Motion graphs: distance-time and velocity-time
Follow a car moving steadily, speeding up, slowing down or parked, record its position and speed each second, and plot motion graphs.
Core concept
The slope of a distance-time graph is velocity; the slope of a velocity-time graph is acceleration
Topic: Motion
Motion is uniform when an object covers equal distances in equal times, and non-uniform when it speeds up or slows down. A distance-time graph shows where the object is at each moment: a straight sloping line means a steady speed: How far something travels in a certain time, like kilometres per hour. All key words, a curve that gets steeper means speeding up, and a flat line means the object is not moving. A velocity-time graph shows how fast it is going: a flat line means steady velocity, and a sloping line means acceleration. Acceleration = change in velocity ÷ time taken, a = (v − u) ÷ t, measured in m/s².
What you will learn
- Plot distance-time and velocity-time graphs from measurements.
- Tell uniform from non-uniform motion using the graphs.
- Calculate acceleration from a change in velocity, a = (v − u) ÷ t.
Before you start
- Know that speed = distance ÷ time.
Materials
- Data from a car on a straight road
Equipment
- Stopwatch and distance markers (a light gate or video in a real investigation)
Procedure
- Choose the steady car. Move the time slider and record the position and speed at least four times between 0 s and 10 s.
- Repeat for the car that speeds up.
- Choose the car that slows down and find the moment it stops.
- Compare the shapes of the lines on both graphs.
How this simulation is simplified
- The road is straight and the car never reverses.
- Each car keeps a constant acceleration.