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11BT > 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 some examples of contact forces

A

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

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6
Q

State some examples of non contact forces

A

Gravity, magnetism, electrostatic

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7
Q

State the equation with all units for Weight

A

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

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8
Q

What is the mathematical relationship between weight and mass.

A

They are directly proportional

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9
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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10
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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11
Q

When is work done?

A

When a force causes an object to move through a distance

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12
Q

What is the relationship between work done and energy transferred

A

Work done = energy transferred

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13
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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14
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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15
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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16
Q

State Hookes law equation with all units

A

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

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17
Q

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

A

Elastic potential energy.

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18
Q

Define elastic deformation

A

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

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19
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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20
Q

Define a moment

A

The turning effect of a force

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21
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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22
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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23
Q

Define a liquid

A

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

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24
Q

State the equation for pressure with all units

A

pressure = force / area
Pressure - Pa
Force - N
Area - m2

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25
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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26
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). This creates a resultant force upwards. This force is called the upthrust.

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27
Q

Define the atmosphere

A

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

28
Q

State the relationship between altitude and the density of the atmosphere

A

he atmosphere gets less dense with increasing altitude.

29
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 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. So atmospheric pressure decreases with an increase in height.

30
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.

31
Q

State the difference between speed and velocity

A

Speed is a scalar

Velocity is a vector

32
Q 
State the following typical speeds:
walking
Running
Cycling
Sound
A

walking - 1.5 m/s
Running - 3.0 m/s
Cycling - 6.0 m/s
Sound - 330 m/s

33
Q

State the equation with all units to calculate speed

A

distance (m) = speed (m/s) × time (s)

34
Q

how can speed be calculated from a distance - time graph

A

Using the gradient

35
Q

State the equation to calculate average acceleration, with all units

A

acceleration = change in velocity / time

acceleration - m/s2
velocity - m/s
time - s

36
Q

How can acceleration be found from a velocity - time graph

A

From the gradient

37
Q

How can displacement be found from a velocity - time graph

A

From the area under the line

38
Q

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

A

9.8 m/s2

39
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

40
Q

What factors can increase the size of air resistance

A

Speed
Surface area
Density of the fluid which the object is falling through

41
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

42
Q

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

A

Inertia

43
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.

44
Q

State the equation with all units for Newtons Second law

A

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

45
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.

46
Q

State Newton’s third law

A

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

47
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).

48
Q

Define thinking distance

A

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

49
Q

Define braking distance

A

the distance the car travels whilst the brakes are applied

50
Q

State the typical reaction times for a human

A

0.2 s to 0.9 s.

51
Q

State some factors that can affect a persons reaction times

A

tiredness, ages, drugs and alcohol, Distractions

52
Q

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

A

Rain, ice, snow, poor quality brakes, poor quality tyres, gradient of the road, mass of the car

53
Q

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

A

Speed

54
Q

State the equation for momentum

A

momentum = mass × velocity

55
Q

State the units for momentum

A

kg m/s

56
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.

57
Q

What is required to change the momentum of an object

A

A force

58
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

A 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

59
Q

Define acceleration

A

when an object speeds up, slows down or changes direction.

60
Q

Units of force

A

Newtons (N)

61
Q

What is the centre of mass of an object?

A

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

62
Q

Where does the centre of mass lie in symmetrical objects?

A

Along the line of symmetry

63
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

64
Q

What is a gear?

A

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

65
Q

What do gears act as?

A

A force multiplier

66
Q

What are the dangers of a large braking force?

A

Brakes overheating, loss of control and skidding

67
Q

Define inertia

A

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

11BT (18 decks)

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