← Back to course
Sports Physics 6-8 / Week 03 / Friday
5/6
Week 03 · Mass Matters

Friday

Heavy gear, light gear
// The same push, a different result
⏱ about 20 min

Friday: Heavy Gear, Light Gear

Rocket fills a backpack with books and tries to push it across the grass. It barely moves.

He takes the books out and pushes again. The empty pack slides easily.

"What do you notice?" Raven asks. "Same push, same pack, same grass."

"Different mass," Rocket says. "Books in, hard to move. Books out, easy."

Nova hovers above the backpack. "Where in sport does a heavy thing help, and where does a light thing help?"

Rocket thinks. "A light ball is easy to speed up. A heavy ball is hard to stop."

Raven smiles. "Both are the same rule, pointed two ways."

Why gear mass matters

The same rule from this week explains a lot of sports gear. More mass means a smaller change in motion from the same force.

A light ball changes its motion easily. A gentle tap sends it far, and a gentle tap stops it.

A heavy ball resists. It needs a bigger force to get going, and a bigger force to stop.

OpenStax says the inertia of an object is proportional to its mass. Heavy gear has more inertia.

That is why a light player and a heavy player feel the same push differently. More mass, less change.

GearMassEasy to speed up?Easy to stop?
Foam balllowyesyes
Playground ballmediumfairlyfairly
Backpack full of bookshighnono
FORCE, MASS AND SPORT
  • Read the question.
  • Tap your answer.
A gentle tap sends a foam ball across the floor. The same tap barely moves a heavy ball. Why?
A heavy ball rolling toward you is harder to stop than a light one at the same speed because:
To speed up a loaded wagon as much as an empty one, you must:

Mass and weight on the field

When a player lifts a heavy ball, they feel its weight, the pull of gravity on its mass.

When a player pushes that ball sideways across the ground, they feel its mass resisting the change in motion.

The two are linked. On Earth, OpenStax says a 1.0 kilogram mass weighs 9.8 newtons.

On the Moon the same ball would weigh about 1.7 newtons, yet it would be just as hard to push sideways.

That is the clearest way to see that weight is a force and mass is the stuff.

Week reviewTrue or false?
Mass is the amount of matter in an object.?
For the same force, more mass means a smaller change in motion.?
A larger force on the same object causes a smaller change in motion.?
Weight is a force measured in newtons.?
An object's mass changes when it goes to the Moon.?
WHY THIS EXERCISEThese five ideas are the whole of Newton's second law, in words.
OUR WEEK, IN ORDER
  • ?We found force and mass at work in sports gear.
  • ?We read a table showing mass stays the same while weight changes.
  • ?We used a ramp launcher to give the same push to two targets.
  • ?We learned that the change in motion depends on force and mass.
  • ?We saw the same push move a light ball far and a heavy ball a little.
WHY THIS EXERCISEThe week moved from one surprising push to a rule that works on Earth and on the Moon.
A pushed object with more mass changes its motion more or less than one with less mass? Type one word.
WHY THIS EXERCISEMore mass, less change: the heart of this week.
Try it
Push an empty box across the floor with one hand. Put a few books in it and push the same way.
Write which push changed the box's motion more, and name the rule that explains it.
Draw a light ball and a heavy ball rolling toward a wall at the same speed. Show which is harder to stop with a hand.

Great week. Tomorrow is Game Day: a family push test with gear of many masses.

← Thursday