# Dynamics Flashcards

What does this velocity-time graph show?

Constant velocity

How can you increases friction?

- 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

Describe how a cyclist can streamline themself

- Crouch over the handlebars
- Wear tight lycra clothing
- Specially shaped helmet

What is a balanced force?

Equal forces acting in opposite directions

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

- Remains stationary
- Travels at a constant speed in a straight line

What is acceleration?

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

What is the difference between distance and displacement?

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.

Which line on the graph represents the largest acceleration?

Blue Line - it has the steepest gradient

What is the difference between mass and weight?

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.

What is speed?

Distance travelled per second.

Name three vector quantities

- Displacement
- Velocity
- Acceleration
- Force
- Momentum
- Weight

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

It stays at 50kg. Mass does not change.

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

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

What is meant by gravitational field strength?

Force per unit mass

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

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

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.

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

- 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.

What will an unbalanced force cause?

Acceleration

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 the area under this velocity time graph give?

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

What is work?

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

How can a space rocket be slowed down in space?

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