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Sports Physics 6-8 / Week 06 / Game Day
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Week 06 · Kinetic Energy: Mass and Speed

Game Day

Game Day: Cup slide contest
// The energy of motion
⏱ about 20 min

Game Day: Cup Slide Contest

Saturday morning, three paper cups lie on their sides at the end of the driveway, one for each person.

"Same ball, same start line," Rocket announces. "Roll it, and your cup slide is your score."

Raven writes names and a column for centimetres. "One rule: roll, never throw. Fast rolls only on the ground."

Nova hovers above the start line like a tiny referee. "What makes a cup slide farther?" she asks.

"More kinetic energy in the ball," Rocket says. "Which means more speed."

The first roll skims down the driveway and sends the cup tumbling. Raven stretches the tape measure.

"What do you notice?" she asks. "The ball nearly stopped. The cup got its energy."

Nova's light glows. "Now see who can transfer the most."

  1. Kinetic energy is the energy of motion. Only moving things have it.
  2. Kinetic energy is proportional to mass: double the mass, double the energy.
  3. Kinetic energy grows with the square of speed: double the speed, four times the energy.
  4. Energy is measured in joules. A thrown tennis ball carries tens of joules, and a sprinter thousands.
  5. When a moving ball hits a cup, energy transfers to the cup. Friction then turns the cup's motion into warmth.
◇ FAMILY CUP SLIDE
Tape a start line on a driveway, patio or hallway. Lay one paper cup per person on its side, open end toward the line.
Each person rolls the same soft ball from the start line into their cup, as fast as they like, rolling only.
Measure each cup slide with a tape measure. Reset the cup and roll two more times each.
Try one round with a heavier soft ball from the same line. Does every cup slide farther?
Talk it over. Who transferred the most energy? What did they do differently with their roll?
For a grown-up
Rolling only, never throwing. Soft balls only: a tennis ball, foam ball or playground ball.
Pick a lane away from roads, stairs, windows and younger children. Shoes on outdoors.
The kinetic energy ideas this week come from OpenStax physics texts, which you can read at openstax.org.
Safety first
Roll the ball along the ground. Never throw it.
Keep the lane clear while a ball is moving.
Stop if anyone is hurt or tired, and drink water on a hot day.
THINK IT THROUGH
  • Read the question.
  • Tap your answer.
Two rolls use the same ball. One cup slides much farther. What was different about the winning roll?
A heavier ball at the same speed hits the cup. What happens to the slide?
Game Day checkTrue or false?
The cup slides because kinetic energy was transferred to it.?
A ball rolling twice as fast has twice the kinetic energy.?
Friction with the ground is what finally stops the cup.?
WHY THIS EXERCISEThe cup contest is the whole week in one roll: speed, transfer and friction.
Draw your family's three cups at their stopping places. Label the longest slide and write what made it win.
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