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
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
An object travels at a constant speed of 10ms-1. What can be said about the forces on it?
The forces are balanced
What causes friction?
Two surfaces rubbing together
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
How can you decrease friction?
- 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
What is meant by streamlining?
Streamlining is changing the shape of an object to reduce air/water resistance
Describe a streamlined shape
- Low to the ground
- Smooth
- Have curves
What will an unbalanced force cause?
Acceleration
