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Physics GCSE > Topic 2 - Motion and forces > Flashcards

Topic 2 - Motion and forces Flashcards

1
Q

What is a scalar quantity?

A

A quantity that has magnitude but no specific direction

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2
Q

What is a vector quantity?

A

A quantity that has both magnitude and a specific direction

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3
Q

What is the difference between scalar and vector quantities?

A

Vector quantities have specific directions; scalar quantities do not

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4
Q

Recall 6 vector quantities

A

1) Force
2) Velocity
3) Displacement
4) Weight
5) Acceleration
6) Momentum

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5
Q

Recall 6 scalar quantities

A

1) Speed
2) Distance
3) Mass
4) Energy
5) Temperature
6) Time

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6
Q

What is velocity?

A

Speed in a stated direction

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7
Q

speed = ?

A

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

s = d/t

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8
Q

distance travelled = ?

A

distance travelled (m) average speed (m/s) * time (s)

d = st

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9
Q

What does a diagonal, straight line on a distance/time graph show?

A

Constant speed

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10
Q

What does remaining stationary look like on a distance-time graph?

A

A horizontal, straight line

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11
Q

What does a horizontal, straight line on a distance/time graph show?

A

Remaining stationary

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12
Q

What does a curve that is becoming steeper on a distance/time graph show?

A

Acceleration

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13
Q

What does a curve that is becoming less steep on a distance/time graph show?

A

Deceleration

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14
Q

What does the gradient of a distance/time graph show?

A

Average speed

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15
Q

acceleration = ?

A

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

a = v-u/t

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16
Q

(final velocity)^2 - (initial velocity)^2 = ?

A

(final velocity (m/s))^2 - (initial velocity (m/s))^2 = 2 * acceleration (m/s) * distance (m)

v^2-u^2 = 2ax

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17
Q

What does an upward diagonal, straight line (/) on a velocity/time graph show?

A

Constant acceleration

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18
Q

What does a horizontal, straight line on a velocity/time graph show?

A

Constant speed

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19
Q

What does a curve that is becoming steeper on a velocity/time graph show?

A

Increasing acceleration

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20
Q

What does a curve that is becoming less steep on a velocity/time graph show?

A

Decreasing acceleration

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21
Q

What does a downward diagonal, straight line () on a velocity/time graph show?

A

Constant deceleration

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22
Q

What does the gradient of a velocity/time graph show?

A

Average acceleration

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23
Q

How can you determine distance travelled from a velocity/time graph?

A

Using the area between the graph line and the time axis (the area under the graph)

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24
Q

Describe step-by-step how to set up the light gate experiment and how the light gates can be used to determine acceleration

A

(tinyurl. com/lightgates)
1) Measure the mass of the trolley, the unit masses and the hanging hook. Also measure the length of the piece of card which will interrupt the light gate beams.
2) Set up the apparatus: place the trolley, with the card on top, on a ramp; place two light gates (connected to a data logger) above different points on the ramp; connect the trolley to a string which attaches to a pulley connected to a hanging mass on a hook. (see link above for full configuration)
3) Mark a line on the ramp just before the first light gate to make sure the trolley travels at the same distance every time - the light gate will record the initial speed as it begins to move.
4) Hold the trolley still at the start line, and then let go of it so that it starts rolling down the slope.
5) Each light gate will record the time when the trolley passes through it and (by dividing the length of the card by the time taken to pass) the speed of the trolley.
6) Use a=(v-u)/t to find the acceleration (t is the time taken to travel between the two light gates).

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25
Q

How can the light gate set up be used to investigate the relationship between inertial mass and acceleration when force is constant and what would you expect to be the results

A

(tinyurl.com/lightgates)

Add masses one at a time to the trolley - this will show that increasing inertial mass leads to decreasing acceleration as mass and acceleration are inversely proportional

26
Q

How can the light gate set up be used to investigate the relationship between force and acceleration when force is constant and what would you expect to be the results

A

(tinyurl.com/lightgates)

Start with all the masses loaded onto the trolley and transfer the masses (to keep the mass of the whole system the same) of the hook one at a time - this will show that increasing accelerating force leads to increasing acceleration as force and acceleration are proportional.

27
Q

What is normal wind speed?

A

5-20 m/s

28
Q

What is the approximate speed of sound (in air)?

A

340 m/s

29
Q

What is normal walking speed?

A

1.4 m/s

30
Q

What is normal cycling speed?

A

5.5 m/s

31
Q

What is normal running speed?

A

3 m/s

32
Q

What is normal car speed in a built-up area?

A

13 m/s

33
Q

What is normal car speed on a motorway?

A

31 m/s

34
Q

What is normal train speed?

A

Up to 55 m/s

35
Q

What is acceleration (g) in free fall?

A

10 m/s^2

36
Q

What is Newton’s first law?

A

An object will remain stationary or at a constant speed unless being acted upon by unbalanced forces

37
Q

What is Newton’s second law?

A

resultant force (N) = inertial mass (kg) * acceleration (m/s^2)

F = ma

38
Q

weight = ?

A

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

W = mg

39
Q

How is weight measured?

A

Using a calibrated spring balance AKA newton meter

40
Q

What is the relationship between the weight of a body and the gravitational field strength?

A

They are proportional to each other - if one increases, so does the other

41
Q

Why does an object that is moving in a circular orbit at a constant speed have a changing velocity?

A

Velocity is both the speed and direction of an object. An object travelling in a circle is constantly changing direction and so is constantly changing velocity.

42
Q

Why must there be a centripetal force for motion in a circle?

A

Since an object travelling in a circle is changing velocity, there must be a resultant force acting on it. The force acts towards the centre and is called a centripetal force.

43
Q

What does an object’s inertial mass measure?

A

How difficult it is to change the velocity of the object

44
Q

inertial mass = ?

A

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

m = F/a

45
Q

What is Newton’s third law?

A

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

46
Q

Describe the 2 pairs of forces due to Newton’s third law being exerted in a closed system of a book on a table on the floor

A

1) The book is pulled down by its weight due to gravity from Earth, and the book also pulls back up on Earth
2) The normal contact force from the table pushing up on the book, and the normal contact force from the book pushing down on the table

47
Q

Describe the pair of forces that keep the book staying still in equilibrium in a closed system of a book on a table on the floor

A

The book is pulled down by its weight due to gravity from Earth, and there is the normal contact force from the table pushing up on the book

48
Q

momentum = ?

A

momentum (kg m/s) = mass (kg) * velocity (m/s)

p = mv

49
Q

force = ? (in terms of momentum)

A

force (N) = change in momentum (kg m/s) / time (s)

F = (mv-mu)/t

50
Q

How does Newton’s third law explain conservation of momentum?

A

If a white ball hits a stationary red ball, the force exerted on the red ball will make it start moving and the reaction force from the red ball on the white ball will make the white ball slow down. The forces exerted will cancel each other out and so, as change in momentum = force * time and the force is equal to 0, the change in momentum will aslo be equal to 0 and so the total momentum will remain the same.

51
Q

If the momentum of a ball is equal to x and the momentum of another ball is equal to y and then they collide with each other, what will be the resultant sum of the balls’ momentums?

A

x + y (as it was before the collision) because momentum is always conserved

52
Q

What experiment can be used to measure human reaction times?

A

The ruler drop test:

Someone holds a ruler while the person being tested places their thumb and forefinger so that the ruler is hanging between them lined up with zero.

Without warning, the person holding the ruler lets go and the person being tested closes their thumb and finger to try to catch the ruler as quickly as possible.

The longer the distance the ruler travelled, the longer the reaction time of the participant.

53
Q

What is a typical reaction time in the ruler drop test?

A

0.2-0.6 s

54
Q

What is the typical reaction time of an alert driver?

A

1 s

55
Q

stopping distance = ?

A

stopping distance = thinking distance + braking distance

56
Q

What 5 factors affect reaction time?

A

1) Age
2) Tiredness
3) Sobriety
4) Distractions
5) Drugs

57
Q

What 6 factors affect stopping distance?

A

1) Mass of the vehicle
2) Speed of the vehicle
3) Driver’s reaction time
4) State of the vehicle’s brakes
5) State of the road
6) Amount of friction between the tyres and the road surface

58
Q

Why are large decelerations dangerous?

A

A rapid change in acceleration means a large force exerted on the car and the person in it which can cause damage

59
Q

What is the typical stopping distance for a road vehicle travelling at 30 mph?

A

23 m

60
Q

What is the typical stopping distance for a road vehicle travelling at 50 mph?

A

53 m

61
Q

What is the typical stopping distance for a road vehicle travelling at 70 mph?

A

96 m

62
Q

What is the relationship between braking distance and initial velocity? Why is this?

A

A squared relationship - if velocity increases by a factor of x, braking distance does by a factor of x^2. This is shown by the equation:

energy in the car’s kinetic energy store = work done by the brackets
or
1/2 * mass of the car (kg) * (speed of car (m/s))^2 = braking force (N) * braking distance (m)
or
1/2mv^2 = Fd

  • mass and braking force remain constant and therefore v^2 = constant*d.

Physics GCSE (4 decks)

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