Activity 2 Graphical Displays of

Motion

Goals:Investigate the differences between motion

with constant speed and motion with changing speed.

Learn to use the simple technology of Dot-Cars to collect motion data.

Create bar graphs and line plot graphs to illustrate constant speed motion and changing speed motion.

Learn how graphs can be used to understand an objects motion.

Use probe technology and computers to collect and graph motion data.

Average SpeedTo find average speed, you divide distance by

time

d/t = average speed

For example, if a buggy went a distance of 100cm in 5 seconds, we would divide the distance (100cm) by the time (5 seconds)…. 100 divided by 5 = 20.

Therefore, the average speed of this buggy would be 20cm/s

Constant SpeedWhen the speed of an object does not

increase or decrease, it is moving at a constant speed.

Our red and blue buggies both move at a constant speed, though the red buggy travels at a faster constant speed than the blue buggy.

Using the Dot-Car, we are able to investigate the motion of the red and blue buggies.

Constant Speed ResultsWhen the blue buggy pushed the Dot-Car, the

marks left by the Dot-Car looked like this:

The Dot-Car leaves a dot at every time-click and

each time-click is exactly the same amount of time.

The dots above tell us that the blue buggy was moving at a constant speed because they are the same distance away from each other from start to finish.

Constant Speed ResultsWhen the red buggy pushed the Dot-Car, the

marks left by the Dot-Car looked like this:

The dots above are the same distance apart, so we know that the red buggy was also moving at a constant speed.

Comparing Constant SpeedWe can learn more about an object’s motion by

looking at the dots left by the Dot-Car.

If a dot-car is moving slow, the dots will look more like dots and they will be closer together.

If the dot-car is moving faster, the dots will look more like dashes and they will be further apart.

Graphing Constant SpeedThis bar chart shows

what constant speed looks like.

You can tell that it is constant speed because the height of each bar, for each buggy, is the same.

Graphing Constant SpeedThis line graph

shows what constant speed looks like.

You can determine constant speed on a line graph because the lines are straight. If the lines had curves, it would not be constant speed.

Non-Constant SpeedWe can investigate non-constant speed, also

known as changing speed, by using the dot-car on a ramp.

If we release the dot car from the top of a ramp that is not too steep, the dot car will slowly increase in speed as it goes down the ramp.

Non-Constant Speed

If we release the dot car from the top of a ramp that is much steeper, the dot car will quickly increase in speed as it goes down the ramp.

Non-Constant SpeedThe dot-car on the first ramp will leave a dot

trail like this:Start Finish

As the dot car begins down the ramp, a dot can be seen at the beginning. As the dot-car slowly increases in speed, the dots become longer and longer dashes and they gradually get further and further apart.

This shows us speed that is increasing slowly.

Non-Constant SpeedThe dot-car that was released from the steeper

ramp will leave a dot trail that looks like this:Start Finish

As the dot car begins down the ramp, a dot can be seen at the beginning. However, as the dot-car quickly increases in speed, the dots immediately become longer and longer dashes and they quickly get further and further apart.

This shows us speed that is increasing rapidly.

Graphing Non-Constant Speed

The different heights of the bars in this chart show us non-constant speed.

If it was constant speed, the bars would be the same height.

We can also tell that the dot car moved faster on the steep ramp than the shallow ramp.

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Steep Ramp

Shallow Ramp

Graphing Non-Constant Speed

In this line graph we can see the low ramp’s curve occurs slowly just as the dot-car’s speed increased slowly.

The steep ramp’s curve occurs quickly, just as the dot-car’s speed increased quickly on the steep ramp.

Questions to Think About1. How is constant speed different from non-

constant speed? How can this difference be displayed graphically?

2. How can you tell if an object is traveling at a constant speed? ……..speeding up?......slowing down?

3. How can you illustrate constant speed and changing speed using bar graphs and line graphs?

4. How can graphs be used to understand the motion of objects?