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Sports Physics 6-8 / Week 07 / Friday
5/6
Week 07 · Potential Energy: Height and Stretch

Friday

Stored energy in sport
// Energy that waits
⏱ about 20 min

Friday: Stored Energy in Sport

Rocket crouches low on the lawn, knees bent, then springs up and lands. "Did you see that? I stored and released."

Raven nods. "Bent knees first. Like a bent ruler. What do you notice about a high jumper right before the jump?"

"Same thing," Rocket says. "They sink down, then push off."

Nova circles above them. "And where does the energy go at the very top of a jump?" she asks.

"Stored again," Rocket says. "Height energy. Then back to motion on the way down."

Raven points at the trampoline in the neighbor's yard. "Stretched mat, stored. Jumper up high, stored. Falling, motion."

"Sport is just trading," Rocket says. "Stored, moving, stored, moving." Nova hums. "Then you are ready to review."

Trading energy in a game

A diver on a high board has gravitational potential energy. The higher the board, the more is stored and the faster the entry.

A stretched trampoline mat, a bent vaulting pole and a squeezed ball all store elastic potential energy in their shape.

The physics text says potential energy can be stored in any elastic medium by deforming it. Stretch it, squeeze it or bend it.

When the shape springs back, the stored energy becomes kinetic energy. The jumper rises, the ball leaps, the pole straightens.

At the top of a jump, kinetic energy has become gravitational potential energy again. Then gravity turns it back into motion.

Sport momentKind of stored energyWhat it becomes
A diver standing on a high boardGravitationalSpeed on the way down
A trampoline mat stretched downElasticThe jumper's upward speed
A ball squeezed flat as it hits the groundElasticThe bounce back up
A jumper at the top of a leapGravitationalSpeed as they come down
SPOT THE STORED ENERGY
  • Read the question.
  • Tap your answer.
A diver climbs to a higher board. What happens to the stored energy before the dive?
A trampoline mat is stretched down as far as it will go. Which kind of energy is stored?
At the very top of a jump, the jumper's speed is nearly zero. Where is the energy?
Week reviewTrue or false?
Potential energy is stored energy that can be recovered.?
A higher ramp stores more gravitational potential energy in a ball.?
A stretched rubber band stores elastic potential energy.?
The same lift stores the same energy on every world.?
At the bottom of a ramp a ball has its most potential energy.?
WHY THIS EXERCISEThese five ideas explain every roll, bounce and jump you watched this week.
OUR WEEK, IN ORDER
  • ?We named stored energy: potential energy.
  • ?We watched stored energy become motion and back.
  • ?We rolled a ball from one, two and three books.
  • ?We read the gravity of ten worlds from NASA.
  • ?We found stored energy in dives, jumps and bounces.
WHY THIS EXERCISESeeing the order shows how storing led to measuring and then to explaining.
Which kind of potential energy is stored in a stretched trampoline mat? Type one word.
WHY THIS EXERCISEElastic storage is the second big kind of potential energy, and it shows up in every bounce.
Try it
Stand still, then bend your knees and jump straight up on the grass. Land softly with bent knees.
Notice the pause at the top. That is stored energy.
Write "bend, push, rise, pause, fall" in your Field Log and label each with stored or motion.
Draw a jumper at four moments: crouched, pushing off, at the top and landing. Label each with stored energy or motion energy.

Great week. Tomorrow is Game Day: a family ramp contest. Next week, where the missing energy goes.

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