5. Forces Flashcards Preview

AQA GCSE Physics (9-1) > 5. Forces > Flashcards

Flashcards in 5. Forces Deck (121):
1

What is a scalar?

Quantities that are fully described by magnitude or size

2

What are vectors?

Quantities that are fully described by both a magnitude and direction

3

What is distance?

A scalar quantity that refers to 'how much ground an object has covered'

4

What is displacement?

A vector quantity that refers to 'how far out of place an object is'

5

What is magnitude?

Size

6

How can vectors be drawn?

Using arrows

7

Is time a vector or scalar quantity?

scalar

8

Is force a vector or scalar quantity?

Vector

9

Is friction a vector or scalar quantity?

Vector

10

Is weight a vector or scalar quantity?

Vector

11

Is displacement a vector or scalar quantity?

Vector

12

Is distance a vector or scalar quantity?

Scalar

13

Is density a vector or scalar quantity?

Scalar

14

Is energy a vector or scalar quantity?

Scalar

15

Is frequency a vector or scalar quantity?

Scalar

16

Is mass a vector or scalar quantity?

Scalar

17

Is power a vector or scalar quantity?

Scalar

18

Is voltage a vector or scalar quantity?

Scalar

19

Is volume a vector or scalar quantity?

Scalar

20

What is the gradient on a distance-time graph?

Velocity

21

What is the gradient on a velocity-time graph?

Acceleration

22

What is the area under a velocity-time graph?

The distance

23

What is acceleration?

When an object speeds up or changes direction

24

What is the total area underneath a velocity-time graph?

The total distance travelled

25

What is the unit of force?

Newtons, N

26

Examples of contact forces?

• Friction

• Air / Water resistance (drag)

• Normal contact (reaction)

• Tension

• Upthrust

27

Examples of non-contact forces?

• Gravity

• Magnetic

• Electrostatic

28

What happens when the resultant force on an object is zero?

The object remains stationary or continues to move at a constant speed and in the same direction.

29

What is enersher?

The idea that without an unbalanced force, nothing will change in terms of speed, direction etc.

30

What is Newton's 1st law of motion?

An object will remain at rest or at a constant velocity unless there is a resultant force acting on it.

31

What is Newton's 2nd law of motion?

The acceleration of an object is directly proportional to the resultant force and inversely proportional to the objects mass.

32

What equation shows Newtons 2nd law of motion?

F = m a

33

What is Newton's 3rd law of motion?

If object A exerts a force on object B, then object B exerts a force on object A which is equal and opposite.

34

How is inertial mass defined?

By the ratio of force over acceleration

(if an object is more inert then it's harder to move)

35

What is thinking distance proportional to?

Speed

36

What is braking distance proportional to?

Speed2

37

What is thinking distance?

The distance travelled during reaction time.

38

What is braking distance?

The distance travelled while the brakes are applied.

39

Why does thinking distance increase?

• the speed increases

• the reaction time increases eg. tiredness, distraction, taken drugs / alcohol

40

When does braking distance increase?

If the initial speed increases or if the size of deceleration is less.

41

How is thinking distance decreased?

Friction reduced - wet roads, worn tyres or brakes

42

How is braking distance decreased?

Larger mass of car (more inertia means its harder to stop)

43

How is thinking distance shown on a graph?

Area of the rectangle underneath the graph

44

How is braking distance shown on a graph?

Area of the triangle underneath the graph

45

Typical speed of walking?

1.5 m/s

46

Typical speed of running?

12 m/s

47

Typical speed of driving?

20 m/s

48

Typical speed of flying?

200 m/s

49

Speed of sound in air?

3x10 squared

50

Speed of light?

3x10 to the 8

51

What is the weight of an object?

The force of gravity on it

52

How to convert from Kg to N?

x10

53

When does an object reach constant velocity?

When the drag force is equal and opposite to its weight

54

What is terminal velocity?

When an object reaches a constant velocity because the drag force is equal and opposite to its weight

55

What happens to the drag force when an object is released in a fluid before its terminal velocity?

The drag force is less than its weight before it reachers terminal velocity

56

What happens to acceleration when an object is released in a fluid after its terminal velocity?

It is equal to zero

57

What happens to the resultant force on an object released in a fluid initially?

The resultant force is equal to its weight, initally

58

When an object is falling, what does it initially accelerate at?

10 m/s2

59

What are plastic objects?

Objects that do not regain their original shape when the forces deforming it are removed

60

What are elastic objects?

An object that regains its original shape when the forces deforming it are removed

It stores elastic potential energy when work is done on the object

61

Does an elastic collision lose kinetic energy?

No

62

What does Hooke's law state?

That the extension of a spring is in direct proportion with the force applied to it

63

What is the spring extension?

New length - original length

64

What does hooke's law only apply to?

Elastic materials

65

What happens to a spring if the force added on the spring is larger?

It not longer obeys hooke's law and does not return to its original length

66

What is elastic limit?

The limit of proportionality (when hooke's law no longer applies)

67

What is stopping distance?

Thinking distance + braking distance

68

What are the two SUVAT equations?

v = u + at

v2 = u2 - 2as

69

What are the two ways of increasing the turning effect of a force?

• increase the size of the force

• increase the distance from the pivot

70

What is the turning effect of a force called?

A moment

71

What is the equation to calculate the size of a moment?

M=Fd

72

What are moments measured in?

Nm

73

When will a seesaw balance in terms of moments?

When the anticlockwise moment is equal to the clockwise one

74

What does the principle of moments state?

For a balanced object, clockwise moments = anticlockwise moments

75

What is the centre of mass of an object?

The point at which the mass may be thought to be concentrated

76

Where does the centre of mass lie in symmetrical objects?

Along the line of symmetry

77

Where will the COM be when an object has more than one line of symmetry?

Where the lines of symmetry intersect

78

Where will the centre of mass be of a suspended object?

The centre of mass will be directly below the point of suspension

79

How can the COM of an irregular shape be found?

• by hanging the shape from a point and a plumb line is used to draw a vertical line downwards from the pivot

• this is repeated from different points

80

What is the stability of an object affected by?

• the width of the base of the object

• the height of it's centre of mass

81

When will an object not topple over?

When the line of action is within the base

82

What are the three types of equilibrium when a force is applied to objects?

• stable equilibrium - tilts and falls back to original position

• unstable equilibrium - tilts and falls

• neutral equilibrium - rolls

83

What happens to the centre of mass when a stable object is tilted?

It is raised

84

What happens to the centre of mass when an unstable object is tilted?

It is lowered

85

What happens to the centre of mass when a neutral object is tilted?

It stays at the same level if pushed

86

What does the pressure of a liquid depend on?

The depth and the density

87

What is the equation for the pressure at a certain depth due to the column of liquid?

pressure = depth x field strength x density

88

What is the nature of liquid pressures at different places, but at the same depth?

The pressure acts in all directions and is the same depth

89

What is the nature of liquid pressures at different depths?

The greater depth, the higher the pressure so the water is pushed down with a greater force and has a bigger horizontal range

90

What is a gear?

A rotating machine with cogs that mesh with another toothed part to transmit a moment

91

What do gears act as?

A force multiplier

92

What is a force multiplier?

Machines designed to increase the size of the force

93

What is a distance multiplier?

Machines designed to increase the distance or speed with which something moves

94

What effort and load do force multipliers involve?

• small effort (input force)

• larger load (output force)

95

Equation for mechanical advantage?

load / effort

96

Example of a force multiplier?

Lever with a distance from pivot to effort 3 times greater than distance from pivot to load - mechanical advantage is 3

97

How is a bike an example of a distance or speed multiplier?

Slow movement of pedals produces a much faster rotation of the wheels

98

What effort and load do distance multipliers involve?

• small movement of effort

• large movement of load

99

How is energy shown to be conserved in gears?

Work done by input gear = Work done by output gear

100

Why can a machine not be a force and distance multiplier at the same time?

As energy is conserved, if force is doubled the distance is halved and vice versa

101

What are levers used to do?

Lift heavy masses with the least amount of effort

102

What three things can gears do when passing power from one wheel to another?

• increase speed - first gear has more teeth than second so second has to turn faster to keep up

• increase force - second gear has more teeth than first so second turns slower but with more force

• change direction - when gears mesh they always turn in the opposite direction

103

In a hydraulic system, a smaller force on the master (effort) piston will produce what force on the slave (load) piston?

A larger force as the pressure of the liquid is constant - acting as a force multiplier

104

What is the ratio of in levers?

Lengths

105

What is the ratio of in gears?

Number of teeth

106

What is the ratio of in hydraulics?

Cross sectional areas

107

Equation for levers?

Fb/Fa = Lb/La

108

Equation for gears?

Fb/Fa = Nb/Na

109

Equation for hydraulics?

Fb/Fa = Ab/Aa

110

What is the atmosphere?

A thin layer of air around the earth

111

What happens at a greater altitude?

• the less dense the atmosphere

• the lower the atmospheric pressure

112

Why is the atmospheric pressure lower at greater altitudes?

• at higher altitudes there is less air above a surface

• so there is a smaller weight of air acting on the surface

• p=F/A and F is reduced so p will be smaller

113

How is upthrust created?

When the bottom surface of an object is submerged in a liquid it experiences a greater pressure than the top surface

114

When does an object float?

When its weight = upthrust / weight of fluid displaced

115

What is upthrust equal to?

The weight of the liquid displaced

116

What is the equation for momentum?

Mass x velocity

117

What is momentum measured in?

kgm/s

118

Why will a ball be harder to stop if it has a large mass and moving at a high speed?

There will be a greater force exerted on the person's hands by the ball. They will have to exert an equal and opposite force on the ball to stop it

119

What happens to momentum in a collusion of explosion?

Momentum is conserved, provided that there are no external forces having an effect

120

What are the external forces that could have an effect on momentum?

• friction which decreases momentum

• gravity (e.g. a collision on a slope)

121

What does force equal in terms of the change in momentum?

Force = change in momentum / time taken