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N5 physics > Dynamics > Flashcards

Dynamics Flashcards

1
Q

What is a scalar

A

Scalars are quantities that are fully described by its magnitude.

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2
Q

Examples of scalar quantities

A

Time
Mass
Energy
Speed
Distance
Volume

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3
Q

What is a vector

A

Vectors are quantities that are described by both magnitude and direction.

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4
Q

Examples of vectors

A

Velocity
Displacement
Force
Acceleration
Momentum

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5
Q

What is displacement

A

a distance with a direction.

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6
Q

What is velocity

A

a speed with a direction

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7
Q

Displacement=

A

Average Velocity x Time

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8
Q

Average velocity=

A

Displacement/Time

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9
Q

Area of triangle=

A

1/2 base x height

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10
Q

Area of rectangle

A

base x height

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11
Q

On velocity-time graphs what is gradient

A

Acceleration

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12
Q

On velocity-time graphs what is area

A

displacement

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13
Q

What is acceleration

A

the change in velocity in a period of time

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14
Q

What is the equation of acceleration

A

a=(v-u)/t

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15
Q

Describe how to measure average speed

A

Mark a start line and finish line
Measure the distance between the start and finish line with a metre stick
Start a stopwatch when the object crosses the start line and stop it when it crosses the finish line
Calculate the average speed = distance between start and finish line / time on stopwatch

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16
Q

Describe how to measure average speed using the equipment with the car and ramp

A

Two light gates are connected to a timer
The car rolls down the slope
When the mask breaks the fist lightgate beam it starts the timer
When the mask breaks the the second lightgate beam it stops the timer
Measure the distance between the two lightgates using a metre stick
Calculate the speed = distance between lightgates / time on timer

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17
Q

Explain the difference between average and instantaneous speed

A

Average is over a long period of time. Instantaneous speed is the speed over a very short period of time (an instant)

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18
Q

What is the difference between a vector and a scalar quantity?

A

A scalar needs size/magnitude to be described correctly. A vector quantity needs size/magnitude and direction to be described correctly.

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19
Q

What is the difference between distance and displacement?

A

Distance is the length of the path you actually take and is a scalar. Displacement is the straight line distance between the start point and finish point and includes a direction as it is a vector.

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20
Q

What is the difference between speed and velocity?

A

Speed is a scalar and is equal to distance divided by time. Velocity is a vector and is displacement divided by time, with a direction.

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21
Q

What is speed?

A

Distance travelled per second

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22
Q

What is velocity?

A

Displacement travelled per second

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23
Q

What is meant by an acceleration of 15 ms-2?

A

The velocity increases by 15 ms-1 every second

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24
Q

What does this velocity-time graph show?
(its a straight line)

A

Constant velocity

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25
Q

What does this velocity-time graph show?
(its sloping up)

A

Constant acceleration

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26
Q

What does this velocity-time graph show?
(its sloping down)

A

Constant deceleration

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27
Q

What does the area under the velocity-time graph give?

A

The distance travelled

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28
Q

Describe how to calculate acceleration from a velocity-time graph

A

Pick 2 points on the slope
u = initial speed, read it off the graph
v = final speed, read it off the graph
t = time to go from the initial speed to the final speed
Calculate acceleration using a = (v-u)/t

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29
Q

What are the 3 effects a force can have?

A

Change the speed of an object
Change the direction of travel of an object
Change the shape of an object

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30
Q

What is a balanced force?

A

Equal forces acting in opposite directions

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31
Q

Newtons 1st Law is about balanced forces. What 2 things can happen if a balanced force acts on an object?

A

Remains at rest (stationary)
Travels at a constant speed in a straight line

32
Q

An object travels at a constant speed of 10 ms-1. What can be said about the forces acting on it?

A

The forces are balanced

33
Q

What causes friction?

A

Two surfaces rubbing together

34
Q

What is friction?

A

A force that opposes the motion of an object

35
Q

How can you increase friction?

A

Increase the area of the rubbing surfaces
Make the surfaces rubbing together rougher
Push the surfaces together more
Increase the speed that the surfaces are rubbing together

36
Q

How can you decrease friction?

A

Decrease the area of the rubbing surfaces
Make the surfaces rubbing together smoother
Push the surfaces together less
Decrease the speed that the surfaces are rubbing together
Lubricate/oil/wax the surfaces
Streamline the object

37
Q

What is meant by streamlining?

A

Changing the shape of an object to reduce air/water resistance/drag

38
Q

Describe a streamlined shape

A

Low to the ground
Smooth
Have curves

39
Q

What will an unbalanced force cause?

A

Acceleration

40
Q

Explain how a seatbelt works in terms of Newtons Laws

A

When a car travels at a constant velocity, the forces on it are balanced (Newtons 1st Law)
If the brakes are applied, they provide an unbalanced force that stops the car (Newtons 2nd Law)
The passengers continue to travel at a constant speed in a straight line (Newtons 1st Law)
The seatbelt provides an unbalanced force to decelerate the passenger to zero without hitting the windscreen (Newtons 2nd Law)

41
Q

What is work?

A

It is the measure of the energy used to move an object over a distance using a force

42
Q

What is the difference between mass and weight?

A

Mass is a measure of the particles that make up an object, in kg and cannot vary.
Weight is a force caused by the gravitational field strength of a planet, in N and varies according to where in the universe the object is

43
Q

What is meant by gravitational field strength?

A

Force per unit mass

44
Q

An astronaut has a mass of 50kg. What will happen to the astronaut’s mass on the Moon?

A

It stays at 50kg. Mass does not change

45
Q

An astronaut has a mass of 50kg. What will happen to the astronaut’s weight on the Moon?

A

The weight will decrease as there is a lower gravitational field strength on the Moon

46
Q

How can a space rocket be slowed down in space?

A

Reverse the thrusters to provide an unbalanced force backwards and produce a deceleration

46
Q

What is the weight of an object in freefall?

A

0 Newtons

47
Q

Explain how a skydiver reaches terminal velocity

A

When the skydiver jumps out of a plane, his initial vertical velocity is zero
His weight causes him to accelerate towards the ground (Weight = Force = ma)
As the skydivers velocity increases the air resistance upwards increases too
So the unbalanced force downwards becomes less, so there is less acceleration towards the ground (Weight - air resistance = unbalanced force = ma)
Eventually the weight downwards is equal and opposite to the air resistance upwards
This is a balanced force so the skydiver reaches terminal velocity

48
Q

What does the path of a projectile launched horizontally look like?

A

Curve

48
Q

Explain why a projectile follows a curved trajectory

A

It has a constant horizontal velocity
It has a constant vertical acceleration downwards due to gravity

49
Q

Describe how a cyclist can streamline themselves

A

Crouch over the handlebars
Wear tight Lycra clothing
Specially shaped helmet

50
Q

A car is travelling at a constant velocity of 25ms-1, the engine is producing a force of 4000N. What is the size of the frictional forces acting on the car?

A

4000N backwards

51
Q

For a projectile fired horizontally, what would the horizontal velocity-time graph look like?

A

Constant horizontal velocity - therefore a straight horizontal line

52
Q

For a projectile fired horizontally, what would the vertical velocity-time graph look like?

A

It would show a constant acceleration

53
Q

Explain how a satellite stays in orbit

A

Satellite has a constant horizontal velocity
Satellite has a constant vertical acceleration due to the gravitational field strength of the planet
This gives a curved trajectory
The planet is curved so the satellite remains in orbit

54
Q

If an object is projected horizontally from a cliff, how can the height of the cliff be calculated?

A

Sketch a vertical velocity-time graph
Due to the gravitational field strength the velocity will increase vertically by 9.8ms-2
Calculate the area under the velocity-time graph
This is equal to the vertical height of the cliff

55
Q

If an object is projected horizontally or dropped, how can the vertical velocity just before it hits the ground be calculated

A

Use a = (v-u)/t
u is 0ms-1
a is 9.8ms-2
t is the time it falls for
a = (v-0)/t
v = at

56
Q

What does the gradient on a velocity-time graph represent?

A

The acceleration

57
Q

What is conservation of energy?

A

Energy cannot be created or destroyed it can only be transferred from one form to another

58
Q

When does an object have potential energy?

A

When it is lifted through a height

59
Q

When does an object have kinetic energy?

A

When it is moving

60
Q

When is work done?

A

When a force is exerted over a distance

61
Q

Explain the energy change as a sledge slides down a hill

A

At the start, the sledge has potential energy
As it starts to slide down the hill, it loses potential energy and gains kinetic energy
At the bottom of the hill, the sledge has no potential energy as it has all been transferred to kinetic energy
At any point on the slope, the potential energy + the kinetic energy = potential energy at the top of the slope

62
Q

What is newtons first law

A

if a body is at rest or moving at a constant velocity in a straight line, it will remain at rest or at a constant velocity in a straight line unless an unbalanced force is acted upon it.

63
Q

What is newtons second law

A

Force = mass x acceleration
F = ma
Where F is Force in Newtons (N)
m is mass in kilograms (kg)
a is acceleration in (ms^-2)

64
Q

What is newtons third law

A

“Every action has an equal and opposite reaction.”
A rocket is launched into space and gains thrust by the opposite force that the jet engine fuel pushes against the Earth.

65
Q

What is free fall

A

the motion of an object where gravity is the only force acting on it.

66
Q

When does terminal velocity occur

A

when a maximum velocity is reached, where the force of drag (air resistance) is balanced with the force of gravity. As these forces are balanced, there is no acceleration and so terminal velocity is reached.

67
Q

Can energy be created

A

Energy cannot be destroyed or created, only converted from one form to another

68
Q

Examples of energy

A

Light
Heat
Kinetic
Gravitational Potential
Electrical Potential
Chemical
Sound

69
Q

What is the equation for gravitational potential energy

A

Ep = m x g x h

70
Q

What is the equation for work done

A

Ew = F x d

71
Q

What is kinetic energy and what is the equation

A

Kinetic energy is the energy of movement.
Ek = 1/2 m x v^2

72
Q

Calculate horizontal motion

A

Calculate horizontal motion using s = vt

73
Q

Calculate Vertical motion

A

Calculate vertical motion using a = (v-u)/t

74
Q

Calculate Projectile motion

A

Combine these equations to answer projectile motion questions.
a = (v-u)/t
s = vt

N5 physics (8 decks)

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