CH 4-5-6 Flashcards

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1
Q

What weighs 1 N?

A

an apple

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2
Q

What weighs 10N?

A

Large Textbook (a 1 liter bottle of soda)

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3
Q

What weighs 100N?

A

3 Gallons of milk

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4
Q

What weighs 1000N?

A

Mr. Nystrom wearing a backpack full of books

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5
Q

If you weigh 600N and are hanging on a rope, you are pulling down 600N on the rope. The rope is pulling ______

A

up 600N on you!

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6
Q

If you weigh 600N and jump off of a building, do you accelerate towards the earth? Does the earth accelerate towards you?

A

YES, you accelerate toward the earth and YES the earth accelerates toward you (it is hard to see)

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7
Q

How can you think of gravity to help you “see” objects being pulled towards eachother?

A

Imagine a bungee between them. A bungee between two cars may pull them both together at the same acceleration, but a bungee between a car and a skateboard will mostly pull the skateboard more. MASS RESISTS ACCELERATION

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8
Q

Why don’t you see the earth move when you jump up?

A

It is so massive that it barely moves

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9
Q

If force = mass * acceleration, then acceleration =

A

FORCE / MASS

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10
Q

if force = mass * acceleration, then mass=

A

FORCE / ACCELERATION

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11
Q

When you fire a gun, the force on the bullet is equal to the _____________

A

force on the gun

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12
Q

why does a bullet go faster forward than the gun moves backwards if they have the same force?

A

the gun has more mass. If you push a roller skate with the same force that you push a bus, the rollerskate will accelerate faster! Mass resists acceleration.

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13
Q

What is a way to think of mass when it comes to movement?

A

MASS RESISTS ACCELERATION (this is what we call inertia)

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14
Q

How do you sketch the resultant force of two vectors?

A

USE THE PARALELLOGRAM RULE.

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15
Q

What does the delta (the little triangle) symbol mean?

A

It means “CHANGE IN”

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16
Q

What is Newton’s First Law?

A

Object stays at rest, or moves at a constant velocity in a straight line unless a force acts on it.

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17
Q

What is Newton’s Second Law?

A

F= ma Force increases acceleration, mass resists accelertion

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18
Q

What is Newton’s Third Law?

A

Every action (force) has an equal and opposite reaction

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19
Q

Give a quick summary of Newton’s three laws of motion:

A

FIRST: objects in motion or rest stay that way, SECOND: harder to push more massive objects , THIRD: action have equal opposite reactions

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20
Q

What are the three equations from newton’s second law? (my fish is from massachusetts)

A

a=F/m F= ma F/a = m

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21
Q

If you are given a force and an acceleration, you can find ____ by using the equation ____

A

mass, m= F/a

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22
Q

If you are given a mass and an acceleration, you can find ____ by using the equation ____

A

Force, F= ma

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23
Q

If you are given a force and a mass, you can find ____ by using the equation ____

A

a = F/m

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24
Q

Describe what NET force is

A

It is what is left after you combine all the forces (things cancel out).

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25
Q

How can we add two vectors (find resultant) by sketching?

A

Use the parallelogram rule, and the DIAGONAL is the resultant vector when both components start from the same spot.

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26
Q

How do we make sure our calculator is in the right mode?

A

press MODE> put cursor on DEGREES> press ENTER

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27
Q

What is the net force on an object at rest?

A

zero (not accelerating), but has potential energy!

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28
Q

What is the net force on an object moving at a constant velocity? Why?

A

zero (not accelerating) but has kinetic energy!

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29
Q

What has to be happening in order for net force to not be zero?

A

it must be ACCELERATING (changing velocity). just moving is not enough, it has to be changing speeds!

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30
Q

block on inclined plane: What is Fd and FN?

A

Fd is directional force DIAGONAL down plane along the slope, FN is normal force directly into the plane

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31
Q

Explain what Fd is in plain terms

A

Directional force, it is the force that acts on the block pushing it down the ramp. it goes diagonally down the ramp, parallel to the ramp.

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32
Q

Explain Fn in plain terms

A

It is the squeeze force between the block and the ramp. It measures the force going directly perpendicular into the plane. It is in the direction of an upside down thumb tack.

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33
Q

How can remember the direction of the normal force?

A

a thumb tack on its back. the pointy side is in the direction of the normal force.

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34
Q

Directional force (down along the plane) is:

A

Fd

It is directional, or down the plane, parallel to the plane, along the plane

35
Q

The force between the block and the ramp is

A

the normal force, Fn (the squeeze force)

36
Q

If you have weight, how do you find normal force?

A

w*cos (angle) gives normal force. “COS it’s normal”

37
Q

If you have weight, how do you find directional force?

A

w*sin(angle) gives the directional force. “SINES GIVE DIRECTIONS”

38
Q

What do we use normal force to calculate?

A

FRICTION. it is the squeeze force since it is the measure of the force between the block and the plane, it determines amount of friction. Friction=FN * Mu

39
Q

The force of friction always acts____

A

in the opposide direction of motion

40
Q

You can calculate the force of friction by multplying ____ by ____

A

normal force by coefficient of friction

41
Q

Coefficients of friction are _____ for surfaces that are smooth and ____ for surfaces that are rough, or sticky.

A

smaller, larger

42
Q

What is the unit of force we use?

A

NEWTON

43
Q

What is the unit of weight we use?

A

NEWTON

44
Q

what is a NEWTON a unit for?

A

for FORCE and WEIGHT (weight is a force)

45
Q

What are the units in a NEWTON?

A

kg*m/s2 (notice it it a mass * acceleration)

46
Q

what are the units we use for acceleration?

A

m/s2

47
Q

What are the units we use for mass?

A

kg

48
Q

a newton (F) divided by acceleration (a) (m/s2) will give you

A

mass (kg)

49
Q

a newton (F) divided by a mass (m) (kg) will give you

A

an acceleration (m/s2)

50
Q

a mass (m)(kg) multiplied by an acceleration(a) (m/s2) will give you

A

a newton (force)

51
Q

is mass a force? explain

A

No. to be a force you need a mass AND acceleration. Mass is a scalar quantity and has no direction. Force is a vector.

52
Q

is weight a force? explain

A

YES. F=ma, W=mg. gravity is an acceleration, so when you do mass times gravity, that is the same as mass times acceleration.

53
Q

How much does a 3kg object weigh?

A

about 30N

54
Q

Is acceleration scalar or vector?

A

vector (has direction and magnitude)

55
Q

What is the mass of a 35N object?

A

3.5 kg

56
Q

What is acceleration when 12N is applied to 3kg object? Why?

A

4 m/s2. Since F=ma, then a=F/m so 12N/3kg = 4m/s2

57
Q

What is the net force on a 10kg object that is accelerating at 2 m/s2

A

F = ma so 10(2) = 20N

58
Q

What is the mass of an object that acceleraties 5 m/s2 when a 30N force is applied?

A

m= F/a so 30/ 5 = 6kg

59
Q

What force do you need to accelerate a 1000kg car 5 m/s2 ? (ignore friction)

A

5000N

60
Q

What will the acceleration be of an 800kg car that is pushed with a force of 8000N? (ignore friction)

A

10m/s2

61
Q

What is terminal velocity?

A

the highest speed a falling object will reach because of air resistance

62
Q

What is the net force on an object that is moving at its terminal velocity? Explain

A

zero. it is not accelerating

63
Q

What receives a greater force of air resistance, an elephant or a feather falling? Why?

A

elephant. it is pushing through more air

64
Q

What is the difference between mass and weight?

A

mass is the amount of stuff, mass is a measure of resistance to change, weight is the force due to gravity on the planet it is on

65
Q

Which is more stable, mass or weight? Explain

A

mass is same on earth or moon, weight changes on different planets with diff gravity. Also, you weigh less on a plane than on the ground (gravity decreases the further from earth you are)

66
Q

Give an example of Newton’s first law in real life:

A

an apple on a desk. net force is zero, until you push it off (things at rest or motion stay that way)

67
Q

Give an example of Newton’s second law in real life:

A

harder to push a car than to push a skate board (mass resists acceleration, f=ma)

68
Q

Give an example of Newton’s third law in real life:

A

the floor is pushing up on you as much as you are pushing down on the floor (equal and opposite)

69
Q

Do you weigh more on the ground or in an airplane?

A

On the ground. The further from an object, the less its gravitational pull influences you.

70
Q

An object in equilibrium is

A

standing still or moving at a constant velocity.

71
Q

if there is a net force then the object must be

A

accelerating.

72
Q

if an object is moving, must there be a force on it?

A

NO. it can be moving at a constant velocity with no force, if it’s velocity changes, then there must be a force present.

73
Q

A 60N object has a _________

A

mass of 6kg

74
Q

A 55kg object has a _______

A

weight of 550N

75
Q

2.5N= ___kg

A

.25kg

76
Q

2.5kg=___N

A

25N

77
Q

if a force acts in the same direction as the velocity, then the object will

A

speed up (positive acceleration)

78
Q

if a force acts in the opposite direction as the velocity then the object will

A

slow down (negative acceleration, or deceleration)

79
Q

what is terminal velocity?

A

when the force of air resistance is equal to the weight ( weight is the force due to gravity). It is in equilibrium.

80
Q

what happens when an object reaches terminal velocity?

A

It stops accelerating. It has reached its top speed and it just continues down at a constant velocity.

81
Q

What is the net force of an object moving at its terminal velocity?

A

zero. No acceleration.

82
Q

If something is slowing down, then it is accelerating in the ________ direction

A

opposite.

83
Q

If something is speeding up, then it is accelerating in the ____ direction,

A

same

84
Q

if a problem says “constant velocity” that means that the acceleration is ____ and the net force is _____

A

the acceleration is zero and the net force is zero.