10.7 - Instantaneous Speed 10.7

Instantaneous Speed What is it? The speed at a particular moment in time. Any object moving at a constant speed covers the same distance in each time interval. Therefore, for any object moving at a constant speed, the instantaneous speed is the same at any time, and equals the constant speed (BLM 10.7 graphs 1-2 next page)

Any object moving that is accelerating covers different distances in each successive time period. (BLM 10.7 graph 3 above) Therefore, it has different instantaneous speeds depending on the particular moment in time.

From a curved distance-time graph, (i. e From a curved distance-time graph, (i.e. one in which acceleration is occuring), the instantaneous speed must be calculated from the slope of the tangent at any instant in time. (BLM 10.7 graph 4) Tangent: a straight line which touches a curve at one particular point.

From a speed-time graph, the instantaneous speed can simply be read directly from the axis at any instant in time. (BLM 10.7 graph 5)

Average Speed Calculating the average speed of a distance-time graph is done through slope calculations of the line which connects the start and finish points over the time period of interest. (see Fig. 6 p.400)

Calculating the average speed on a speed-time graph (assuming it is linear) is done by adding the two speeds over the given time period and dividing by 2: v1 + v2 2

1. Practice Worksheet (back side of ABM 24) 2. Textbook Questions: p.400-401. Quest. 1-7