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The simplest type of motion (excluding the trivial case in which the body under
investigation remains at rest) consists of motion with constant velocity.
This type of motion occurs in everyday life whenever an object slides over a horizontal,
low friction surface: e.g., a puck sliding across a hockey rink.
Fig. 6 shows the graph of displacement versus time for a body
moving with constant velocity. It can be seen that the graph consists of
a straightline. This line can be represented algebraically as

(18) 
Here, is the displacement at time : this quantity can be determined from the
graph as the intercept of the
straightline with the axis. Likewise, is the constant velocity of
the body: this quantity can be determined from the graph as the gradient of the straightline
(i.e., the ratio
, as shown). Note that
, as expected.
Figure 6:
Graph of displacement versus time for a body moving with constant velocity

Fig. 7 shows a displacement versus time graph for a slightly more
complicated case of motion with constant velocity. The body in question moves
to the right (since is clearly increasing with ) with a constant velocity (since
the graph is a straightline) between times and . The body then moves to
the right (since is still increasing in time) with a somewhat larger constant velocity
(since the graph is again a straight line, but possesses a larger gradient than before) between times
and . The body remains at rest (since the graph is horizontal) between times and .
Finally, the body moves to the left (since is decreasing with ) with a constant
velocity (since
the graph is a straightline) between times and .
Figure 7:
Graph of displacement versus time

Next: Motion with constant acceleration
Up: Motion in 1 dimension
Previous: Acceleration
Richard Fitzpatrick
20060202