How can we describe motion?
You should be able to draw and explain distance-time graphs for objects moving at steady speeds or standing still.
The vertical axis of a distance-time graph is the distance travelled from the start, and the horizontal axis is the time taken from the start.
When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed, the line on the graph is straight, but sloped.
The diagram shows some typical lines on a distance-time graph.
Note that the steeper the line, the greater the speed of the object. The blue line is steeper than the red line because it represents an object moving faster than the object represented by the red line.
The red lines on the graph represent a typical journey where an object returns to the start again. Notice that the line representing the return journey slopes downwards.
Changes in distances in one direction are positive, and negative in the other direction. If you walk 10m away from me, that can be written as +10m; if you walk 3m towards me, that can be written as –3 m.
Watch this illustrated podcast for more on speed and distance-time graphs.
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