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N e w t o n’ s L a w s. Unit 3. 3.1 Force and Mass. Force – push or pull; required to change an object’s motion. Vector – so magnitude and direction Example of Contact Forces Friction Tension Applied Spring. Examples of Field Forces Gravitational Electric Magnetic.

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N e w t o n s l a w s

Newton’sLaws

Unit 3



3 1 force and mass1

Force – push or pull; required to change an object’s motion.

Vector – so magnitude and direction

Example of Contact Forces

Friction

Tension

Applied

Spring

Examples of Field Forces

Gravitational

Electric

Magnetic

3.1 Force and mass


3 1 force and mass2

Mass – measurement of how difficult it is to change the objects velocity

Inertia – resistance to change in velocity

So mass is a measurement of an object’s inertia

3.1 Force and mass



3 2 newton s first law of motion1

1 objects velocityst Law

An object at rest remains at rest as long as no net force acts on it.

An object moving with constant velocity continues to move with the same speed and in the same direction as long as no net force acts on it.

3.2 Newton’s First Law of Motion


3 2 newton s first law of motion2

Sometimes called the Law of Inertia objects velocity

3.2 Newton’s First Law of Motion



3 3 newton s second law of motion1

2 objects velocitynd Law

A net force causes an acceleration in the direction of the net force.

Simulation

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion2

N objects velocity

W

Free body diagrams

Show all the forces acting on an object

For example an object sitting on a table

W – weight = mg

N – Normal Force (perpendicular) to the surface

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion3

N objects velocity

T

W

Free body diagrams

If a rope pulls the object toward the right, then

T = Tension

Practice Free Body

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion4

  • Free body diagrams objects velocity

  • Steps in problems solving

  • Sketch the forces

  • Isolate the Object

  • Choose a Coordinate System

  • Resolve the Forces into Components

  • Apply Newton’s Second Law of Motion

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion5

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion6

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

Free Body

diagram

3.3 Newton’s Second Law of Motion


3 3 newton s second law of motion7

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

Free Body

diagram

N

T

3.3 Newton’s Second Law of Motion

W


3 3 newton s second law of motion8

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

Free Body

diagram

Axis

N

T

3.3 Newton’s Second Law of Motion

W


3 3 newton s second law of motion9

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

Free Body

diagram

Axis

Ty

N

T

3.3 Newton’s Second Law of Motion

Tx

W


3 3 newton s second law of motion10

A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?

Free Body

diagram

Axis

Equation

Ty

N

3.3 Newton’s Second Law of Motion

Tx

W


3 4 newton s third law of motion

3.4 Newton’s Third Law of Motion with a force of 80 N at an angle of 30


3 4 newton s third law of motion1

For every force that acts on an object, there is a reaction force acting on a different object that is equal in magnitude and opposite in direction.

If object 1 exerts a force F on object 2, then object 2 exerts a force –F on object 1.

3.4 Newton’s Third Law of Motion


3 4 newton s third law of motion2

What are the action reaction pairs in the following? force acting on a different object that is equal in magnitude and opposite in direction.

3.4 Newton’s Third Law of Motion


3 4 newton s third law of motion3

3.4 Newton’s Third Law of Motion


3 4 newton s third law of motion4

A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.

Free Body Diagrams

Nc

Nm

3.4 Newton’s Third Law of Motion

P

P

Wm

Wc


3 4 newton s third law of motion5

A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.

Equations

Nc

Nm

3.4 Newton’s Third Law of Motion

P

P

Wm

Wc


3 4 newton s third law of motion6

A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.

A-acceleration of man

Nc

Nm

3.4 Newton’s Third Law of Motion

P

P

Wm

Wc


3 4 newton s third law of motion7

A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.

A – acceleration of canoe

Nc

Nm

3.4 Newton’s Third Law of Motion

P

P

Wm

Wc


3 4 newton s third law of motion8

Two boxes are tied together with a rope, and the first one is pulled by a second rope. Both boxes accelerate at 2.0 m/s2. If the front box has a mass of 25 kg, and the second a mass of 50 kg, what is the tension on each rope?

a

3.4 Newton’s Third Law of Motion


3 4 newton s third law of motion9

N is pulled by a second rope. Both boxes accelerate at 2.0 m/sb

Nf

T2

T1

T2

Wf

Free body diagrams

3.4 Newton’s Third Law of Motion

Wb


3 4 newton s third law of motion10

N is pulled by a second rope. Both boxes accelerate at 2.0 m/sb

Nf

T2

T1

T2

Wf

Equations

Solve (add)

3.4 Newton’s Third Law of Motion

Wb


3 5 the vector nature of forces

3.5 The Vector Nature of Forces is pulled by a second rope. Both boxes accelerate at 2.0 m/s


3 5 the vector nature of forces1

Forces are vectors, so they can be treated using vectors rules

3.5 The Vector Nature of Forces


3 5 the vector nature of forces2

L rules

B

W

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Free Body Diagram?

3.5 The Vector Nature of Forces


3 5 the vector nature of forces3

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Components?

L

B

By

3.5 The Vector Nature of Forces

Bx

W


3 5 the vector nature of forces4

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Components?

Ly

L

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 5 the vector nature of forces5

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Equations?

Ly

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 5 the vector nature of forces6

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Values?

Ly

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 5 the vector nature of forces7

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Values?

Ly

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 5 the vector nature of forces8

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Solve?

Ly

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 5 the vector nature of forces9

Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?

Solve?

Ly

By

3.5 The Vector Nature of Forces

Bx

Lx

W


3 6 frictional forces

3.6 Frictional Forces (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28


3 6 frictional forces1

Friction – force that opposes motion (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28

Caused by microscopic irregularities of a surface

Increases as pushing

force increases

3.6 Frictional Forces


3 6 frictional forces2

Depends on the normal force and the type of surface (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28

f – force of friction (N)

N – normal force

m – coefficient of friction (1 or less)

3.6 Frictional Forces


3 6 frictional forces3

  • Three types of friction (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28

  • Static – object at rest

  • Kinetic – object in motion

  • 3.Rolling – just like it sounds

3.6 Frictional Forces


3 6 frictional forces4

Example (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28

3.6 Frictional Forces


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