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1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no...

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1 AP Physics Exam 2 Review Chapter 5-8
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Page 1: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

1

AP Physics Exam 2 Review

Chapter 5-8

Page 2: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

2

Newton’s Three Laws of Motion

1st: An object with no net force acting on it remains at rest or moves with constant velocity in a straight line.

2nd:

3rd: When one object exerts a force on a second object, the second object also exerts a force on the first object that is equal in magnitude but opposite in direction.

F ma

Action and reaction forces always exist together.

Page 3: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

3

Free Body (Force) Diagram

Draw all forces acting on the object being considered– Ignore all forces this object acting on other objects– Draw forces starting from center of object or at

points of action– Make sure each force giver can be identified

Page 4: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

4

Normal Force (N, but not Newton)

Given by the surface in contact to support the object.

NN

N

Fapp

• No contact No normal force• No tendency to move into surface No normal force

Always perpendicular to the surface in contact. Points from surface to the object

Page 5: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

5

Tension

Tension is along the string and points away from the object of consideration.

T

Page 6: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

6

Weight and Apparent Weight

Apparent weight is either tension or normal force.

T

W mgN

Weight or gravity: gravitational force the Earth pulling on object around it

Always straight downward.

Page 7: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

7

Two kinds of frictions

Static friction: ,maxs sf N

k kf N Kinetic (or sliding) friction:

s sf N

Page 8: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

8

Examples of centripetal forces

Rounding a curve in a car

max sv Rg

tanv Rg

Max velocity w/o skidding

– Flat curve:

– Banked curve:

Orbiting the Earth (Sun or other object)– Gravity

N

f

W

Static friction provides the centripetal force (when no skidding)

a component of Normal force (net force)

Rear View

N

W

No friction2

1tanv

Rg

Page 9: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

9

Kinetic Energy, K

Kinetic Energy: ability to do work due to motion

21

2K mv

Page 10: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

10

Work Done by A Constant Force

W F d ����������������������������

W: a scalar, no direction W < 0 if > 90o.

cosFd x x y y z zF d F d F d

F

d

Page 11: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

11

Work-Kinetic Energy Theorem

The total work done on an object is equal to the change in the kinetic energy of that object

W K f iK K

Page 12: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

12

Work (Wg) Done by Weight (Fg)

cosgW mgd

gW mg h

cosW Fd

Page 13: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

13

Work Done by a Variable Force

W Fd 1-D

or: Area under curve of

Force-position graph

( )f

i

x

x

W F x dx

Page 14: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

14

Spring Force and Work

Hook’s Law: Spring force is given by

Notice that this force is the force exerted by the spring, not the force you apply to compress or stretch the spring.

o r F F kk x x ����������������������������

sW 2 21 1

2 2s i fW kx kx f

i

x

xFdx f

i

x

xkx dx

Work done by spring force:

Page 15: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

15

Power

Average Power: WP

t

dWP

dt F v

cosFv or x x y y z zF v F v F v

Instantaneous Power:

Page 16: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

16

Potential Energy U (Ug or Usp)

Gravitational Potential Energy:

gU mgy

21

2spU kx

Spring (Elastic) Potential Energy:

Page 17: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

17

Force and Potential Energy

dUF

dx

For each potential energy, there is a conservative force associated with it.

U W

Page 18: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

18

(Total) Mechanical Energy, E

Sum of kinetic and potential energy:

mecE K U

E K U

or simply,

g sK U U

Page 19: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

19

Conservation of Mechanical Energy

When only conservative forces are doing work within a system, the kinetic energy and potential energy can change. However, their sum, the mechanical energy E of the system, remains unchanged.

i fE E

i i f fK U K U 0E K U

K U

Page 20: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

20

Work Done By External Force

Work done by external force will change the total mechanical energy of the system:

ext mecW E

If there is also kinetic friction,

ext f mecW W E ext mec thW E E

where is the heat gain (change in thermal energy) f kthE W f d

Total Energy: inttot mec thE E E E

Eint = Chemical Energy & Nuclear Energy

Page 21: 1 AP Physics Exam 2 Review Chapter 5-8. 2 Newton’s Three Laws of Motion 1 st :An object with no net force acting on it remains at rest or moves with constant.

21

Work and Energy Change

ext mecW E

Total work done by __________________________.

W K

Total work done by _______________________________.

Work-Kinetic Energy Theorem:

all external forces (excluding spring force and gravity)

all external forces, normally including spring force and gravity.


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