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JGHS - N5 Physics (even more) > Dynamics > Flashcards

Dynamics Flashcards

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1
Q

What does this velocity-time graph show?

A

Constant velocity

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2
Q

How can you increases friction?

A
  • Increase the area of the rubbing surfaces
  • Make the rubbing surfaces rougher
  • Push the rubbing surfaces togerther more
  • Increase the speed that the surafces are rubbed together
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3
Q

Describe how a cyclist can streamline themself

A
  • Crouch over the handlebars
  • Wear tight lycra clothing
  • Specially shaped helmet
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4
Q

What is a balanced force?

A

Equal forces acting in opposite directions

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5
Q

Newtons 1st Law is about balanced forces, what two things can happen if a balanced force acts on an object?

A
  • Remains stationary
  • Travels at a constant speed in a straight line
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6
Q

What is acceleration?

A

Acceleration is the rate of change of velocity or the change in velocity per second.

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7
Q

What is the difference between distance and displacement?

A

Distance is the length of the path you actually take and it is a scalar, displacement is the straight line distance between where you started and finished including a direction as it is a vector.

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8
Q

Which line on the graph represents the largest acceleration?

A

Blue Line - it has the steepest gradient

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9
Q

What is the difference between mass and weight?

A

Mass is a measure of the partcles that make an object up. Weight is a force caused by the gravitational field strength of a planet.

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10
Q

What is speed?

A

Distance travelled per second.

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11
Q

Name three vector quantities

A
  • Displacement
  • Velocity
  • Acceleration
  • Force
  • Momentum
  • Weight
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12
Q

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

A

It stays at 50kg. Mass does not change.

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13
Q

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

A

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

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14
Q

What is meant by gravitational field strength?

A

Force per unit mass

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15
Q

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

A

The velocity increases by 15ms-1 every second.

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16
Q

Explain the difference between average and instantaneous speed.

A

Average speed is over a long period of time, Instantaneous speed is the speed over a very short period of time.

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17
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 gravitational field strength the velocity will increase vertically by 9.8ms-1.
  • Calculate the area under the velocity-time this is equal to the verical height of the cliff.
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18
Q

What will an unbalanced force cause?

A

Acceleration

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19
Q

Explain how to measure acceleration using the equipment shown below and a stop watch.

A
  • When the cardboard passes through the first light gate the timer attached to it records this time.
  • Measure the length of the card with a ruler.
  • The initial velocity, u = length of card / time on timer
  • As the car rolls down the ramp, start the stop watch when it reaches the first light gate and when it reaches the second light gate stop the stop watch.
  • This is t, the time for the change in velocity.
  • When the cardboard passes through the second light gate the timer attached to it records this time.
  • The final velocity, v = length of card / time on timer
  • Then calculate acceleration, a = (v-u)/t
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20
Q

What does the area under this velocity time graph give?

A

If positive area and negative area are subtracted it gives the displacement. If the total area is calculated it gives the distance travelled.

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21
Q

What is work?

A

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

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22
Q

How can a space rocket be slowed down in space?

A

Reverse the thrusters to provide an unbalanced force backwards to slow you down.

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23
Q

When does an object have kinetic energy?

A

When it is moving.

24
Q

When is work done?

A

When a force is exterted over a certain distance.

25
Q

What are the three effects a force can have?

A
  • Change the speed of the object
  • Change the direction of travel of the object
  • Change the shape of the object
26
Q

How can you decrease friction?

A
  • Decrease the area of the rubbing surfaces
  • Make the rubbing surfaces smoother
  • Push the rubbing surfaces together less
  • Decrease the speed that the surfaces are rubbed together
  • Lubricate/oil/ wax the surfaces
  • Streamline the object
27
Q

What is conservation of energy?

A

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

28
Q

What happens to the object at point X?

A

It changes direction

29
Q

What does this velocity-time graph show?

A

Constant acceleration

30
Q

What is meant by streamlining?

A

Streamlining is changing the shape of an object to reduce air/water resistance

31
Q

Name three scalar quantities

A
  • Distance
  • Time
  • Speed
  • Mass
  • Energy
32
Q

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

A

The forces are balanced

33
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
34
Q

Explain how a seatbelt works in terms of Newton’s 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 backwards force to decelerate the passenger to zero without hitting the windscreen. (Newtons 2nd Law)
35
Q

What does the path a projectile takes look like?

A

Curve

36
Q

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

A

It would show a constant acceleration, a line of gradient = 9.8ms-2

37
Q

Explain the energy change as the sledge slides down the 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 sldge has no potential energy 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.
38
Q

What causes friction?

A

Two surfaces rubbing together

39
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.

40
Q

What does the gradient of the line on velocity - time graph represent?

A

The acceleration

41
Q

What does this velocity - time graph show?

A

Constant de-acceleration

42
Q

Describe a streamlined shape

A
  • Low to the ground
  • Smooth
  • Have curves
43
Q

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

A

The distance travelled

44
Q

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

A

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

45
Q

Explain how to measure the acceleration of the car using the equipment shown below and a stop watch.

A
  • Car starts from rest so u = 0ms-1.
  • When the car is released start the stop watch when it reaches the light gate stop the stop watch.
  • This is t, the time for the change in velocity.
  • When the cardboard passes through the light gate the timer attached to it records this time.
  • Measure the length of the card with a ruler.
  • The final velocity, v = length of card / time on timer
  • Then calculate acceleration, a = (v-u)/t
46
Q

What is the weight of an object in freefall?

A

0 Newtons

47
Q

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

A

Constant horizontal velocity - therefore a straight horizontal line.

48
Q

Describe how to calculate acceleration from a veocity - time graph.

A
  • Pick two pints 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 to the final speed.
  • Then use a = (v-u)/t
49
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

v you are calculating

t is the time it falls for

a = (v-0)/t

v = at

50
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.

51
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

52
Q

When does an object have potential energy?

A

When it is lifted through a height.

53
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 down becomes less, so there is less aceleration 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.
54
Q

Describe how to measure average speed using the equipment below.

A
  • Two light gates are connected to a timer.
  • The car rolls down the slope.
  • When the cardboard breaks the first lightgate beam it starts the timer. When the cardboard breaks the second lightgate beam it stops the timer.
  • The timer records the time taken to go from the first to the second light gate.
  • Measure the distance between the two light gates using a metre stick.
  • Calculate the speed = distance between light gates / time on timer
55
Q

Explain how to use the equipment below to calculate the instantaneous speed of the car.

A
  • Measure the length of the cardboard using a ruler.
  • Roll car down the slope.
  • When the cardboard breaks the beam it starts the timer connected to the light gate. When the cardboard has passed through the beam is remade and the timer stops.
  • Speed = length of cardboard / time on timer
56
Q

Describe how to measure average speed.

A
  • Mark a start line and a finish line.
  • Measure the distance between the start and finish line with a ruler/metre stick.
  • Start a stopwatch when the object crosses the start line and stop it when the object crosses the finish line.
  • Calculate the average speed = distance between start and finish / time on stopwatch
57
Q

What is velocity?

A

Displacement travelled per second.

JGHS - N5 Physics (even more) (8 decks)

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