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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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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
1st 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

3.2 Newton’s First Law of Motion

3 3 newton s second law of motion1
2nd 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

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

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
  • 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 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 motion3
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.
  • What is the acceleration of
  • the man?
  • B. What is the acceleration of the canoe?

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
Nb

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
Nb

Nf

T2

T1

T2

Wf

Equations

Solve (add)

3.4 Newton’s Third Law of Motion

Wb

3 5 the vector nature of forces2
L

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 forces1
Friction – force that opposes motion

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

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
  • Static – object at rest
  • Kinetic – object in motion
  • 3.Rolling – just like it sounds

3.6 Frictional Forces

3 6 frictional forces4
Example

3.6 Frictional Forces

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