Preliminary Physics8.4 Moving About

Graphing Motion

Distance-Time Graphs

• The gradient of the graph is speed

• A straight line means constant speed

• A curve means that the speed is changing and the object is accelerating

Describe the motion of this object.

What could it be?

Displacement-Time Graphs

• The gradient of the graph is velocity,

• A straight line means constant velocity,

• A curve means that the velocity is changing and the object is accelerating,

• A positive gradient (sloping to the right) means positive velocity, and

• A negative gradient (sloping to the left) means negative velocity.

Describe the motion of this object.

What could it be?

Velocity-Time Graphs

• The gradient of the graph is acceleration

• A straight line means constant acceleration

• A positive gradient means positive acceleration

• A negative gradient means negative acceleration

• The area under the graph is the displacement

• An area above the x-axis is positive displacement

• An area under the x-axis is negative displacement

Describe the motion of this object.

What could it be?

Describe the motion of this object.

What could it be?

These graphs show how distance, velocity and acceleration all vary with time for the same moving object.

Example 1

a) Which runner won the race?

b) Which runner stopped for a rest?

c) How long was the stop?

d) How long did Bob take to complete the race?

e) Calculate Albert’s average speed.

Example 2

a) During which section did the bus have the greatest positive acceleration and what was it?

b) During which section did the bus have the greatest negative acceleration and what was it?

c) How far did the bus travel in 25 s?

Velo

city

(ms-1

)

Example 3

For a ball dropped from a height of 1.0 m, draw

a) a displacement- time graph

b) a velocity-time graph

c) an acceleration-time graph.