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Forces Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

what are forces

A

interactions between two objects that can be a push or a pull

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2
Q

what does a scalar quantity have

A

a magnitude and no direction

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3
Q

what does a vector quantity ahve

A

magnitude and an associated direction

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4
Q

how are vector quantities represented

A

by an arrow

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5
Q

what does the length of a vector arrrow represent

A

the magnitude

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6
Q

what does the direction of a vector arrow represent

A

the direction of the vector quantity

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7
Q

what does a contact force mean

A

the objects are physically touching

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8
Q

what does a non contact force mean

A

the objects are physically separated

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9
Q

examples of scalar quantities

A

mass
volume

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10
Q

examples of vector quantities

A

acceleration
force

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11
Q

examples of contact forces

A

friction
air resistance
tension
reaction force

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12
Q

examples of non contact forces

A

gravitational force
electrostatic force
magnetic force

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13
Q

what is weight

A

the force acting on an object due to gravity. the force of the gravity close to the earth is due to the gravitational field around the earth.

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14
Q

what does gravity effect

A

all things with mass

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15
Q

what does the weight of an object depend on

A

the gravitational field strength at the point where the object is

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16
Q

what is the equation for weight

A

weight = mass x gravity

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17
Q

what is weight measured in

A

N

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18
Q

what is gravitational field strength measured in

A

N/Kg

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19
Q

what is the link between weight and mass of an object

A

directly proportional

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20
Q

how is weight measured

A

calibrated spring balance (newton meter)

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21
Q

what is the resultant force

A

a single force that replaces a number of forces acting on an object but has the same effect as all the original forces acting together

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22
Q

what is newtons 1st law

A

if forces acting on an object are balanced then it will
be stationary
or be moving at a constant speed

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23
Q

when is work done on an object

A

when a force causes an object to move through a distance

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24
Q

why is an object displaced when a force is applied

A

it has done work

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25
Q

work done equation

A

force x distance

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26
Q

when is one joule of work done

A

when a force of one newton causes a displacement of one metre

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27
Q

what does one joule equal

A

one newton metre

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28
Q

what does work done against the frictional forces acting on an object cause

A

a rise in the temperature of the object

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29
Q

what is newtons 3rd law

A

forces normally act in pairs because two objects that interact with each other exert equal and opposite forces on eachother

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30
Q

what is the centre of mass of an object

A

the point at which its mass can be thought to be concentrated

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31
Q

where is the centre of mass of a regular shape found

A

where two lines of symmetry meet

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32
Q

when is an object in equilibrium

A

when the object is suspended

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33
Q

conditions for an object to be stable

A

the line of action of the force acts within the objects base

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34
Q

what is a pívot

A

a point at which a lever can rotate

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35
Q

what is a load

A

an object that moves

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36
Q

what is effort

A

force required to move the load

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37
Q

what is a lever

A

anything that can turn
levers are simple machines that can act as force multipliers

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38
Q

what causes a moment

A

because of the pívot point an applied force can cause a turning effect

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39
Q

units of a moment

A

newton metres or newton cm

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40
Q

what is the distance in the moment equation

A

perpendicular distance from the pívot to the line of action of the force

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41
Q

what causes a lever to be in equilibrium

A

the sum of the clockwise moments must be equal to the sum of anticlockwise moments

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42
Q

typical speed of a person walking

A

1.5m/s

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43
Q

typical speed of a person running

A

3m/s

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44
Q

typical speed of someone cycling

A

6m/s

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45
Q

typical value of speed of sound in air

A

330m/s

46
Q

what does the speed a person can walk run or cycle depend on

A

age, terrain, fitness, distance travelled

47
Q

what do gears act as

A

a force multiplier

48
Q

what does a low gear cause

A

low speed and a high turning effect

49
Q

what does a high gear give

A

high speed and a low turning effect

50
Q

how do you calculate speed

A

distance / time

51
Q

unit of speed

A

m/s

52
Q

what is velocity

A

an objects speed in a given direction

53
Q

how can two objects have the same speed but different velocities

A

they travel in opposite directions

54
Q

what happens if an object moves at a constant speed in a circle

A

its velocity is constantly changing even though its speed is constant

55
Q

how can the distance travelled be presented if an object moves along a straight line

A

a distance time graph

56
Q

what is acceleration

A

the change in velocity per second

57
Q

acceleration calculation

A

change in velocity / time taken

58
Q

acceleration units

A

m/s^2

59
Q

what is deceleration

A

when an object is slowing down

60
Q

constant acceleration equation

A

(final velocity)^2 - (initial velocity)^2 = 2 x acceleration x distance

61
Q

what is the acceleration of any object falling freely under gravity near the earths surface

A

9.8m/s^2

62
Q

why does an object falling through a fluid initially accelerate

A

the force of gravity

63
Q

what do distance time graphs show

A

how an objects distance varies within time

64
Q

where is time always plotted on a dt graph

A

x axis

65
Q

what is the gradient of a distance time graph

A

the speed

66
Q

what does a velocity time graph show

A

how the velocity of an object is changing with time

67
Q

what does the gradient of a velocity time graph show

A

the acceleration or deceleration of the object

68
Q

what does the area under a velocity time graph show

A

the distance travelled by the object

69
Q

what kind of quantity is distance

A

scalar

70
Q

what kind of quantity is speed

A

scalar quantity

71
Q

what kind of quantity is velocity

A

vector quantity

72
Q

what does displacement include

A

the distance an object moves and the direction of that straight line

73
Q

what kind of quantity is displacement

A

vector quantity

74
Q

what is newton’s second law

A

the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object

75
Q

what can a fluid be

A

a liquid or a gas

76
Q

what does pressure in fluids cause

A

a force normal (at right ángles) to any surface

77
Q

pressure at the surface of a fluid equation

A

force normal to a surface / area of that surface

78
Q

what is pressure measured in

A

Pa

79
Q

equation for pressure due to a column of liquid

A

height of the column x density of the liquid x gravitational field strenth

80
Q

where is the atmosphere most dense

A

the surface of the earth

81
Q

when does the atmosphere get less dense

A

when the altitude increases

82
Q

what happens as a surface increases height above ground level

A

the number of air molecules above the surface decreases

83
Q

what causes an object to inflate

A

when the air pressure outside of it is lower than the pressure inside of the object

84
Q

why does a partially or fully submerged object experience

A

a greater pressure on the bottom surface than on the top surface which created upthrust

85
Q

what creates atmospheric pressure

A

air molecules colliding with a surface

86
Q

how does depth affect pressure in a liquid

A

increases pressure

87
Q

why does a greater depth increase pressure

A

there is a greater weight of liquid acting downwards

88
Q

how does density affect pressure in a liquid

A

increases pressure

89
Q

what needs to happen for an object to float

A

the upthrust must equal the objects weight

90
Q

when does an object sink

A

if the upthrust is less than the objects weight

91
Q

what is the size of the upthrust acting on the object the same as

A

the weight of water displaced by the object

92
Q

what is the equation for force (2nd law)

A

force = mass x acceleration

93
Q

what is inertia

A

the tendency of an object to stay at rest or continue to move in a uniform motion

94
Q

what is the inertia of an object dependent on

A

its mass

95
Q

what is the stopping distance of a vehicle

A

the sum of the distance the vehicle travels during the drivers reaction time and the distance it travels under the braking force

96
Q

what is the thinking distance

A

the distance travelled by the vehicle during the drivers reaction time

97
Q

what is the braking distance

A

the distance travelled by the vehicle while the braking force is being applied

98
Q

what factors affect braking distance

A

road surface
speed
road conditions
mass of car
condition of tyres
condition of brakes

99
Q

what factors affect thinking distance

A

alcohol
tiredness
speed
age
visibility
drugs
distractions

100
Q

what are typical reaction times in humans

A

0.2s to 0.9s

101
Q

what can be caused by braking too fast

A

kinetic energy converted to thermal
can cause brakes to overheat
driver loses control of vehicle

102
Q

what is momentum

A

when a force acts on a body that is moving or able to move a change in momentum occurs

103
Q

what does momentum have

A

magnitude and direction

104
Q

momentum equation

A

mass x velocity

105
Q

momentum in a closed system

A

total momentum before an event is equal to the total momentum after the event

106
Q

what happens to momentum during a car crash

A

momentum of the passenger falls from a large amount to zero in less than a second

107
Q

what is an impact force

A

the force created when a change in momentum occurs

108
Q

impact force equation

A

change in momentum/ impact time

109
Q

what do rapid changes in momentum cause

A

huge dangerous forces being applied

110
Q

how can danger of impact forces be reduced

A

make change in momentum happen over a longer time

111
Q

what equipment can slow down momentum change

A

airbags
seatbelts
crashmat
bike helmet
cushioned surface

112
Q

how do safety features slow down momentum change

A

reduce forces acting which reduces risk of injury

Physics (19 decks)

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