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Physics > CP2 > Flashcards

CP2 Flashcards

1
Q

What type of quantities are all forces?

A

Vector quantities.

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2
Q

What is a resultant force?

A

The total force that results from two or more forces acting upon a single object.

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3
Q

How do you work out resultant force?

A
  1. If the forces are acting in the same direction, add them
  2. If they are acting in opposite directions, subtract one from the other
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4
Q

When are forces balanced?

A

When the resultant of all the forces on an object is zero.

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5
Q

When are forces unbalanced?

A

When the resultant of the forces is not zero.

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6
Q

What is Newton’s first law of motion?

A
  1. An object in motion will remain in motion at the same speed and direction unless an external force acts on it.
  2. An object at rest and will not move unless an external force acts on it.
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7
Q

How will balanced forces affect the velocity of an object?

A

They will not change the velocity of an object.

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8
Q

How will unbalanced forces affect the velocity of an object?

A

They will change the speed and direction (the velocity) of an object.

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9
Q

What happens to the velocity of an object when moving in a circular path?

A

The velocity still changes and the object accelerates when moving in a circular path.

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10
Q

What are centripetal forces?

A

A force that causes an object to follow a circular path.

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11
Q

What direction do centripetal forces act towards?

A

The force acts towards the centre of a circle.

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12
Q

What forces can make an object move in a circular path (what forces are centripetal forces)?

A
  1. Friction
  2. Tension
  3. Gravity
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13
Q

Why does the velocity of an object change despite the speed staying the same when travelling in a circular path?

A

As the object is always changing direction when travelling in a circular path, meaning the velocity must also change.

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14
Q

What is mass?

A

A measure of how much matter there is in an object, and it only changes if the object itself changes.

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15
Q

What is weight?

A

A measure of the pull of gravity on an object and it depends on the strength of gravity.

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16
Q

What is mass measured in (unit)?

A

Kilograms (KG).

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17
Q

How can weight be measured?

A

By using a force meter, which has a scale in Newtons.

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18
Q

What is a force meter?

A

A meter, often containing a spring, which measures forces in newtons.

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19
Q

What is the value of gravitational field strength on Earth?

A

10 Newtons per kilogram (10N/Kg).

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20
Q

What is weight measured in (unit)?

A

Newtons (N).

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21
Q

What is gravitational field strength and what is it usually measured in?

A

A measure of how strong the force of gravity is somewhere. It is usually measured in N/KG.

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22
Q

What is the equation for the weight of an object?

A

Weight (N)=Mass(Kg)xGravitational field strength(N/kg)

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23
Q

What is the formula triangle for weight, mass and gravitational potential energy?

A

Weight
Mass | GPE

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24
Q

What is the difference between mass and weight?

A

Mass is the amount of matter in an object while Weight is the pull of gravity on an object.

25
Q

How does the velocity of a skydiver change as they fall?

A

0.5s after jumping (5m/s speed): Air resistance increases with speed, so just after jumping the air resistance is much smaller than her weight. The large resultant force makes her accelerate downwards.
3s after jumping (25m/s speed): Her air resistance is larger but her weight stays the same. The resultant force is smaller, so she is still accelerating, but not as much.
12s after jumping (55m/s speed): She is moving so fast that the air resistance balances her weight. She continues to fall at the same speed.

26
Q

What is Newton’s second law of motion?

A

The acceleration in the direction of a resultant force depends on:
1. The size of the force (for the same mass, the bigger the force the bigger the acceleration)
2. The mass of the object (for the same force, the more massive the object the slower the acceleration)

27
Q

What is the equation for force of an object?

A

Force (N)=Mass(Kg)xAcceleration(m/sˆ2)

28
Q

What are the units for the force equation?

A

f=mxa (f=force, m=mass, a=acceleration)

29
Q

What are the units for the weight equation?

A

w=mxg (w=weight, m=mass, g=gravitational potential energy)

30
Q

What is inertial mass?

A

The force on an object divided by the acceleration the force produces

31
Q

How do you calculate inertial mass?

A

Inertial mass=force/acceleration (m=f/a)

32
Q

What is the formula triangle for force, mass and acceleration?

A

Force
Mass | Acceleration

33
Q

How does the size of an object affect the amount of force needed to change velocity?

A

The more massive an object is, the more force is needed to change its velocity (either to make it start moving or to change the velocity of a moving object)

34
Q

What experiment can demonstrate Newtons second law of motion?

A

The trolley mass experiment (putting a trolley down a ramp and measuring its speed and repeating the experiment by changing the mass and seeing the change in results)

35
Q

What is Newton’s third law of motion?

A

It is about the forces on two objects when they interact with each other. This interaction can happen:
1. When objects touch, such as when you sit on a chair
2. At a distance, such as the gravitational attraction between the earth and the moon

36
Q

What are action-reaction forces and what are some of their characteristics?

A

Pairs of forces on interacting objects that are always the same size, in opposite directions, and acting on different objects.

37
Q

What is the difference between action-reaction forces and balanced forces?

A

Action-reaction forces act on different objects whereas balanced forces act on the same object only.

38
Q

What is an equilibrium situation?

A

When all forces are balanced.

39
Q

What happens to action-reaction forces during a collision?

A

The action and reaction forces are both the same size, but they do not necessarily have the same effects on the two objects, because the objects have different masses.

40
Q

What is momentum?

A

A measure of the tendency of an object to keep moving - or of how hard it is to stop it moving.

41
Q

What does the momentum of an object depend on?

A

It depends on an objects mass and velocity.

42
Q

What type of quantity is momentum?

A

A vector.

43
Q

What is the equation for momentum of an object?

A

momentum(kgm/s)=mass(kg)xVelocity(m/s)

44
Q

What are the units for the weight equation?

A

p=mxv (p=momentum, m=mass, v=velocity)

45
Q

What is the formula triangle for momentum, mass and velocity?

A

Momentum
Mass | Velocity

46
Q

What is conservation of momentum?

A

The total momentum of moving objects before a collision is the same as the total momentum afterwards as long as no external forces are acting.

47
Q

What happens to momentum once a collision between objects of the same mass occurs?

A

They split the momentum between them (an object with 6m/s bumps into an object with 0m/s= 3m/s for both objects afterwards as momentum is shared)

48
Q

What is thinking distance?

A

The distance travelled by a vehicle while a driver reacts.

49
Q

What is braking distance?

A

The distance travelled by a vehicle while the brakes are working to bring it to a halt.

50
Q

What is stopping distance?

A

Stopping distance=Thinking distance + Braking distance

51
Q

How can you measure human reaction time?

A
  1. Computers
  2. Electric circuits that measure the time between a stimulus and a response
52
Q

What is the typical human reaction time?

A

0.25 seconds.

53
Q

What factors can affect reaction time (make it worse) and thinking distance?

A
  1. Tiredness
  2. Illness
  3. Consumption of drugs
  4. Consumption of alcohol
  5. Distractions (such as phones)
54
Q

What factors can affect braking distance?

A
  1. Weather
  2. Condition of the road
  3. Condition of the tires/brakes
  4. Speed
  5. Mass of vehicle
55
Q

What does the force needed for acceleration/deceleration depend on?

A

It depends on the size of the acceleration/deceleration needed and the mass of the object.

56
Q

What is a crumple zone?

A

A vehicle safety device in which part of the vehicle is designed to crumple in a crash, reducing the force on impact.

57
Q

What are some safety features that modern cars have?

A
  1. Crumple zones
  2. Seat belts
  3. Airbags
58
Q

How can you calculate force by combining two equations together?

A

Force=change in momentum/time

58
Q

What are the units for the weight equation?

A

F=mv-mu/t (f=force, mv-mu=change in momentum, t=time)

Physics (13 decks)

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