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Harris Academy N4 Physics > Dynamics > Flashcards

Flashcards in Dynamics Deck (31)
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1
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
2
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
3
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
4
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.

5
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.

6
Q

What is speed?

A

Distance travelled per second.

7
Q

What is acceleration?

A

change in velocity per second.

8
Q

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

A

The velocity increases by 15ms-1 every second.

9
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
10
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
11
Q

What does this speed-time graph show?

A

Constant speed

12
Q

What does this speed-time graph show?

A

Constant acceleration

13
Q

What does this speed - time graph show?

A

Constant de-acceleration

14
Q

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

A
  • Pick two pints on the slope.
  • work out the change in speed,
  • t = time to go from the initial to the final speed.
  • Then use a = ∆v/t
15
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
16
Q

What is a balanced force?

A

Equal forces acting in opposite directions

17
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
18
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

19
Q

What causes friction?

A

Two surfaces rubbing together

20
Q

How can you increase 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
21
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
22
Q

What is meant by streamlining?

A

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

23
Q

Describe a streamlined shape

A
  • Low to the ground
  • Smooth
  • Have curves
24
Q

What will an unbalanced force cause?

A

Acceleration

25
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)
26
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.

27
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.

28
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.

29
Q

Describe how a cyclist can streamline themself

A
  • Crouch over the handlebars
  • Wear tight lycra clothing
  • Specially shaped helmet
30
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

31
Q

Which line on the graph represents the largest acceleration?

A

Blue Line - it has the steepest gradient