The ticker timer. A ticker timer marks a dot on a paper tape at equal time intervals while the tape is pulled along by the moving object. A school ticker timer makes 50 dots every second; here the car leaves a dot every 1 s or every 0.5 s so that the dots are easy to see.
Reading the dots. The gap between two dots is the distance travelled in one interval. Equal gaps mean a constant velocity. Gaps that grow mean the car is accelerating; gaps that shrink mean it is decelerating. Dots on top of each other mean the car is stationary.
From the tape to the graphs. Velocity = gap ÷ time between dots. The change in velocity between neighbouring gaps, divided by the time interval, is the acceleration. On the velocity–time graph, the gradient is the acceleration and the area under the line is the displacement.
Reversing. When the velocity is negative, the car moves backwards and the displacement decreases. The dots for that part of the journey are drawn hollow and on a lower row so that they do not hide the earlier dots.
The model. The velocity changes in straight lines between the points you set at each whole second, so the acceleration is constant within each second. The velocity can never jump instantly from one value to another, just as a real car cannot.
