← Back to course
Sports Physics 6-8 / Week 04 / Game Day
6/6
Week 04 · Gravity Pulls

Game Day

Game Day: The drop race
// The force that brings every ball back down
⏱ about 20 min

Game Day: The Drop Race

Saturday at the Field, the family holds up soft things at shoulder height. A tennis ball, a sock, a foam ball, a sponge.

"On three, everyone lets go," Rocket says. "Predict first: which lands first?"

The younger cousin votes for the tennis ball. A grown-up votes for the sponge. Raven votes for a tie.

"Three!" Everything drops. Four soft thumps land almost as one.

Nova hovers above the landing spot, flashing once for the nearly single sound.

"What do you notice?" Raven asks. "Different masses, same fall."

Rocket grins. "Gravity does not care what it is pulling. It pulls everything the same way."

  1. Gravity is the force by which a planet or other body draws objects toward its center. It is always attractive.
  2. Anything with mass has gravity. More mass means more gravity, and gravity gets weaker with distance.
  3. A dropped object speeds up as it falls. On Earth it gains about 9.8 metres per second of speed every second.
  4. Without air resistance, a heavy object and a light object fall together, as the hammer and feather did on the Moon.
  5. NASA's Planetary Fact Sheet lists surface gravity: the Moon 1.6, Earth 9.8 and Jupiter 23.1.
◇ FAMILY DROP RACE
Each person picks a soft object: a tennis ball, a rolled sock, a foam ball or a sponge.
Everyone predicts which object will land first. Write the predictions down.
Stand on flat ground, hold the objects at shoulder height, and let go together on a count of three.
Listen for the landings. Repeat three times and record what you hear each time.
Talk it over: did mass change the fall? Then look up at the Moon tonight and name the force that holds it there.
For a grown-up
Drops happen only from standing height on the floor. Nobody climbs on anything to drop from higher.
Soft objects only, with toes and pets clear of the landing spot. Work outdoors or in a cleared hallway.
The gravity facts this week come from NASA Space Place, the NASA Planetary Fact Sheet and an OpenStax physics text. Read them at nasa.gov and openstax.org.
Safety first
Drop from no higher than you can reach standing on the floor.
Only soft objects are dropped, and nothing is thrown at anyone.
Keep the landing area clear. Stop if anyone is tired or hurt.
THINK IT THROUGH
  • Read the question.
  • Tap your answer.
Four soft objects of different mass are dropped together from the same height. What do you expect?
If the drop race were held on the Moon, the objects would fall:
Game Day checkTrue or false?
Gravity pulls objects toward Earth's center.?
A heavier object always lands first.?
Jupiter's surface gravity is stronger than Earth's.?
WHY THIS EXERCISEThe drop race is your family's own evidence that gravity depends on the puller, not the thing pulled.
Draw your family's drop race: four hands letting go and four objects landing together.
← Friday