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Ratios and Data 6-8 / Week 02 / Wednesday
3/6
Week 02 · Rates and Speed

Wednesday

Numbers Lab: Timed runs
// A ratio with two different units
⏱ about 20 min

Wednesday: Numbers Lab: Timed Runs

A grown-up walks the crew to the flat path behind the house, far from the road. Raven unrolls the tape measure.

"Twenty meters," she says, pressing a strip of masking tape onto the ground at each end.

Rocket bounces on his toes. "Time me. I will do it in 3 seconds."

Nova hovers at the finish line with the timer. "Walk first. Then run. We need both numbers."

Rocket walks it in 8 seconds and runs it in 4. Raven walks it in 10 and runs it in 5.

"What do you notice about your two times?" Raven asks. Rocket thinks. "Running was exactly twice as fast. For both of us!"

Your mission

Measure a 20-meter path, time a walk and a run, and turn each time into a unit rate in meters per second.

The crew's sample times are below. Yours will be different, and that is the point of a lab.

  • A tape measure or a ruler, and masking tape to mark the start and finish
  • A kitchen timer or a phone clock, and a grown-up to hold it
  • Shoes with good grip, and your Numbers Notebook
Safety first
A grown-up picks the spot: outdoors or a cleared hallway, flat ground, away from roads and traffic.
Wear shoes. Walk the path once first and move anything you could trip on.
No racing to exhaustion. Rest between runs, and stop if anything hurts.
  1. Measure 20 meters along the path and mark both ends with tape.
  2. Walk from start to finish while the grown-up times you. Write the seconds.
  3. Rest, then run the same path. Write the seconds.
  4. Divide 20 by each time to find your meters per second. Use a calculator if the answer is not whole.
  5. Repeat for everyone who wants a turn, and fill in the data table.
WhoMetersSecondsMeters per second
Rocket2082.5
Raven20102
Rocket again2045
Raven again2054
THE CREW'S SAMPLE DATA
  • Read the question.
  • Tap your answer.
Rocket walked 20 meters in 8 seconds. How many meters per second?
Rocket ran 20 meters in 4 seconds. How many meters per second?
Raven walked 20 meters in 10 seconds. How many meters per second?
Who had the fastest run in the sample data?
PREDICT FROM THE LAB
  • Read the question.
  • Tap your answer.
Rocket runs 5 meters per second. How far would he run in 9 seconds at that speed?
Raven walks 2 meters per second. How far would she walk in 30 seconds?
Raven runs 4 meters per second. How many seconds would 60 meters take her?
Number sentenceTrue or false?
20 ÷ 8 = 2.5?
20 ÷ 4 = 5?
20 ÷ 10 = 3?
20 ÷ 5 = 4?
WHY THIS EXERCISEChecking the crew's divisions is practice for checking your own.
In the sample data, Raven ran 20 meters in 5 seconds. How many meters per second? Type the number.
WHY THIS EXERCISETurning your own time into a unit rate is the heart of this lab.
Try it
Time a third trip: skipping, hopping or walking backward slowly.
Find its unit rate and add it to your table. Where does it fit between your walk and your run?
Draw your path with the start and finish marked, and write your walk time and run time on it.

Great lab work. Tomorrow Raven opens the Field Day timing log and the crew ranks every runner.

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