laws of physics are the same for

every inertial observer.

⊲ By observing the outcome of mechanical

experiments, one cannot distinguish a state of rest

from a state of constant velocity.

Back to Galileo (review)

Announcements

Scientific Progress

⊲ Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 4

Similarity of Earth–Moon–Sun andJupiter–moons–Sun

Rolled balls down inclined planes

Found that objects increased their speed independently

of weight

Uniform, straight-line motion is the natural state for

motion of objects

Galilean relativity

⊲ The mechanical laws of physics are the same for

every inertial observer.

⊲ By observing the outcome of mechanical

experiments, one cannot distinguish a state of rest

from a state of constant velocity.

Back to Galileo (review)

Announcements

Scientific Progress

⊲ Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 5

Example: centripetal motion

State of motion called inertia

Objects preserve their inertia unless acted on by a force

Acceleration by Gravity

Read: Chap 4 09/16/14 – slide 6

All falling objects accelerate at

the same rate (not counting fric-

tion of air resistance)

On Earth, g ≈ 10m/s2: speed

increases 10m/s with each sec-

ond of falling

Note: ≈ means approximately equal

Acceleration by Gravity

Announcements

Scientific Progress

Galileo

⊲Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 7

Galileo showed that g is

the same for all falling

objects, regardless of their

mass.

Acceleration by Gravity

Announcements

Scientific Progress

Galileo

⊲Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 8

Galileo’s thought experiment

Earth is sphere

Shoot a cannonball fast

enough and rate of falling

will balance curvature

[demos]

Describing motion

Read: Chap 4 09/16/14 – slide 9

Precise definitions to describe motion:

Speed: Rate at which object moves

speed =distance

time

[units of m/s, cm/s, km/s or miles/hr,

example: 10 m/s]

Velocity: Speed plus direction example:

10 m/s due East

Acceleration: Any change in velocity in

units of speed/time (m/s2) and a direc-

tion

Momentum and Force

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

⊲Momentum &Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 10

Momentum = mass × velocity

A net force changes momentum, which generally means

an acceleration (change in velocity)

Rotational momentum of a spinning or orbiting object is

known as angular momentum

Rotational force is known as torque

[demo]

Momentum and Force

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

⊲Momentum &Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 10

Momentum = mass × velocity

A net force changes momentum, which generally means

an acceleration (change in velocity)

Rotational momentum of a spinning or orbiting object is

known as angular momentum

Rotational force is known as torque

[demo]

Momentum and Force

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

⊲Momentum &Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 10

Momentum = mass × velocity

A net force changes momentum, which generally means

an acceleration (change in velocity)

Rotational momentum of a spinning or orbiting object is

known as angular momentum

Rotational force is known as torque

[demo]

Momentum and Force

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

⊲Momentum &Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 10

Momentum = mass × velocity

A net force changes momentum, which generally means

an acceleration (change in velocity)

Rotational momentum of a spinning or orbiting object is

known as angular momentum

Rotational force is known as torque

[demo]

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop.

2. A bus speeding up.

3. An elevator moving up at constant speed.

4. A bicycle going around a curve.

5. A moon orbiting Jupiter.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop. Y

2. A bus speeding up.

3. An elevator moving up at constant speed.

4. A bicycle going around a curve.

5. A moon orbiting Jupiter.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop. Y

2. A bus speeding up. Y

3. An elevator moving up at constant speed.

4. A bicycle going around a curve.

5. A moon orbiting Jupiter.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop. Y

2. A bus speeding up. Y

3. An elevator moving up at constant speed. N

4. A bicycle going around a curve.

5. A moon orbiting Jupiter.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop. Y

2. A bus speeding up. Y

3. An elevator moving up at constant speed. N

4. A bicycle going around a curve. Y

5. A moon orbiting Jupiter.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

⊲ Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 11

Is there a net force? Y/N

1. A car coming to a stop. Y

2. A bus speeding up. Y

3. An elevator moving up at constant speed. N

4. A bicycle going around a curve. Y

5. A moon orbiting Jupiter. Y

Mass and weight

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

⊲ Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 12

How is mass different from weight?

Mass—the amount of matter in an object

Weight—the force that acts upon an object

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

⊲ Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 13

On the Moon:

1. My weight is the same, my mass is less.

2. My weight is less, my mass is the same.

3. My weight is more, my mass is the same.

4. My weight is more, my mass is less.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

⊲ Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 13

On the Moon:

1. My weight is the same, my mass is less.

2. My weight is less, my mass is the same.

3. My weight is more, my mass is the same.

4. My weight is more, my mass is less.

Weightlessness

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

⊲ Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 14

Why are astronauts weightless in space?

There is gravity in

space

Weightlessness is

due to a constant

state of free-fall

Newton

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

⊲ Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 15

Newton’s significant contributions

Recognized importance of

Galileo’s contribution

Laws of Motion

Law of Gravitation

Newton

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

⊲ Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 15

Newton’s significant contributions

Recognized importance of

Galileo’s contribution

Laws of Motion

Law of Gravitation

Invented differential calculus

Newton

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

⊲ Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 16

Newton changed our view of the universe!

Realized the same physical laws

that operate on Earth also oper-

ate in the heavens

One Universe

Discovered laws of motion and

gravity

Much more: Experiments with

light; first reflecting telescope,

calculus. . .

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 17

1. Law of Inertia: A body remains at rest, or moves in a

straight line at a constant speed, unless acted on by an

outside force

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 17

1. Law of Inertia: A body remains at rest, or moves in a

straight line at a constant speed, unless acted on by an

outside force

2. Second Law: Acceleration of an object is proportional to

the force acting on that object

F = m a

m is mass

a is acceleration

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 17

1. Law of Inertia: A body remains at rest, or moves in a

straight line at a constant speed, unless acted on by an

outside force

2. Second Law: Acceleration of an object is proportional to

the force acting on that object

F = m a

m is mass

a is acceleration

3. Third Law: When one body exerts a force on a second

body, the second body exerts an equal and opposite force on

the first body

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 18

First Law: Law of Inertia

The motion of an object has speed and direction known

as momentum

An object’s resistance to changes in motion is known as

inertia

Contradicted the still popular theories of Aristotle that

objects will eventually come to rest

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 19

Second Law of Motion

F= ma

⊲ F describes the force acting

⊲ m is the mass of the object

⊲ a is its acceleration, the change in its motion.

Like motion, force has both a value or strength, and a

direction in which it acts.

Acceleration refers to any change (e.g. both “speeding

up” or “slowing down”)

Implies First Law of Motion

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 20

Second Law of Motion: examples

The larger the force ⇒ the larger the acceleration

For equal force, a larger mass must have a smaller

acceleration

Larger mass has greater inertia. Can use this to measure

mass of an object

Unit of force (metric) is called a Newton (N):

1 Newton is equal to 1 kg · m/s2

Inertial mass

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 21

Third Law: equal and opposite force

Example: smack an object

⊲ Object moves as a result

⊲ Your hand also feels a force and bounces backn

(and hurts)

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 21

Third Law: equal and opposite force

Example: smack an object

⊲ Object moves as a result

⊲ Your hand also feels a force and bounces backn

(and hurts)

Example: small object hits a large object

⊲ If the forces are equal, why does the smaller object

bounce back faster?

Newton’s 3 Laws of Motion

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

⊲ 3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 21

Third Law: equal and opposite force

Example: smack an object

⊲ Object moves as a result

⊲ Your hand also feels a force and bounces backn

(and hurts)

Example: small object hits a large object

⊲ If the forces are equal, why does the smaller object

bounce back faster?

⊲ msmallasmall = F = mlargealarge

⊲ asmall =mlarge

msmallalarge

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

⊲ Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 22

Is the force the Earth exerts on you larger, smaller, or the same

force you exert on it?

Earth exerts a larger force on you.

You exert a larger force on Earth.

You and the Earth exert equal and opposite forces on

each other.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

⊲ Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 22

Is the force the Earth exerts on you larger, smaller, or the same

force you exert on it?

Earth exerts a larger force on you.

You exert a larger force on Earth.

You and the Earth exert equal and opposite forces on

each other.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

⊲ Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 22

Is the force the Earth exerts on you larger, smaller, or the same

force you exert on it?

Earth exerts a larger force on you.

You exert a larger force on Earth.

You and the Earth exert equal and opposite forces on

each other.

⊲ msmallasmall = F = mlargealarge

⊲ alarge =msmall

mlargeasmall

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

⊲ Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 23

A compact car and a Mack truck have a head-on collision. Are

the following true or false?

1. The force of the car on the truck is equal and opposite to

the force of the truck on the car.

2. The momentum transferred from the truck to the car is

equal and opposite to the momentum transferred from

the car to the truck.

3. The change of velocity of the car is the same as the

change of velocity of the truck.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

⊲ Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 23

A compact car and a Mack truck have a head-on collision. Are

the following true or false?

1. The force of the car on the truck is equal and opposite to

the force of the truck on the car. T

2. The momentum transferred from the truck to the car is

equal and opposite to the momentum transferred from

the car to the truck.

3. The change of velocity of the car is the same as the

change of velocity of the truck.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

⊲ Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 23

A compact car and a Mack truck have a head-on collision. Are

the following true or false?

1. The force of the car on the truck is equal and opposite to

the force of the truck on the car. T

2. The momentum transferred from the truck to the car is

equal and opposite to the momentum transferred from

the car to the truck. T

3. The change of velocity of the car is the same as the

change of velocity of the truck.

Thought question

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

⊲ Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 23

A compact car and a Mack truck have a head-on collision. Are

the following true or false?

1. The force of the car on the truck is equal and opposite to

the force of the truck on the car. T

2. The momentum transferred from the truck to the car is

equal and opposite to the momentum transferred from

the car to the truck. T

3. The change of velocity of the car is the same as the

change of velocity of the truck. F

Conservation Laws

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

⊲ConservationLaws

Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 24

Why do objects move at constant velocity if no force acts

on them?

What keeps a planet rotating and orbiting the Sun?

Where do objects get their energy?

Conservation of Momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

⊲Conservation ofMomentum

Angular Momentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 25

The total momentum of

interacting objects cannot

change unless an external

force is acting on them

Interacting objects ex-

change momentum

through equal and oppo-

site forces

Angular Momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

⊲AngularMomentum

Conservation ofAngular momentum

Read: Chap 4 09/16/14 – slide 26

What keeps a planet rotating and orbiting theSun?

Conservation of Angular momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

⊲

Conservation ofAngularmomentum

Read: Chap 4 09/16/14 – slide 27

angular momentum = mass × velocity × radius

The angular momentum of an object cannot change

unless an external twisting force (torque) is acting on it

Earth experiences no twisting force as it orbits the Sun,

so its rotation and orbit will continue indefinitely

Bicycle wheel with perfect bearings will turn indefinitely

Conservation of Angular momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

⊲

Conservation ofAngularmomentum

Read: Chap 4 09/16/14 – slide 27

angular momentum = mass × velocity × radius

The angular momentum of an object cannot change

unless an external twisting force (torque) is acting on it

Earth experiences no twisting force as it orbits the Sun,

so its rotation and orbit will continue indefinitely

Bicycle wheel with perfect bearings will turn indefinitely

Conservation of Angular momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

⊲

Conservation ofAngularmomentum

Read: Chap 4 09/16/14 – slide 27

angular momentum = mass × velocity × radius

The angular momentum of an object cannot change

unless an external twisting force (torque) is acting on it

Earth experiences no twisting force as it orbits the Sun,

so its rotation and orbit will continue indefinitely

Bicycle wheel with perfect bearings will turn indefinitely

Conservation of angular momentum

Announcements

Scientific Progress

Galileo

Acceleration byGravity

Describing motion

Momentum & Force

Thought question

Mass and weight

Thought question

Weightlessness

Newton

3 Laws of Motion

Thought question

Thought question

Conservation Laws

Conservation ofMomentum

Angular Momentum

⊲

Conservation ofAngularmomentum

Read: Chap 4 09/16/14 – slide 28

Angular momentum conservation also explains why objects

rotate faster as they shrink in radius:

Tutorials

Read: Chap 4 09/16/14 – slide 29

An example from the upcoming assignment . . .

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Tutorials

Read: Chap 4 09/16/14 – slide 29

An example from the upcoming assignment . . .

[back]

Tutorials

Read: Chap 4 09/16/14 – slide 29

The tutorial appears in its own window . . .

[back]

Tutorials

Read: Chap 4 09/16/14 – slide 29

The tutorial appears in its own window . . .

[back]

Tutorials

Read: Chap 4 09/16/14 – slide 29

Scoring . . .

Tutorials

Read: Chap 4 09/16/14 – slide 29

Scoring . . .

Tutorials

Read: Chap 4 09/16/14 – slide 29

Scoring of self-guided tutorials in assignmentsThe scoring in effect for each tutorial appears on its starting page, just below

the Part label. All tutorials are scored as follows:

50% credit = Working through all parts of the tutorial

50% credit = First answer to each question in the Exercises section.

[back]

Tutorials

Read: Chap 4 09/16/14 – slide 29

Click Submit when you are completely done

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