Unit 2, Lesson 9
Constant Speed
Grade 6
9.2
Activity
Your teacher has set up a straight path with a 1-meter warm-up zone and a 10-meter measuring zone. Use the path and the following instructions to collect the data.
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- The person with the stopwatch (the “timer”) stands at the finish line. The person being timed (the “mover”) stands at the warm-up line.
- On the first round, the mover starts moving at a slow, steady speed along the path. When the mover reaches the start line, the mover says, “Start!” and the timer starts the stopwatch.
- The mover keeps moving steadily along the path. When the mover reaches the finish line, the timer stops the stopwatch and records the time, rounded to the nearest second, in the table.
- On the second round, the mover follows the same instructions, but this time, moving at a quick, steady speed. The timer records the time the same way.
- Repeat these steps until each person in the group has gone twice: once at a slow, steady speed, and once at a quick, steady speed.
your slow moving time (seconds) your fast moving time (seconds)
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After you finish collecting the data, use the double number line diagrams to answer the questions. Use the times that your partner recorded when you were the person moving.
Moving slowly:
Moving quickly:
- Estimate the distance in meters that you traveled in 1 second when moving slowly.
- Estimate the distance in meters that you traveled in 1 second when moving quickly.
- How is the diagram that represents you moving slowly different from the diagram that represents you moving quickly?
Student Lesson Summary
Suppose a train traveled 100 meters in 5 seconds at a constant speed, or at the same speed at all times.
To find its speed in meters per second, we can create a double number line:
The double number line shows that the train’s speed was 20 meters per second.
We can also find the speed by dividing: .
Once we know the speed in meters per second, many questions about the situation become simpler to answer because we can multiply the amount of time an object travels by its speed to get the distance. For example, at this rate, how far would the train go in 30 seconds? Because , the train would go 600 meters in 30 seconds.
When an object moves at a constant speed, it moves at the same speed at all times. It does not move faster or slower at any time. So, the ratios of distance traveled to elapsed time are always equivalent.
For example, a car moves at a constant speed of 50 miles per hour. This means it travels 50 miles in 1 hour, 100 miles in 2 hours, and 150 miles in 3 hours. The ratios of distance in miles to time in hours are equivalent.