Vel

ocit

y

Time

•Any lines above the x-axis represent positive velocities, (regardless of their slope).

positive velocities

•Lines below the axis represent negative velocities.

negative velocities

•The slope of a straight line represents acceleration.

Velocity-Time GraphsVelocity-Time Graphs

For each of the following graphs, describe the motionthat is taking place:

a)

Vel

ocit

y

Time

•positive velocitypositive velocity•positive accelerationpositive acceleration

b)

Vel

ocit

y

Time

•positive velocitypositive velocity•negative accelerationnegative acceleration

c)V

eloc

ity

Time

d)

Vel

ocit

y

Time

e)

Vel

ocit

y

Time

f)

Vel

ocit

yTime

•neg velneg vel•neg accelneg accel

•neg velneg vel•pos accelpos accel

•neg velneg vel•zero accelzero accel

•Pos, then neg velPos, then neg vel•Neg accelNeg accel

To Summarize:

How to find... from a v-t graph:

1. Instantaneous VelocityInstantaneous Velocity - Read off graph.

2. Instantaneous AcclerationInstantaneous Accleration - Slope of straight line.

3. Average AccelerationAverage Acceleration - (This is the accel between two points in time)

Draw a line between the two points. Find the slopeof this line.

4. Displacement - Displacement - •Determine the area between the line and the x-axis.•Any areas above the x-axis are positive displacements.•Areas below are negative displacements.

Vel

ocit

y

Time+

-

•Add the positive and negative areas together.

5. DistanceDistance - Same as displacement, but all areasare positive.

6. Average VelocityAverage Velocity - Displacement divided by time.

7. Average SpeedAverage Speed - Distance divided by time.

Example #1