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Sports Physics 6-8 / Week 08 / Wednesday
3/6
Week 08 · Bounce, Roll and Stop

Wednesday

Field Lab: Bounce height on three floors
// Where the energy goes
⏱ about 20 min

Wednesday: Field Lab: Bounce Height on Three Floors

Rocket tapes a strip of masking tape to the wall at the height of his shoulder. "Drop line," he says. "Same for every drop."

Raven stands a tape measure against the wall beside it. "I watch the top of the bounce. You drop. Nova calls it."

Nova hovers level with the drop line. "What is the only thing you change between tests?" she asks.

"The floor," Rocket says. "Tile first, then the wooden board, then the rug."

He lets the ball go. It thumps on the tile and rises. Raven calls out a number, and Rocket writes it down.

"What do you notice?" Raven asks. "The thump sounded different on the rug."

"Softer," Rocket says. "And lower bounce. The rug took more."

Nova's light glows. "Two clues at once. Write both."

Your mission

Today you measure how much energy a bounce keeps on three different floors. The ball, the drop height and the drop line stay the same.

You record the bounce height three times on each floor and note how the thump sounded. Then you build an energy inventory from your numbers.

  • One tennis ball or other soft bouncy ball
  • Three floors: a hard tile or concrete patio, a wooden board or wood floor, and a rug or carpet
  • A tape measure or metre stick, standing upright against a wall
  • Masking tape for the drop line, at shoulder height while standing on the floor
  • A partner to watch the top of the bounce, and your Field Log
Safety first
Drop from shoulder height while standing on the floor. Never climb on anything to drop higher.
Use a soft bouncy ball only, never a hard ball. Keep the drop spot away from windows and younger children.
Let the ball finish bouncing before anyone steps in to pick it up.
  1. Tape the drop line on the wall at your shoulder height. Stand the tape measure upright beside it.
  2. Hold the ball with its bottom at the drop line and let it go. Do not push it down.
  3. Your partner watches the bottom of the ball at the top of the first bounce and reads the height.
  4. Write the bounce height and one word for the sound, such as sharp or soft.
  5. Repeat twice more on the same floor.
  6. Move to the wooden board and repeat three drops from the same drop line height.
  7. Move to the rug and repeat three drops.
  8. For each floor, write the best bounce as a fraction of the drop height. Half the drop height is 50 percent.
PREDICT BEFORE YOU DROP
  • Read the question.
  • Tap your answer.
Which floor do you expect to give the highest bounce?
On which floor will the most of the ball's energy become thermal energy and sound?
Why does the drop line stay at the same height for every test?
FloorBounce 1 (cm)Bounce 2 (cm)Bounce 3 (cm)Best bounce as percent of dropSound
Hard tile or concrete
Wooden board
Rug or carpet

Reading the result

Every drop started with the same stored energy, because the drop height never changed. The floor decided how much came back as height.

The percent you wrote is your bounce share. The rest of the energy became thermal energy in the ball and floor, and sound in the air.

A lower bounce means a bigger share went to warmth and sound. The softer thump on the rug is part of the same story.

The physics text gives 0.72, or 72 percent, for a new tennis ball on a court. Your tile result may be close to that, or lower.

Your three drops on one floor should be close. Your partner's eye is the biggest source of error, so repeating helps.

What the lab showsTrue or false?
Every drop started with the same stored energy.?
A lower bounce means more energy became thermal energy and sound.?
The ball bounced higher than the drop line on at least one floor.?
The floor had no effect on the bounce height.?
WHY THIS EXERCISEThe floor is the variable, and the missing height is your evidence of where the energy went.
Draw three bars for your three floors, each as a percent of the drop height. Shade the missing part of each bar and label it.

Careful measuring. Tomorrow you will read a real table that shows how much energy machines and athletes turn into useful work.

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