# forces

0.0 / 5

- Created by: ellie_225
- Created on: 20-05-18 11:07

what is a scalar

magnitude only.

1 of 132

what is a vector

have magnitude and an associated direction

2 of 132

what can vectors be represented by

an arrow. The length of the arrow represents the magnitude, and the direction of the arrow the direction of the vector quantity.

3 of 132

examples of scalars

temperature, distance, speed, time, mass, energy, power

4 of 132

examples of vectors

Force, weight, displacement, velocity, acceleration, momentum,

5 of 132

drawing vectors

You can represent a vector using an arrow. The length of the arrow shows the magnitude of the vector. The direction of the arrow shows the direction of the vector quantity.

6 of 132

what is a force

A force is a push or pull that acts on an object due to the interaction with another object. All

7 of 132

contact force

the objects are physically touching e.g. include friction, air resistance, tension and normal contact force.

8 of 132

non contact force

the objects are physically separated. e.g. gravitational force, electrostatic force and magnetic force.

9 of 132

what is a resultant force

A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together. This single force is called the resultant force.

10 of 132

can a single force be resolved into two components

A single force can be resolved into two components acting at right angles to each other. The two component forces together have the same effect as the single force.

11 of 132

how can the size of the resultant force be found

by using geometry or by making a scale drawing and measuring it.

12 of 132

resolving a force

force involves finding 2 perpendicular forces that have a resultant force which is the same as the original force. Forces are usually resolved in to horizontal and vertical components.

13 of 132

balanced forces

equal in size and opposite in direction

14 of 132

what happens if forces are balanced

there is no resultant force. The object will continue doing whatever it is doing. It will stay still or continue moving at a constant velocity.

15 of 132

what happens if the forces are unbalanced

there is a resultant force. The object will accelerate (change direction) in the direction of the unbalanced force.

16 of 132

gravity

Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth. • The weight of an object depends on the gravitational field strength at the point where the object

17 of 132

weight =

mass x gravitational field strength

18 of 132

weight equation units

weight, W, in newtons, N mass, m, in kilograms, kg gravitational field strength, g, in newtons per kilogram, N/kg

19 of 132

center of mass

The weight of an object may be considered to act at a single point

20 of 132

weight and mass

The weight of an object and the mass of an object are directly proportional.

21 of 132

what is weight measured in

using a calibrated spring-balance (a newtonmeter).

22 of 132

what is mass

is a measure on the amount of matter in an object. It is measured in kg.

23 of 132

work done

When a force causes an object to move through a distance work is done on the object. So a force does work on an object when the force causes a displacement of the object.

24 of 132

work done =

force x distance moved along the line of action of the force

25 of 132

what is the same as 1 joule

One joule of work is done when a force of one newton causes a displacement of one metre

26 of 132

work done against the frictional forces acting on an object can cause a

rise in the temperature of the object

27 of 132

power is the rate

at which energy is transferred. A powerful machine can do work and transfer energy quickly.

28 of 132

The extension of an elastic object, such as a spring, is directly proportional

to the force applied, provided that the limit of proportionality is not exceeded

29 of 132

force =

spring constant x extension

30 of 132

force equation units

force, F, in newtons, N spring constant, k, in newtons per metre, N/m extension, e, in metres, m

31 of 132

a force that strenches or compressed

a spring does work and elastic potential energy is stored in the spring. Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential energy stored are equal.

32 of 132

elastic potential energy =

0.5 x specific constant x extension2

33 of 132

elastic stretch

Elastic materials can be stretched or squashed and then return to their original shape. Plastic materials are permanently deformed when a force is applied to them.

34 of 132

what happens when the force is applied

If a force is applied to a spring, the spring stretches. The extension is the new length minus the original length When the spring is stretched it stores elastic potential energy. It returns to its original length when the load is removed.

35 of 132

the extension is the length -

original length

36 of 132

extension graph

The first section of the graph of extension against load is a straight line through the origin. This shows that extension is proportional to load. The spring obeys Hooke's Law.

37 of 132

hookes law

The extension of a spring is directly proportional to the load, provided the limit of proportionality has not been exceeded.

38 of 132

if a large load is applied to the spring

it exceeds the elastic limit. If the load is removed the spring will not return to its original length - it is permanently deformed.

39 of 132

do elastic bands obey hookes law

Elastic bands do not obey Hooke's Law. A graph of extension against load is curved.

40 of 132

do metal wires obey hookes law

Metal wires obey Hook's Law, but will reach a point where they stretch rapidly and then break.

41 of 132

the extension of a spring is proportional to

the load as long as the limit of proportionality is not exceeded. • This means a graph of load against extension is a straight line through the origin. • The equation of the graph is of the form F = kx where k is a constant.

42 of 132

force =

spring constant x extension

43 of 132

what does a large spring constant mean

that it requires a large force to stretch the spring so the spring is ‘stiff’.

44 of 132

what happens when a spring is streached

work is done on it by the load. This means that energy is transferred to it. This is (stored) elastic potential energy.

45 of 132

what is a force

A force or a system of forces may cause an object to rotate

46 of 132

what is the turning effect

The turning effect of a force is called the moment of the force.

47 of 132

moment of a force =

distance x force

48 of 132

turning effect - what if an object is balalnced

If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.

49 of 132

center of gravity

¥ The mass of an object can be thought of as being concentrated at a point. ¥ This point is called the centre of gravity or mass. ¥ The weight of a body acts through the centre of gravity

50 of 132

to find the centre of gravity of an irregular object

1. Make a small hole in the card 2. Suspend the card from a long pin 3. Suspend a plumb-line from the pin. 4. Mark the position of the plumb-line on the card 5. Repeat 2 or 3 times 6. The centre of gravity is where the lines cross

51 of 132

middle of a regular shape

¥ If the card is a regular shape, the centre of gravity will be on the axis of symmetry. ¥ It should be possible to balance the card at the centre of gravity

52 of 132

stability

When an object is tilted ¥ If the centre of gravity is over the base of the object, the object will return to its original position (a). It is stable ¥ If the centre of gravity is outside the base, the object will topple over (C). It is unstable.

53 of 132

moments

¥ A moment is the turning effect of a force ¥ Moments are measured in Nm ¥ Perpendicular means at right angles

54 of 132

moment of force =

force x perpendicular distance from the pivot

55 of 132

if an object is balanced

If an object is balanced (in equilibrium) then the moments turning it in one direction must cancel out the moments in the other direction.

56 of 132

anticlockwise moments =

clockwise moments

57 of 132

what do levers and gears emit

these both transmit rotational forces

58 of 132

levers as force multipliers

If d2 is much larger than d1, F2 will be much smaller than F1 .

59 of 132

gears

The pedals turn a gear which transmits the force to the wheels. The different number of teeth on the gear make the greas combination into a force multiplier. You put the bike in a low gear to go up hill, where you need lots fo force, but move slowly.

60 of 132

gears 2

On the flat, you put the bike in a high gear so that you can move fast, but you don’t need so much force.

61 of 132

pressure in fluids

• A fluid can be either a liquid or a gas. • The pressure in fluids causes a force normal (at right angles) to any surface. The pressure at the surface of a fluid can be calculated using the equation:

62 of 132

pressure =

force normal to a surface / areas of that surface

63 of 132

what is pressure

Pressure is a measure of how spread out a force is • Pressure is measured in N/cm2 or N/m2 • 1 N/m2 = 1 Pascal (Pa)

64 of 132

pressure =

height of the column x density of the liquid x gpe

65 of 132

A partially (or totally) submerged object experiences

greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. This force is called the upthrust.

66 of 132

what is a fluid

liquid or gas

67 of 132

how is pressure in a fluid caused

by the particles bumping in to each other and their container and exerting a force on it.

68 of 132

the atmosphere

The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude.

69 of 132

what creates atmospheric pressure (ap)

molecules colliding w/ surface create ap. The no. of air molecules above a surface decreases as the height of the surface above ground level +. height increases there is always less air above a surface than their is at lower height.

70 of 132

general atmospheric pressure

atmospheric pressure decreases with an increase in height.

71 of 132

what is distance

Distance is how far an object moves. Distance does not involve direction. Distance is a scalar quantity.

72 of 132

what is displacement

Displacement includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line. Displacement is a vector quantity.

73 of 132

is displacement and distance vectors or scalars

Distance is a scalar and has size; displacement is a vector and has both size and direction.

74 of 132

is speed a scalar

Speed does not involve direction. Speed is a scalar quantity.

75 of 132

is speed constant

The speed of a moving object is rarely constant. When people walk, run or travel in a car their speed is constantly changing

76 of 132

what factors affect speed

The speed at which a person can walk, run or cycle depends on many factors including: age, terrain, fitness and distance travelled.

77 of 132

what things vary in speed

It is not only moving objects that have varying speed. The speed of sound and the speed of the wind also vary.

78 of 132

value of sound

330n m/s

79 of 132

for constant speed - distance =

speed x time

80 of 132

velocity of an onject

is its speed in a given direction. Velocity is a vector quantity

81 of 132

do objects travel at a constant speed

no. For example a car will speed up and slow down depending on road conditions.

82 of 132

if an object moves along a straight line

the distance travelled can be represented by a distance–time graph.

83 of 132

if an object is accelerating

If an object is accelerating, its speed at any particular time can be determined by drawing a tangent and measuring the gradient of the distance–time graph at that time.

84 of 132

how can speed be found from a graph

The speed can be found from the gradient of the graph. • Where the graph is horizontal, the object is not moving

85 of 132

if the speed is changing

find the instantaneous speed by drawing the tangent to the curve and then finding the gradient of the tangent.

86 of 132

the average acceleration =

change in velocity / time taken

87 of 132

an object that slows down

is decelerating

88 of 132

how can the distance travelled by an object be calculated

area under a velocity–time graph.

89 of 132

final velocity2 - initial velocity2

2 x acceleration x distance

90 of 132

acceleration

Acceleration is the rate of change of speed

91 of 132

What does it mean if the graph is steeper

the higher the acceleration, so the object is speeding up.

92 of 132

Acceleration on the graph

is the gradient of the graph? If the gradient is negative, the object is slowing down.

93 of 132

What does the horizontal part of the graph show

the object is moving at a constant velocity (speed)

94 of 132

how can the distance travelled?

from the area under the graph. If the graph is horizontal, you can use distance = speed x time, but if the graph slopes, the speed is changing so you must find the area.

95 of 132

you can use an equation if the acceleration is constant

Final velocity2 = initial velocity2 –2 x acceleration x displacement

96 of 132

Newton’s First Law:

If the resultant force acting on an object is zero and the object is stationary, the object remains stationary the object is moving, the object continues to move at the same speed and in the same direction. the object continues to move at the same v

97 of 132

Newton’s law in a vehicle

when a vehicle travels at a steady speed, the resistive forces balance the driving force. the velocity (speed and/or direction) of an object will only change if a resultant force is acting on the object.

98 of 132

Newton’s First Law on an object

An object at rest stays at rest + object that is moving continues to move at a constant speed, unless acted on by an unbalanced force. If balanced, so that the resultant force is zero it will continue to move with constant speed and direction

99 of 132

Newton's Second Law

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

100 of 132

Equation of second law

resultant force = mass x acceleration

101 of 132

units for resultant force

force, F, in newton’s, N mass, m, in kilograms, kg acceleration, a, in metres per second squared, m/s2

102 of 132

what happens If the forces on an object are balanced,

the resultant force is zero and it will continue moving at a constant speed. If it is not moving, it will remain stationary.

103 of 132

What happens If the forces on an object are unbalanced,

the object will accelerate in the direction of the resultant force.

104 of 132

What is the acceleration near the earth surface

Near the Earth’s surface any object falling freely under gravity has an acceleration of about 9.8 m/s2.

105 of 132

Objects falling through a fluid

initially accelerates due to the force of gravity. Eventually the resultant force will be zero and the object will move at its terminal velocity.

106 of 132

What is the drag force caused by?

the drag force is caused by air resistance. the faster an object falls, the larger the air resistance the weight of the falling object does not change

107 of 132

Newton's Third Law

Whenever two objects interact, the forces they exert on each other are equal and opposite.

108 of 132

Stopping distance of vehicle

is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) + the distance travels under the braking force. For a given braking force the greater the speed of the vehicle, the + the stop distance

109 of 132

Reaction time

Reaction times vary from person to person. Typical values range from 0.2 s to 0.9 s. A driver’s reaction time can be affected by tiredness, drugs and alcohol. Distractions may also affect a driver’s ability to react.

110 of 132

The braking distance of a vehicle can be affected

by adverse road and weather conditions and poor condition of the vehicle.Adverse road conditions include wet or icy conditions. Poor condition of the vehicle is limited to the vehicle's brakes or tyres.

111 of 132

When a force is applied to the brakes of a vehicle

, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases.

112 of 132

The greater the speed of a vehicle the greater

the braking force needed to stop the vehicle in a certain distance.

113 of 132

The greater the braking force the greater

the deceleration of the vehicle. Large decelerations may lead to brakes overheating and/or loss of control.

114 of 132

Thinking distance

is the distance the car moves while the driver is thinking about pressing the brake. It is the distance travelled during the driver's reaction time.

115 of 132

Thinking distance increases if:

the car is going faster - the driver is tired - the driver has had alcohol or drugs the driver is distracted (egg mobile phone)

116 of 132

Braking distance

is the distance the car moves after the brakes have been pressed

117 of 132

Braking distance increases if:

the car is going faster - the car is heavier - the car brakes are worn - the car tyres are worn - the road surface is slippery, egg ice, rain,

118 of 132

stopping distance =

thinking distance + braking distance

119 of 132

what happens for stopping distance

• When the brakes are on, the car slows down, because of friction. • Kinetic energy is transferred to thermal energy in the surroundings. • Work is done by friction so energy is transferred.

120 of 132

the faster the car is travelling

more kinetic energy it has and so the more energy that must be transferred. More work must be done, so the braking force must act over a longer distance

121 of 132

momentum =

mass x velocity

122 of 132

In a closed system, the total momentum before an event is equal

to the total momentum after the event. This is called conservation of momentum.

123 of 132

Units for momentum:

kg m/s

124 of 132

is momentum a vector

Momentum is a vector quantity – the direction is important

125 of 132

Conservation of momentum:

The total momentum of a closed system in a specific direction remains constant as long as no external forces act on the system.

126 of 132

What happens when two objects collide

the total momentum before the collision is the same as the total momentum afterwards.

127 of 132

Elastic and inelastic collisions

• In any collision momentum and total energy are conserved • In a perfectly elastic collision the kinetic energy is conserved • In an inelastic collision, kinetic energy is not conserved

128 of 132

Changes in momentum

When a force acts on an object that is moving, or able to move, a change in momentum occurs.

129 of 132

force =

rate of change of momentum.

130 of 132

examples of momentum:

1. Crash helmets, crumple zones on cars, seat belts that stretch slightly. These all: • increase the time it takes an object to stop and so • reduce the force needed • to give the same change in momentum.

131 of 132

examples of momentum: 2

Hitting a golf ball or tennis ball hard To get the largest effect from a given force you follow through with the hit so that you: • Increase the time the force is exerted on the ball which • Increases the change in momentum • For a given force

132 of 132

## Other cards in this set

### Card 2

#### Front

what is a vector

#### Back

have magnitude and an associated direction

### Card 3

#### Front

what can vectors be represented by

#### Back

### Card 4

#### Front

examples of scalars

#### Back

### Card 5

#### Front

examples of vectors

#### Back

## Related discussions on The Student Room

- intramolecular forces and intermolecular forces »
- when do you use the term overcome forces and break forces ... »
- does phospine PH3 form permanent dipole- dipole forces or ... »
- M1 Forces past paper question »
- M1 Forces question »
- Armed Forces Communication »
- Keratoconus and the armed forces? »
- Armed Forces »
- Eyesight for HM Armed Forces »
- Graphical Method of magnitude and nature of internal forces. »

## Similar Physics resources:

1.0 / 5

0.0 / 5

2.5 / 5

0.0 / 5

0.0 / 5

3.0 / 5

0.0 / 5

0.0 / 5

1.0 / 5

0.0 / 5

## Comments

No comments have yet been made