Newton’s Laws February 20, 2013 - p. 1/9

February 20, Week 6

Today: Chapter 4, Newton’s Laws

Exam #1 is in mailboxes

Homework Assignment #5 - Due March 1.

Mastering Physics: 10 problems from chapters 4 and 5.

Written Questions: 5.74

Jonathan not here Thursday.

Newton’s Laws February 20, 2013 - p. 2/9

Review

First Law - The Law of Inertia

An object at rest stays at rest, an object in uniform motionstays if uniform motion if (and only if) the net force acting onthe object is zero.

Newton’s Laws February 20, 2013 - p. 2/9

Review

First Law - The Law of Inertia

An object at rest stays at rest, an object in uniform motionstays if uniform motion if (and only if) the net force acting onthe object is zero.

Second Law

Σ−→

F = M−→a

Newton’s Laws February 20, 2013 - p. 2/9

Review

First Law - The Law of Inertia

An object at rest stays at rest, an object in uniform motionstays if uniform motion if (and only if) the net force acting onthe object is zero.

Second Law

Σ−→

F = M−→a

Units: N = kg ·m/s2

Newton’s Laws February 20, 2013 - p. 2/9

Review

First Law - The Law of Inertia

An object at rest stays at rest, an object in uniform motionstays if uniform motion if (and only if) the net force acting onthe object is zero.

Second Law

Σ−→

F = M−→a

Units: N = kg ·m/s2

w = Mg

Newton’s Laws February 20, 2013 - p. 3/9

Second Law Examples

Example: A 6860N car is traveling with a speed of 30m/s

when the driver removes her foot from the gas pedal, makingthe engine force zero. If the frictional force is 350N , what is thecar’s acceleration?

Newton’s Laws February 20, 2013 - p. 3/9

Second Law Examples

Example: A 6860N car is traveling with a speed of 30m/s

when the driver removes her foot from the gas pedal, makingthe engine force zero. If the frictional force is 350N , what is thecar’s acceleration?

An object already in motion will not move in the direction of thenet force. It will accelerate in the direction of the net force.

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

C

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

C

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

C

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

C

D

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

C

D(e)

Not enoughinformationto determine

Newton’s Laws February 20, 2013 - p. 4/9

Second Law Exercise

A spaceship is floating sideways from point A to B in themiddle of outer space. At B the spaceship turns on it’s enginesfor 5 s and moves to point C. At C the engines are again turnedoff and the spaceship floats to point D. Which of the followingpicture correctly shows the spaceship’s trajectory from A to D?

(a)A B

CD

(b)A B

CD

(c)A B

C

D

(d)A B

C

D(e)

Not enoughinformationto determine

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

From A to B rocket goes onstraight line since no force ⇒

uniform motion

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

From A to B rocket goes onstraight line since no force ⇒

uniform motion

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

From A to B rocket goes onstraight line since no force ⇒

uniform motion

When rockets turned on thiscauses an acceleration in y-direction but NOT x-direction ⇒

acceleration motion in y, uniformmotion in y ⇒ curved motion

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

C

From A to B rocket goes onstraight line since no force ⇒

uniform motion

When rockets turned on thiscauses an acceleration in y-direction but NOT x-direction ⇒

acceleration motion in y, uniformmotion in y ⇒ curved motion

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

C

From A to B rocket goes onstraight line since no force ⇒

uniform motion

When rockets turned on thiscauses an acceleration in y-direction but NOT x-direction ⇒

acceleration motion in y, uniformmotion in y ⇒ curved motion

When rockets turned off againwe go back to uniform motion⇒ straight line. But now wehave velocity in both x- and y-directions ⇒ straight line at anangle

Newton’s Laws February 20, 2013 - p. 5/9

Exercise Followup

A B

C

D

From A to B rocket goes onstraight line since no force ⇒

uniform motion

When rockets turned on thiscauses an acceleration in y-direction but NOT x-direction ⇒

acceleration motion in y, uniformmotion in y ⇒ curved motion

When rockets turned off againwe go back to uniform motion⇒ straight line. But now wehave velocity in both x- and y-directions ⇒ straight line at anangle

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

A B

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

A B

−→

FA on B−→

FA on B = Force that A exerts on B

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

A B

−→

FA on B

−→

FB on A

−→

FA on B = Force that A exerts on B

−→

FB on A = Force that B exerts on A

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

A B

−→

FA on B

−→

FB on A

−→

FA on B = Force that A exerts on B

−→

FB on A = Force that B exerts on A

Third Law :−→

FB on A = −

−→

FA on B

Newton’s Laws February 20, 2013 - p. 6/9

Newton’s Third Law

For every action, there is an equal but opposite reaction.

A B

−→

FA on B

−→

FB on A

−→

FA on B = Force that A exerts on B

−→

FB on A = Force that B exerts on A

Third Law :−→

FB on A = −

−→

FA on B

Action and Reaction are applied to different objects!

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

(b) The soccer ball exerts a larger force on Messi than he exertson it.

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

(b) The soccer ball exerts a larger force on Messi than he exertson it.

(c) Messi exerts an equal force to the one the soccer ball exertson him.

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

(b) The soccer ball exerts a larger force on Messi than he exertson it.

(c) Messi exerts an equal force to the one the soccer ball exertson him.

(d) Sometimes the force exerted by Messi is larger than what thefootball exerts on him. It depends on how hard he kicks it.

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

(b) The soccer ball exerts a larger force on Messi than he exertson it.

(c) Messi exerts an equal force to the one the soccer ball exertson him.

(d) Sometimes the force exerted by Messi is larger than what thefootball exerts on him. It depends on how hard he kicks it.

(e) None of the above

Newton’s Laws February 20, 2013 - p. 7/9

Third Law Exercise

Whenever Lionel Messi kicks a soccer ball, which of thefollowing is a true statement?

(a) Messi exerts a larger force on the soccer ball than it exerts onhim.

(b) The soccer ball exerts a larger force on Messi than he exertson it.

(c) Messi exerts an equal force to the one the soccer ball exertson him.

(d) Sometimes the force exerted by Messi is larger than what thefootball exerts on him. It depends on how hard he kicks it.

(e) None of the above

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

−→

KM on B

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

−→

KM on B

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

−→

KM on B

−→

fB

−→nB

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

−→

KB on M

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Forces on Messi from ground: Nor-

mal −→nM , static friction−→

fM−→

KB on M

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Forces on Messi from ground: Nor-

mal −→nM , static friction−→

fM−→

KB on M −→

fM

−→nM

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Forces on Messi from ground: Nor-

mal −→nM , static friction−→

fM

Long-Range Force on Messi: Weight −→wM

−→

KB on M −→

fM

−→nM

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Forces on Messi from ground: Nor-

mal −→nM , static friction−→

fM

Long-Range Force on Messi: Weight −→wM

−→

KB on M −→

fM

−→nM

−→wM

Newton’s Laws February 20, 2013 - p. 8/9

Third Law Followup

Forces on Ball from Messi: Kick−→

KM on B

Forces on Ball from ground: Normal−→nB , static friction

−→

fB

Long-Range Force on Ball: Weight −→wB

−→

KM on B

−→

fB

−→nB

−→wB

Forces on Messi from Ball: Kick−→

KB on M

Forces on Messi from ground: Nor-

mal −→nM , static friction−→

fM

Long-Range Force on Messi: Weight −→wM

−→

KB on M −→

fM

−→nM

−→wM

End Result: Ball moves, Messi does not

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

(c) The 200N downwards force on the earth

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

(c) The 200N downwards force on the earth

(d) The 200N upwards force on the earth

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

(c) The 200N downwards force on the earth

(d) The 200N upwards force on the earth

(e) Intentionally left blank

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

(c) The 200N downwards force on the earth

(d) The 200N upwards force on the earth

(e) Intentionally left blank Weight =−→w =

−→

FE on B =

downwards force that earthexerts on box

Newton’s Laws February 20, 2013 - p. 9/9

Third Law Exercise

A 200-N crate is placed on a horizontal surface. The reactionto the force of gravity on the crate is:

(a) The 200N upwards normal force on the crate

(b) The 200N downwards force on the crate

(c) The 200N downwards force on the earth

(d) The 200N upwards force on the earth

(e) Intentionally left blank Weight =−→w =

−→

FE on B =

downwards force that earthexerts on box

Reaction =−→

FB on E upwardsforce that box exerts on earth