# velocity time graphs

## acceleration and slope

In a velocity-time graph, acceleration is represented by the slope, or steepness, of the graph line. If the line slopes upward, like the line between 0 and 4 seconds in the Figure 1.1, velocity is increasing, so acceleration is positive. If the line is horizontal, as it is between 4 and 7 seconds, velocity is constant and acceleration is zero. If the line slopes downward, like the line between 7 and 10 seconds, velocity is decreasing and acceleration is negative. Negative acceleration is called deceleration. Q: Assume that another sprinter is running the same race. The other runner reaches a top velocity of 9 m/s by 4 seconds after the start of the race. How would the first 4 seconds of the velocity-time graph for this runner be different from the Figure 1.1? A: The graph line for this runner during seconds 0-4 would be steeper (have a greater slope). This would show that acceleration is greater during this time period for the other sprinter.

## plotting velocity against time

The changing velocity of the sprinteror of any other moving person or objectcan be represented by a velocity- time graph like the one in the Figure 1.1 for the sprinter. A velocity-time graph shows how velocity changes over time. The sprinters velocity increases for the first 4 seconds of the race, it remains constant for the next 3 seconds, and it decreases during the last 3 seconds after she crosses the finish line.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

the steepness of a line graph is called its slope.

``````-->  a. true

b. false
``````

if a velocity-time graph is horizontal, then velocity is

``````a) increasing.

b) decreasing.

-->  c) not changing.

d) accelerating.
``````

in the graph described in question 5, acceleration is

``````-->  a) zero.

b) positive.

c) less than 1.

d) none of the above
``````

in the graph in question 8, acceleration between seconds 2 and 4 is 10 m/s.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson