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Physics > 2. Motion and Forces > Flashcards

2. Motion and Forces Flashcards

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1
Q

What is a scalar quantity?

A
  • A quantity that only has a magnitude.
  • A quantity that isn’t direction dependent.
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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction.

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3
Q

How can a vector quantity be drawn?

A

Using vector arrows.

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4
Q

How do vector arrows represent vectors?

A
  • The length of the arrow represents the magnitude.
  • The arrow points in the associated direction.
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5
Q

Give examples of vector quantities

A
  • Velocity
  • Displacement
  • Force
  • Acceleration
  • Weight
  • Momentum
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6
Q

Give examples of scalar quantities

A
  • Temperature
  • Time
  • Mass
  • Speed
  • Distance
  • Energy
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7
Q

What is velocity?

A

The speed of an object in a specific direction.

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8
Q

Give an equation relating average speed, distance and time.

A

average speed = distance / time

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9
Q

On a distance/time graph, what value does the gradient of the line represent?

A

The speed.

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10
Q

On a displacement/time graph, what value does the gradient of the line represent?

A

The velocity.

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11
Q

What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?

A
  • Draw a tangent to the curve at the required time.
  • Calculate the gradient of the tangent.
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12
Q

How can the distance travelled by an object be calculated from a velocity-time graph

A

It is equal to the area under the graph.

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13
Q

On a velocity/time graph what does the gradient of the line represent?

A

The acceleration.

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14
Q

State a typical value for the speed of sound

A

340 m/s

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15
Q

What is a typical value for human walking speed?

A

1.4 m/s

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16
Q

What is a typical value for human running speed?

A

3 m/s

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17
Q

What is a typical value for human cycling speed?

A

6 m/s

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18
Q

Give an appropriate value for the acceleration of an object in free fall under gravity near the Earth’s surface.

A

10 m/s²

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19
Q

What is displacement?

A

A vector quantity which measures the distance and the direction in a straight line from an object’s starting point to its finishing point.

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20
Q

What is acceleration?

A

The change in velocity in a certain amount of time.

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21
Q

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

A

The resultant force.

22
Q

What is Newton’s First Law for a stationary object?

A

If the resultant force on a stationary object is zero, the object doesn’t move.

23
Q

What is Newton’s First Law for a moving object?

A

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).

24
Q

State the defining equation for Newton’s Second Law

A

Resultant force = mass x acceleration

F = ma

25
Q

What is Newton’s Second Law in words?

A

An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.

26
Q

What is weight?

A

The force that acts on an object due to gravity and the object’s mass.

27
Q

What quantities does weight depend on?

A

Weight = mass x gravitational field strength

  • The object’s mass
  • The gravitational field strength at the given position in the field.
28
Q

What is the unit used for weight?

A

Newton (N)

29
Q

What is the unit used for gravitational field strength?

A

N/kg

30
Q

What piece of equipment can be used to measure an object’s weight?

A

A calibrated spring-balance or newton-meter.

31
Q

When can an object travelling at a constant speed not have a constant velocity?

A

When the object is changing direction; for example, moving in a circle.

32
Q

Why does an object travelling at a constant speed in a circle not have a constant velocity?

A
  • Speed is a scalar quantity.
  • Velocity is a vector quantity which means it can only be constant if the direction is constant.
  • In circular motion, the direction is continuously changing.
  • Therefore velocity is constantly changing.
33
Q

What is the resultant force that acts on an object moving in a circle called, and in which direction does it act?

A

It is called the centripetal force and acts towards the centre of the circle.

34
Q

What is inertial mass?

A
  • A measure of how difficult it is to change a given object’s velocity.
  • The ratio of force over acceleration.
35
Q

State Newton’s Third Law

A

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

36
Q

State the equation used to calculate an object’s momentum.

A

Momentum = mass x velocity

37
Q

What is the unit used for momentum?

A

kgm/s

kilogram metres per second

38
Q

What is conservation of momentum?

A

In a closed system, the total momentum before and after are equal.

39
Q

How can you measure human reaction times?

A
  • Using the ruler drop test.
  • Person A and B hold each end of a ruler with the 0cm mark at the bottom.
  • Person A drops the ruler without telling Person B.
  • Person B catches it.
  • The distance travelled corresponds to their reaction time.
40
Q

In the ruler drop test, why is it important that the 0cm mark is at the bottom?

A

So you can obtain the distance directly without having to calculate it; otherwise, a zero error would need to be accounted for.

41
Q

What is the stopping distance of a vehicle equal to?

A

The sum of thinking distance and braking distance.

42
Q

For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?

A

The stopping distance is increased with an increase in speed.

43
Q

Give a typical range of values for human reaction time.

A

0.2 seconds - 0.9 seconds

44
Q

Give three factors which can affect a driver’s reaction time.

A
  • Tiredness
  • Drugs/alcohol
  • Distractions (such as noise)
45
Q

Factors which may increase braking distance.

A
  • Faster vehicle speed
  • Poor, wet, or icy road surface conditions
  • Damaged or worn brakes or tyres conditions.
46
Q

Factors which may increase thinking distance.

A
  • Faster vehicle speed
  • Long driver reaction times
47
Q

What is thinking distance?

A

How far a vehicle moves during driver’s reaction time.

48
Q

What is braking distance?

A

The distance taken to stop whilst brakes are applied.

49
Q

Describe the energy transfers that take place when a car applies its brakes.

A
  • Work is done by the friction force between the brakes and wheel.
  • Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs.
50
Q

To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?

A

The braking force must also be increased.

51
Q

State two consequences of a vehicle undergoing very large decelerations.

A
  • Kinetic energy converted to heat is very high causing brakes to overheat.
  • Loss of control of the vehicle, causing it to skid.

Physics (13 decks)

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