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y physics paper two > forces > Flashcards

forces Flashcards

1
Q

What is a scalar quantity? Give some examples.

A

A scalar quantity has magnitude but no direction. Examples are speed, distance, mass and temperature.

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2
Q

What is a vector quantity? Give some examples.

A

A vector quantity has magnitude and direction. Examples are force, velocity, displacement and acceleration. They can be represented by an arrow, with the length as magnitude and direction as direction.

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3
Q

What is a force? What are the two types of forces?

A

A force is a push or pull that acts on an object due to the interaction with another object. All forces are either contact (the objects are physically touching) or non-contact (the objects are physically separated).

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4
Q

Give three examples of contact forces.

A

Contact forces are friction, air resistance and tension.

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5
Q

Give three examples of non-contact forces.

A

Non-contact forces are gravitational, electrostatic and magnetic.

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6
Q

What is an interaction pair of forces?

A

An interaction pair of forces are equal and opposite, and act on two interacting objects. For example, a chair exerts a force on the ground, whilst the ground pushes back with the same push.

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7
Q

What is weight? How can this force be made stronger?

A

Weight is the force acting upon an object due to gravity, measured in Newtons, N. This is due to the gravitational field around the Earth. It is stronger closer to the mass causing the field and stronger for larger masses.

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8
Q

What is the centre of mass of an object?

A

The centre of mass of an object is where the whole mass is concentrated. It is where we believe the force (of weight) is acting upon. For a uniform object (constant density) of a regular shape, the centre of mass is the centre of the object.

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9
Q

How is weight measured?

A

Weight is measured with either a calibrated spring balance or a newtonmetre.

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10
Q

How is weight calculated?

A

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

- weight and mass are directly proportional

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11
Q

What is a resultant force?

A

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

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12
Q

What are the forces acting on an object with constant velocity?

A

If an object has a constant velocity, then there is an equal air resistance and thrust.

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13
Q

What are the forces acting on an object with constant altitude?

A

If an object has a constant altitude, then there is equal lift and weight.

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14
Q

What does 1cm represent in a vector diagram?

A

In a vector diagram, 1cm = 10N

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15
Q

What does it mean if an object is at equilibrium?

A

If an object is at equilibrium, the forces acting on it are balanced.

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16
Q

What does work done mean?

A

When a force moves an object a distance, work is done on the object. Energy is transferred when this is done. Work done against frictional forces acting on an object causes a rise in temperature of the object.

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17
Q

How is work done calculated?

A

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

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18
Q

What three things could two forces cause an object to do?

A

Applying a force to an object may cause it to compress, stretch or bend. Two forces must be acting on it or else it’ll just move. It causes the energy to be transferred to the elastic potential energy store.

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19
Q

What is elastic deformation?

A

Elastic deformation can return to its original shape or length. Only elastic objects can do this.

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20
Q

What is inelastic deformation?

A

Inelastic deformation cannot return to its original shape and length.

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21
Q

How is force calculated? (in terms of elasticity)

A

force (N) = spring constant (N/m) x extension/compression (m)
- spring constant is always given in the exam

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22
Q

What is the relationship between the work done and elastic potential energy of a spring?

A

The work done on the spring and the elastic potential energy stored are equal, provided the spring isn’t elastically deformed.

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23
Q

What is a moment?

A

A force or a system of forces may cause an object to rotate. The turning effect of a force is called the moment. To turn, it needs a pivot.

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24
Q

How is a moment calculated?

A

moment (Nm) = force (N) x distance (m)

- the distance is the perpendicular distance from the pivot to the line of action

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25
Q

What does it mean if an object is balanced?

A

An object is balanced when the total clockwise movement about a pivot is equal to the anticlockwise movement about that pivot.

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26
Q

What is a simple lever or gear system be used for?

A

A simple lever or gear system is used to transmit the effects of the rotational effects of forces.

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27
Q

What do levers do?

A

Levers increase the distance from the pivot at which the force is applied, so less force is needed for the same moment.

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28
Q

What are gears? What do they do?

A

Gears are circular discs with ‘teeth’ around the edges. Their teeth interlock so turning one causes another to turn in the opposite direction. Different sized gears can change the moment, like a larger gear means the moment is larger as the distance is greater, so it will turn slower.

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29
Q

What are fluids?

A

Fluids can either be a liquid or a gas; the particles have to flow.

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30
Q

Describe how the pressure in fluids is exerted.

A

The pressure in fluids cause a force normal (at right angles) to any surface.

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31
Q

How do you calculate pressure at the surface of a fluid?

A

pressure (Pa) = force (N) / area (m^3)

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32
Q

Why does the pressure of a liquid increase with depth?

A

The pressure of a liquid increases with depth as the number of particles above that point increases, so the weight of those particles is felt, increasing the pressure.

33
Q

Describe how upthrust occurs.

A

A partially or totally submerged object experiences a greater pressure on the bottom of the surface than the top surface, which creates a resultant force upwards, called upthrust. The size of upthrust is equal to the weight of water displaced.

34
Q

Why do less dense objects float?

A

Objects that are less dense than water only have to displace a small volume of water before it equals its weight (smaller than the object itself). Then, the size of upthrust and weight equal and the object floats above water.

35
Q

Why do more dense objects sink?

A

Objects which are more dense than water can’t displace a volume of water equal to its own weight, so the size of weight is greater than upthrust, so the object sinks.

36
Q

How is atmospheric pressure created?

A

Atmospheric pressure is created by air molecules colliding with the surface.

37
Q

How is atmospheric pressure altered with height?

A

The number of air molecules (and so the weight of the 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 then there is at a lower height, so atmospheric pressure decreases as height increases.

38
Q

What is distance?

A

Distance is how far an object moves and does not involve direction, so it is scalar.

39
Q

What is displacement?

A

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

40
Q

What is the typical speed of walking?

A

walking - 1.5m/s

41
Q

What is the typical speed of running?

A

running - 3m/s

42
Q

What is the typical speed of cycling?

A

cycling - 6m/s

43
Q

What is the typical speed of a car?

A

car - 25m/s

44
Q

What is the typical speed of a train?

A

train - 55m/s

45
Q

What is the typical speed of a plane?

A

plane - 250m/s

46
Q

What is the speed of sound in air?

A

speed of sound in air - 330m/s

47
Q

How do you calculate speed?

A

speed (m/s) = distance (m) / time (s)

48
Q

What is velocity?

A

Velocity is speed in a given direction. It is a vector.
eg. an object moving in a circle at a constant speed has a constantly changing velocity as the direction is always changing

49
Q

How do you calculate speed on a distance time graph?

A

The gradient of a distance time graph is the speed. (if accelerating, use a tangent)

50
Q

What is acceleration?

A

Acceleration is the change in velocity in a certain amount of time. It is a vector. Uniform acceleration is constant acceleration.

51
Q

How do you calculate acceleration?

A

acceleration (m/s^2) = change in velocity (m/s) - time (s)

52
Q

What is any object’s acceleration falling freely under gravity near the Earth’s surface?

A

Near the Earth’s surface, any object falling freely under gravity has an acceleration of about 9.8m/s^2.

53
Q

Describe how terminal velocity is reached through a fluid.

A

An object 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, or its maximum speed, as the frictional force is equal to the accelerating force.

54
Q

How do you calculate acceleration on a velocity time graph?

A

The gradient of a velocity time graph is the acceleration.

55
Q

How do you calculate distance traveled on a velocity time graph?

A

The area under a velocity time graph is the distance traveled.

56
Q

What is drag?

A

Drag is the friction that acts in the opposite direction to movement. This force increases as speed increases.

57
Q

When does friction occur?

A

Friction occurs when two surfaces are in contact or when an object passes through a fluid.

58
Q

For an object to travel at a steady speed, what must happen to the forces acting on it?

A

To travel at a steady speed, the driving force needs to be equal to the frictional force.

59
Q

What is Newton’s First Law?

A

Newton’s First Law:

  • if the resultant force on a stationary object is zero then the object is stationary or moving at a constant speed in the same direction (so same velocity)
  • therefore, velocity will only change if there is a resultant force
60
Q

What is inertia?

A

Inertia is the tendency of objects to continue in their state of rest or motion.

61
Q

What is Newton’s Second Law?

A

Newton’s Second Law:
- the acceleration of an object is proportional to the resultant force on an object, and inversely proportional to the mass of the object

62
Q

What is the equation that links to Newton’s Second Law?

A

force (N) = mass (kg) x acceleration (m/s^2)

63
Q

What is inertial mass?

A

Inertial mass is a measure of how difficult it is to change the velocity of an object. A larger inertial mass requires a larger force to produce a given acceleration.

64
Q

What is Newton’s Third Law?

A

Newton’s Third Law:

  • whenever two objects interact, the forces they exert on each other are equal and opposite
  • eg. when two skaters push off each other, they are moved away from each other by the same force that they push with
65
Q

What is thinking distance?

A

Thinking distance is the distance traveled between the driver seeing the hazard and applying the brake.

66
Q

What is braking distance?

A

Braking distance is the distance between when the brakes are applied and when the vehicle stops.

67
Q

What is stopping distance?

A

Stopping distance is the distance from when the driver sees the hazard to when the car stops.
stopping distance = thinking distance + braking distance

68
Q

What factors affect thinking distance?

A

Thinking distance is affected by speed and reaction time.

69
Q

What factors affect braking distance?

A

Braking distance is affected by speed, weather, road surface, condition of the tires and brakes.

70
Q

How might large decelerations lead to overheating brakes or loss of control?

A

When a force is applied to the brakes, work is done by the friction force between the brakes and the wheel, which reduces the kinetic energy of the vehicle and the temperature of the brakes increase due to friction. The greater the speed, the greater force needed to brake in a given distance, which means a higher frictional force, so more overheating.

71
Q

What is the typical range of reaction times?

A

0.2-0.9s

72
Q

What four factors may affect reaction time?

A

factors affecting reaction time:

  • distractions
  • drugs
  • tiredness
  • alcohol
73
Q

What is momentum?

A

Momentum is about the quantity of motion of an object, so the ‘oomph’ of it. It is a vector quantity.

74
Q

How do you calculate momentum?

A

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

75
Q

What is the conservation of momentum?

A

conservation of momentum:
- in a closed system (no external forces acting), the total momentum before an event is equal to the total momentum after the event

76
Q

What is required for a change in momentum?

A

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

77
Q

Why are rapid changes in momentum dangerous?

A

Rapid changes in momentum can be dangerous as they lead to huge forces applied to one person. eg. if a car crashes
The higher the force, the higher the change in momentum.
The more time taken to stop, the lower the force, and so the lower the change in momentum.

78
Q

What four things can slow down the change in momentum?

A

slowing change in momentum:

  • air bags - compressing the air slows the speed
  • crash mats - longer time needed to fall to the ground due to compression of air
  • seat belts - stretch, which decreases how fast you move
  • bike helmets - crushable layer lengthens time for head to stop
79
Q

Why do objects that are the same density as water float?

A

Objects that are the same density as water displace a volume of water equal to the object as the weight of this will equal the weight of the object. After this, the size of upthrust and weight equal, and the object floats, just on the surface of the water.

y physics paper two (5 decks)

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