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Forces Flashcards

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1
Q

What are scalar quantities

A

Have magnitude(size) only

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2
Q

What are vector quantities

A

Have magnitude and direction

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3
Q

Describe how a vector quantity is represented

A

By an arrow
The length of the arrow represents magnitude
Direction of the arrow represents direction of vector

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4
Q

Give examples of scalar quantities

A

Mass
Speed
Distance
Energy
Time
Temperature

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5
Q

Give examples of vector quantities

A

Displacement
Weight
Force
Velocity
Acceleration
Momentum

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6
Q

What is a force

A

A push or pull that acts on an object due to interaction with another object

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7
Q

What are contact forces

A

The objects are physically touching

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8
Q

What are non-contact force

A

The objects are physically separated

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9
Q

Examples of contact forces

A

Friction
Air resistance
Tension
Normal contact force

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10
Q

Examples of non-contact forces

A

Gravitational force
Electrostatic force
Magnetic force

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11
Q

What is weight

A

The force acting on an object due to gravity
The weight of an object depends on the gravitational field strength at the point where the object is

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12
Q

What is the equation linking mass, gravitational field strength, and weight

A

Weight (N) = Mass (kg) x gravitational field strength (N/kg)

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13
Q

What is the relationship between weight and mass

A

Directly proportional

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14
Q

How is weight measured

A

Using a calibrated spring-balance

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15
Q

What is ‘centre of mass’

A

The single point where the weight of an object acts on

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16
Q

What is a resultant force

A

A single force that has the same effect as all of the original forces acting together

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17
Q

What is work done

A

When a force causes an object to move through a distance work is done on the object

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18
Q

What is the equation that links force, work done, and distance

A

Work done (J) = force (N) x distance (m)

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19
Q

1 joule is equal to how many newton-meters

A

1 newton-metre

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20
Q

Describe the energy transfer when work is done when a car brakes

A

When brake presses against the wheel the force of friction now acts between the brake and the wheel
The kinetic energy store of the car is transferred to thermal energy store of the brakes
So temperature of brakes increase
So the car slows down as it loses kinetic energy

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21
Q

What is elastic deformation

A

When an object is stretched but can still return to its original size

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22
Q

What is inelastic deformation

A

When an object is stretched but does not return to its original size

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23
Q

What is the equation linking spring constant, force, extension

A

Force (N) = spring constant (N/m) x extension (m)

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24
Q

Describe the relationship between extension and force

A

The extension of an elastic object is directly proportional to the force applied provided that the limit of proportionality is not exceeded

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25
Q

Describe the effect of work done on a spring on the elastic potential energy store in the spring

A

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

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26
Q

What is the moment of a force

A

The turning effect of a force

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27
Q

What is the equation for the moment of a force

A

Moment of a force (Nm) = Force(N) X Distance(m)

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28
Q

What is the unit for moment

A

Newton-metre(Nm)

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29
Q

When is this true: the total clockwise moment about a pivot equals the total anti-clockwise moment about that pivot

A

When an object is balanced

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30
Q

What is a fluid

A

A liquid or gas

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31
Q

What is the equation for pressure

A

Pressure(Pa) = force normal to a surface(N) / area of that surface(m2)

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32
Q

What is the unit of pressure

A

Pascal (Pa)

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33
Q

What is the atmosphere

A

A thin layer of air around the earth
The atmosphere gets less dense with increasing altitude

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34
Q

How is atmospheric pressure created

A

Air molecules colliding with a surface

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35
Q

Explain how atmospheric pressure decreases with an increase in height

A

The number of air molecules above a surface decreases as the height of the surface above ground level increases.
So as height increases there is always less air above a surface than there is at a lower height

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36
Q

What is the equation for the pressure due to a column of liquid

A

Pressure (Pa) = height of column(m) X density of liquid(kg/m3) X gravitational field strength (N/kg)

37
Q

Why does pressure of a liquid increase with depth

A

As the depth increases there is a greater weight of liquid acting downwards

38
Q

Explain why pressure of a liquid increases with the density of the liquid

A

Liquids with a greater density have a greater weight acting downwards

39
Q

What is upthrust

A

A partially(or fully) submerged object experiences a greater pressure on the bottom surface than on the top surface
This creates a resultant force upwards
This force is called upthrust

40
Q

How does an object float

A

The upthrust is equal to the objects weight

41
Q

How does an object sink

A

When the upthrust is less than the object’s weight

42
Q

The size of the upthrust acting on the object is the same as…

A

The weight of water displaced by the object

43
Q

What happens when an object displaces its own volume of water

A

The weight of water displaced is equal to the weight of the object
So the object floats

44
Q

Why does an object more dense than water sink

A

The object cannot displace a volume of water equal to its own weight
So the weight of the object is greater than upthrust so the object sinks

45
Q

What is distance

A

How far an object moves
Distance does not involve direction
It’s a scalar quantity

46
Q

What is displacement

A

Includes both distance and object moves and the direction of that straight line
It’s a vector quantity

47
Q

What is the equation which links distance, speed, time

A

Speed(m/s) = Distance (m) / time(s)

48
Q

What is the typical speed of walking

A

1.5m/s

49
Q

What is the typical running speed

A

3m/s

50
Q

What is the typical cycling speed

A

6m/s

51
Q

What is the typical speed of sound in air

A

330m/s

52
Q

What is the typical speed of a car on main road

A

13m/s

53
Q

What is the typical speed of a fast train in UK

A

50m/s

54
Q

What is the typical speed of a cruising aeroplane

A

250m/s

55
Q

What is velocity

A

The velocity of an object is its speed in a given direction
It’s a vector quantity

56
Q

Explain how when a car moves in a circle it has a constant speed but changing velocity

A

Car is moving with a constant speed
Its direction is constantly changing
This means the velocity is constantly changing

57
Q

How can the speed be calculated from a distance-time graph

A

Gradient

58
Q

What does an upward sloping curve mean in a distance-time graph

A

The object is constantly increasing in speed (accelerating)

59
Q

What’s the equation for acceleration

A

Acceleration(m/s2) = change in velocity(m/s) / time(s)

60
Q

What is acceleration of an object

A

The change in velocity over a given time

61
Q

What is deceleration

A

An objects that slows down

62
Q

How is the acceleration calculated from a velocity-time graph

A

Gradient

63
Q

What is the equation for acceleration, final velocity, initial velocity, time

A

Acceleration = (final velocity-initial velocity)/ time

64
Q

What does the total area under a velocity-time graph tell us

A

The distance travelled in a specific direction (displacement)

65
Q

Explain the acceleration in an object falling through a fluid

A

It initially accelerates at 9.8m/s2 due to gravity
Eventually the resultant force will be zero
And the object will move at its terminal velocity

66
Q

What is Newton’s First law of motion

A

If the resultant force acting on a stationary object is zero, then the object will remain stationary.

If the resultant force acting on a moving object is zero, then the object will continue moving in the same direction at the same velocity.

67
Q

What is Newton’s Second law of motion

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

68
Q

What is the equation which links acceleration, force, mass

A

Force(N) = Mass (kg) X Acceleration(m/s2)

69
Q

Estimate the speed that cars travel on a main road and on a motorway

A

Main road - 13m/s
Motorway- 30m/s

70
Q

What is the typical acceleration to accelerate from a main road to a motorway

A

2m/s2

71
Q

What is the force needed for a family car to accelerate from a main road to a motorway

A

2000N

72
Q

What is inertial mass

A

The ratio of the force needed to accelerate an object over the acceleration produced.
It’s a measure of how difficult it is to change the velocity of an object
An object with a large inertial mass will require a larger force to produce a given acceleration than an object with a smaller inertial mass.

73
Q

What is Newton’s Third Law of motion

A

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

74
Q

Describe the forces acting on a skydiver

A

When the skydiver jumps off the plane the only force acting is weight due to gravity. This force does not change during the journey.
Because of weight the skydiver experiences a resultant force downwards so they accelerate downwards
As they fall the skydiver experiences friction with air molecules due to air resistance. Air resistance acts upwards
The weight is still greater than air resistance so they still accelerate downwards
As the skydiver’s velocity increases the air resistance also increases
Eventually the air resistance balances the weight
So there is no resultant force and velocity stays constant . The skydiver has reached terminal velocity.
At this point the skydiver open their parachute so the surface area increases causing air resistance to increase
So the air resistance is greater than the weight
So there is a resultant force acting upwards
This causes the skydiver to decelerate
Because velocity decreased the air resistance also decreases
At a point the air resistance will balance the weight so the resultant force is zero
So the velocity stays constant at a low terminal velocity

75
Q

What is stopping distance

A

The total distance travelled from when the driver first spots an obstruction to when the car stops

76
Q

What is the thinking distance

A

The distance travelled by the car during the driver’s reaction time

77
Q

What is the braking distance

A

The distance the car travels from when the driver applies the brakes to when the car stops.

78
Q

How does speed affect the stopping distance

A

The greater the speed of the vehicle, the greater the stopping distance

79
Q

What is the typical range of the reaction time

A

0.2 s - 0.9 s

80
Q

What factors affect thinking distance

A

Speed
Reaction time
Tiredness
Drugs
Alcohol

81
Q

What factors affect braking distance

A

Speed
How effective the brakes are
Quality of the tyres
Road surface-wet or icy conditions reduce friction between tyres and the road increasing braking distance

82
Q

Which objects have no momentum

A

Objects that are not moving

83
Q

What is the equation for momentum

A

Momentum(kg m/s) = mass(kg) X velocity(m/s)

84
Q

What’s the unit for momentum

A

Kilograms metre per second
kg m/s

85
Q

What is the conservation of momentum

A

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

86
Q

What’s the equation that links force, mass, change in velocity, change in time

A

Force (N) = (Mass(kg) x change in velocity (m/s))/ change in time(s)

87
Q

Explain how rapid changes in momentum can be fatal

A

Rapid changes in momentum lead to huge forces applying and these are extremely dangerous
We can reduce the danger if we make the change in momentum happen over a longer period of time.

88
Q

What are 5 safety devices that slow down momentum change

A

Airbags
Seatbelts
Crashmat
Bike helmet
Cushioned surface
These reduce the forces acting and reduce the risk of serious injury

89
Q

Explain how a safety device reduces the risk of injury eg: seatbelt

A

Increase impact time
Decrease the rate of momentum
This decreases impact force

Physics (7 decks)

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