Monday
Monday: Same Push, Different Ball
Rocket lines up a foam ball and a heavy playground ball on the driveway. "Same push for each," he says. "Watch."
He gives the foam ball a gentle shove. It skitters across the driveway and bumps the fence.
He gives the playground ball the same shove. It rolls a short way and stops.
"What do you notice?" Raven asks. "You pushed the same, but the balls did different things."
"The light one flew. The heavy one barely moved," Rocket says. "The push was the same. The ball was not."
Nova hovers between the two balls. "What is different about them? Not the size, not the color."
Rocket lifts both. "How much stuff is in them. The heavy one has more."
Mass is how much matter
A physics text from OpenStax defines mass as a measure of the amount of matter, or stuff, in an object.
The amount of matter depends on the number and types of atoms the object contains.
The SI unit of mass is the kilogram, one of the seven base units described by NIST.
A playground ball has more mass than a foam ball of the same size. It has more matter packed inside.
OpenStax adds that the inertia of an object is proportional to its mass. More mass means more resistance to a change in motion.
| Object at the Field | More mass or less mass? | How it answers one gentle push |
|---|---|---|
| Foam ball | less mass | speeds up a lot, rolls far |
| Tennis ball | more than foam | speeds up less than the foam ball |
| Heavy playground ball | most mass of the three | speeds up least, rolls a short way |
- Read the question.
- Tap your answer.
More mass, less change
OpenStax puts it with a picture. Changing the motion of a large truck is more difficult than changing the motion of a toy truck.
The Next Generation Science Standards say it this way. The greater the mass, the greater the force needed for the same change in motion.
Rocket's push was the same each time. The foam ball, with less mass, changed its motion a lot.
The playground ball, with more mass, changed its motion only a little. Same push, different mass, different result.
| Statement | True or false? |
|---|---|
| Mass is a measure of the amount of matter in an object. | ? |
| A foam ball and a heavy ball get the same change in motion from the same push. | ? |
| More mass means more inertia. | ? |
| Changing the motion of a toy truck is harder than changing the motion of a large truck. | ? |
Give each the same gentle push from the same tape line on a smooth floor. Watch which goes farther.
Write both results in your Field Log with the word mass.
Soft balls only: foam, tennis or a playground ball. Everything rolls along the ground; nothing is thrown.
The mass and weight facts come from an OpenStax physics text, NASA and NIST, which you can read at nasa.gov and nist.gov.
Good observing. Tomorrow you will learn the rule that links force, mass and the change in motion.