GCSE Physics: P9 - Motion

What is distance?

- distance tells us how far an object moves

- but it does not involve direction

What type of quantity is distance?

- distance is a scalar quantity

- as it has magnitude but no direction

What is displacement?

- displacement tells us the distance that an object moves in a straight line from the start point to the finish point

- displacement must include a direction for the straight line

What type of quantity is displacement?

- displacement is a vector quantity

- as it includes both magnitude and direction

What is speed?

the distance an object travelled in a given time

What type of quantity is speed?

- speed is a scalar quantity

- as it does not involve direction

State the equation for calculating speed

speed (m/s) = distance (m) / time (s)

v = s/t

What is the unit for speed?

m/s

What is the unit for distance?

m

What is the unit for time?

s

What symbol is used to represent speed in an equation?

- speed is represented with v

- distance is represented as s

- time is represented as t

What is normal walking speed?

normal walking speed is ~ 1.5 m/s

What is running speed?

running speed is ~ 3 m/s

What is cycling speed?

cycling speed is ~ 6 m/s

Describe the factors affecting speed

- a younger, fitter person will likely have a faster speed than an older or unfit person

- speed can depend on terrain: people can move more rapidly on flat ground than moving uphill

- speed depends on distance travelled: people tend to run at a faster speed at the start of the distance they are running as they are less tired

What is the speed of a car on a main road?

Car on main road ~ 13 m/s

What is the speed of a fast train in the UK?

Fast train in the UK ~ 50 m/s

What is the speed of a cruising aeroplane?

Cruising aeroplane ~ 250 m/s

What is the speed of sound in air?

Speed of sound in air = 330 m/s

Explain why the speed of sound in air can vary

- the speed of sound in air can vary from 330 m/s

- E.g. sound travels faster on warmer days than cooler days

Explain why scientists calculate average speed over the total length of the journey

- the speed of a moving object is rarely constant

- E.g. a car slows down and speeds up at different points during a journey

- because of this, scientists calculate average speed over the total length of the journey

What is velocity?

an object's speed in a given direction

What type of quantity is velocity?

- velocity is a vector quantity

- as it includes both magnitude and direction

How is velocity measured?

- velocity is measured as a value in m/s

- but we must also include a compass direction

State the equation for calculating velocity

velocity (m/s and a direction) = distance (m) / time (s)

v = s/t

Describe the motion of an object constantly moving in a circle

- object moving in a circle at a constant speed will have a direction that is always changing

- so the object's velocity is also changing

If an object moves at a constant speed in a circle or around a corner, its velocity is constantly changing even though its speed is constant

What are distance-time graphs?

- if an object moves along a straight line, its distance travelled can be represented by a distance-time graph

Describe the steps in constructing a distance-time graph

- the first point on the distance-time graph must be at 0

- place the points given onto the distance-time graph

- connect these points by drawing straight lines

How can we use the gradient of a distance-time graph?

- the gradient of a distance-time graph tells us the object's speed

State the equation for calculating the gradient of a distance-time graph

gradient (m/s) = distance travelled / time taken

What will the distance-time graph look like for an object constantly accelerating?

- if an object's distance-time graph has a line that is an upward, sloping curve,

- the object is constantly increasing in the speed/ accelerating

Describe the steps for determining the speed of a constantly accelerating object at a certain time using a distance-time graph

- place a dot at the certain time on the distance-time graph

- draw a tangent to the line from this dot

- calculate the gradient in m/s using the tangent:

gradient (speed) = y2 - y1 / x2 - x2

or

gradient (speed) = change in y / change in x

On a distance-time graph, the distance (m) should be on the ___________

- distance (m) should be on the y axis of the distance-time graph

On a distance-time graph, the time (s) should be on the __________

- time (s) should be on the x axis of the distance-time graph