## Wednesday, June 24, 2009

### Speed-Time Graph

Continued with the topic of distance-time graph with my 5KA girls today. We discussed a couple of questions on the topic. Most of the students were able to solve the problems given (I wish they can do the same in the next test). Then I managed to introduce the speed-time graph.

Speed-Time Graph

We can represent the movement of objects using a graph, usually plotting time on the x-axis (horizontal) and the speed on the y-axis (vertical).

Consider a train accelerating from a station along a straight and level track to a maximum speed and slowing down to a stop at the next station. The easiest way to show this is with a speed time graph.

Acceleration is the gradient of the speed-time graph.

From the graph,

* between O and A, the train is accelerating;
* between A and B, the train travels at a constant speed;
* between B and C, the train slows down. Slowing down can also be called
negative acceleration, or deceleration. It is given a minus sign.

Distance is the area under the speed-time graph. To work out the total distance, we would add the areas of:

* triangle OAX;
* rectangle ABXY;
* triangle BCY.