3.1 Motion

What is displacement?

The distance travelled in a particular direction, distance is it’s scalar version

What is velocity?

The Δ of displacement, speed is it’s scalar version

What is acceleration?

The Δ of velocity, magnitude is it’s scalar version

What is instantaneous speed?

The change in distance at one particular instant of time

What is average speed?

Total distance travelled divided by the total time taken

In a displacement–time graph, how do you calculate velocity?

Find the gradient

In a velocity–time graphs, how do you calculate acceleration?

Find the gradient

In a velocity–time graphs, how do you calculate displacement?

Find the area

In a acceleration–time graphs, how do you calculate velocity?

Find the area

What does a negative gradient indicate in an acceleration–time graph?

The object is slowing down

What does a distance-time graph show?

The change in total distance travelled by the time

What does a negative displacement indicate in a displacement-time graph?

The distance travelled is opposite to what it was originally

What does a negative gradient indicate in a displacement-time graph?

The object is moving backwards

What does a straight line indicate in a displacement-time graph?

Constant velocity

What does a curved line indicate in a displacement-time graph?

Acceleration

What does a speed-time graph show?

How the speed of an object changes with time (it is always positive)

What does a velocity-time graph show?

How the velocity of an object changes with time

What does a negative velocity indicate on a velocity-time graph?

The object is moving backwards or downwards

What does a straight line indicate on a velocity-time graph?

Constant acceleration

What does a horizontal line indicate on a velocity-time graph?

Constant velocity and zero acceleration

When can you use a SUVAT equation?

When acceleration is constant

What can be used to reduce random errors due to human reaction times when calculating g?

A light gate attached to a data logger

How can uses trap doors calculate g?

When a button is pressed, electromagnets can open the doors, releasing the ball bearing and simultaneously starting an electronic timer. Once the ball passes through the other trapdoor, the timer is stopped

What is stopping distance?

The total distance travelled from the moment the driver sees the hazard until the car’s velocity is reduced to zero (thinking distance + braking distance)

What is thinking distance?

The distance travelled between the driver spotting a hazard and applying the brakes

What is braking distance?

The distance travelled after the brakes are applied until the vehicle stops

How do you calculate average acceleration?

As the acceleration is changing, you cannot use SUVAT ∴ differentiate displacement (or distance / time)

What is the vertical acceleration in free fall?

9.81

What is the horizontal acceleration in free fall?

0

What is the velocity at an objects maximum height?

0

Why can’t SUVAT be applied to the motion of a sky diver?

Because the acceleration isn’t constant

What is a projectile?

An object in free fall / an object that is only acted on by weight

What is drag?

A frictional force experienced by an object travelling through a fluid

How does speed affect drag?

The higher the speed, the more drag (often proportional to v² at high speeds)

How does area affect drag?

Larger area perpendicular to motion → greater drag

What is terminal velocity?

This the maximum velocity that the object can have, where the weight is equal to the drag and acceleration is 0

How can you calculate terminal velocity?

By measuring the time taken for a sphere to fall through a viscous liquid (e.g glycerol), and use rubber bands to see the distance traveled, steadily increasing the distance for each turn. Then draw a velocity time graph to visuallise when the velocity stopped changing.