# Dynamics Flashcards

## To learn the content of the dynamics section.

Describe how to measure average speed.

- 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

Describe how to measure average speed using the equipment below.

- 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

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

- 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

Explain the difference between average and instantaneous speed.

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

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

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

What is speed?

Distance travelled per second.

What is acceleration?

change in velocity per second.

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

The velocity increases by 15ms^{-1} every second.

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

- 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

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

- 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

What does this speed-time graph show?

Constant speed

What does this speed-time graph show?

Constant acceleration

What does this speed - time graph show?

Constant de-acceleration

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

- 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

What are the three effects a force can have?

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