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11AT > Forces - paper 2 > Flashcards

Forces - paper 2 Flashcards

To revise forces (Paper 2)

1
Q

Define a scalar

A

A quantity that only has magnitude.

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2
Q

Give some examples of scalar quantities

A

Speed, distance, time, mass, volume

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3
Q

Define a vector quantity

A

A quantity that has magnitude and direction.

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4
Q

Give some examples of vector quantities

A

Velocity, displacement, acceleration, momentum, any force

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5
Q

State the difference between distance and displacement

A

Distance is a scalar - doesn’t involve direction

Displacement is a vector and is measured in a straight line from the start point to the finish point and the direction of that straight line.

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6
Q

State the difference between speed and velocity

A

Speed is a scalar - only has magniture

Velocity is a vector - has magniture and direction

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7
Q

State some examples of contact forces

A

Friction, air resistance, drag, upthrust, tension, normal contact force

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8
Q

State some examples of non contact forces

A

Gravity, magnetism, electrostatic attraction or repulsion

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9
Q

State the equation with all units for Weight

A

weight (N) = mass (kg) × gravitational field strength(N/kg)

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10
Q

What is the mathematical relationship between weight and mass.

A

They are directly proportional, if mass doubles then does weight

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11
Q

What equipment can be used to measure weight?

A

Weight is measured using a calibrated spring-balance called a newtonmeter

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12
Q

Define a resultant force

A

When 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.

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13
Q

Units of force

A

Newtons (N)

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14
Q

When is work done?

A

When a force causes an object to move through a distance

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15
Q

What is the relationship between work done and energy transferred

A

Work done = energy transferred

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16
Q

State the equation and all units for work done

A

work done (J) = force (N) × distance moved along the line of action of the force (m)

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17
Q

Define 1 joule of work

A

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

1 joule = 1 newton-metre

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18
Q

State Hooke’s law

A

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.

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19
Q

State Hookes law equation with all units

A

force (N) = spring constant (N/m) × extension (m)

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20
Q

When an object is stretched or squared what form of energy does it store?

A

Elastic potential energy.

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21
Q

Define elastic deformation

A

When the forces are removed the object returns to its original length

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22
Q

Define inelastic deformation

A

When the forces are removed the object doesn’t returns to its original length, it stays permanently stretched.

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23
Q

Define a moment

A

The turning effect of a force

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24
Q

State the equation for a moment, with all units

A

moment of a force (Nm) = force (N) × perpendicular distance (m)

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25
Q

If an object is balanced what can you say about the clockwise and anticlockwise moments

A

They must be equal

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26
Q

Define a fluid

A

Either a liquid or gas, particles must be able to move past each other

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27
Q

State the equation for pressure with all units

A

pressure = force / area

Pressure - Pa

Force - N

Area - m2

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28
Q

What is the relationship between pressure from a liquid and depth

A

As depth increases pressure increase due to a greater number of particles and force pushing on the object.

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29
Q

How does liquid pressure cause upthrust?

A

A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface, (pressure increases with depth).

Force = Pressure x area so there is a greater force on the bottom surface than the top.

This creates a resultant force upwards. This force is called the upthrust.

30
Q

Define the atmosphere

A

The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth.

31
Q

State the relationship between altitude and the density of the atmosphere

A

he atmosphere gets less dense with increasing altitude.

32
Q

As altitude increase why does atmospheric pressure decrease?

A

Air molecules colliding with a surface create atmospheric pressure. The number of air molecules (and so the weight of air) above a surface decreases as the height above ground level increases. So as height increases there is always less air above a surface than there is at a lower height. So atmospheric pressure decreases with an increase in height.

33
Q
A
34
Q

State the equation with all units to calculate speed

A

distance (m) = speed (m/s) × time (s)

35
Q

how can speed be calculated from a distance - time graph

A

Using the gradient

36
Q

State the equation to calculate average acceleration, with all units

A

acceleration = change in velocity / time

a = (v-u) / t

acceleration - m/s2

velocity - m/s

time - s

37
Q

Define acceleration

A

Rate of change of velocity. An acceleration can be when an object:

  1. speeds up
  2. slows down
  3. changes direction
38
Q

How can acceleration be found from a velocity - time graph

A

From the gradient

39
Q

How can displacement be found from a velocity - time graph

A

From the area under the line

40
Q

What is the initial rate of acceleration for an object falling close to the earths surface?

A

9.8 m/s2

41
Q

What is terminal velocity and when does it occur?

A

the maximum velocity an object can fall at, this happens when forces are balanced (Weight = air resistance)

42
Q

What factors can increase the size of air resistance

A
  1. Speed
  2. Surface area
  3. Density of the fluid which the object is falling through
43
Q

State Newtons first law

A

if the resultant force acting on an object is zero the object will stay at rest or move at a constant velocity

44
Q

The tendency of objects to continue in their state of rest or of uniform motion is called?

A

Inertia

45
Q

State Newtons 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.

a = F/m

46
Q

State the equation with all units for Newtons Second law

A

resultant force (N) = mass (kg) × acceleration (m/s2)

47
Q

Define inertial mass

A

Inertial mass is a measure of how difficult it is to change the velocity of an object.

Inertial mass is defined as the ratio of force over acceleration.

m = F/a

48
Q

Define inertia

A

the tendency of an object to continue in its state of rest or motion

49
Q

State Newton’s third law

A

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

50
Q

Define stopping distance

A

The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).

Stopping distance = thinking distance + braking distance

51
Q

Define thinking distance

A

the distance the car travels whilst a driver reacts to a situation

52
Q

Define braking distance

A

the distance the car travels whilst the brakes are applied

53
Q

State the typical reaction times for a human

A

0.2 s to 0.9 s.

54
Q

State some factors that can affect a persons reaction times

A
  1. tiredness,
  2. ages,
  3. drugs and alcohol,
  4. Distractions
55
Q

State some factors that can affect the braking distance of a car

A
  1. Rain,
  2. ice,
  3. snow,
  4. poor quality brakes,
  5. poor quality tyres,
  6. gradient of the road,
  7. mass of the car
56
Q

State the one factor that can increase both the thinking distance and braking distance

A

Speed

57
Q

State the equation for momentum

A

momentum (kgm/s) = mass (kg) × velocity (m/s)

58
Q

State the units for momentum

A

kg m/s

59
Q

Define the conservation of momentum

A

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

Provided no external force is applied

60
Q

What is required to change the momentum of an object

A

A force

61
Q

Explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds with reference to the concept of rate of change of momentum.

A

An air bag increases the time** for a person to stop. Therefore for the **same change of momentum** a **smaller force can be used.

Force = change in momentum/time

62
Q

What is the centre of mass of an object?

A

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

63
Q

Where does the centre of mass lie in symmetrical objects?

A

Along the line of symmetry

64
Q

How can the centre of mass of an irregular shape be found?

A

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 Where the lines meet is the centre of mass

65
Q

What is a gear?

A

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

66
Q

What do gears act as?

A

A force multiplier

67
Q

What are the dangers of a large braking force?

A

Brakes overheating, loss of control and skidding

68
Q

State the typical walking speed of a person

A

1.5 m/s

69
Q

State the typical running speed of a person

A

3.0 m/s

70
Q

State the typical cycling speed of a person

A
71
Q

State the speed of sound

A

330 m/s

11AT (18 decks)

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