Monday
Monday: What Does a Moving Ball Carry?
Rocket sets a paper cup on its side at the end of the driveway. He rolls a tennis ball slowly toward it.
The ball bumps the cup. The cup slides a hand's width and stops.
"Again, faster," he says, and rolls hard. The cup skids down the driveway, far past the first mark.
Raven lays the tape measure beside the two marks. "What do you notice? Same ball, same cup, different slide."
Nova traces a soft line of light behind where the ball rolled. "What did the fast ball have more of?" she asks.
"Speed," Rocket says. "And it gave some of it to the cup."
"Scientists say the moving ball has energy," Raven says. "And the faster it moves, the more it carries."
Nova hums. "Energy of motion has a name. Let us find it."
Kinetic energy: the energy of motion
A moving object can push, move or warm other things. Scientists say the moving object has energy.
The energy an object has because it is moving is called kinetic energy. The name was given in the 1700s to "the energy of motion."
A rolling ball has kinetic energy. So does a running person, a falling leaf and a spinning wheel.
When the ball hit the cup, some of the ball's kinetic energy was transferred to the cup. The cup began to move.
Scientists measure energy in a unit called the joule. A thrown tennis ball carries a few tens of joules.
- More speed means more kinetic energy.
- More mass at the same speed means more kinetic energy.
- A stopped object has no kinetic energy at all.
- Kinetic energy can be transferred from one object to another when they push on each other.
- Read the question.
- Tap your answer.
Energy moves from object to object
Think about a line of identical balls touching each other, like the toy with swinging steel balls on strings.
A physics text describes it. One ball hits an identical ball at rest. The first ball stops, and the second moves off with the first ball's speed.
The kinetic energy did not vanish. It was transferred from the first ball to the second.
At the Field, the ball gave energy to the cup. Then friction between the cup and the driveway slowed the cup to a stop.
The cup's kinetic energy did not vanish either. Friction turned it into warmth in the cup and the ground. Week 8 looks at that closely.
| Statement | True or false? |
|---|---|
| A moving ball has kinetic energy. | ? |
| A ball sitting still has a lot of kinetic energy. | ? |
| When a rolling ball hits a cup, energy can transfer to the cup. | ? |
| Kinetic energy is measured in metres. | ? |
Roll the same ball faster. Mark the new stopping place.
Write both marks in your Field Log with the words "slow" and "fast."
A driveway, hallway or patio works. Nothing is thrown, and nothing rolls toward a road or stairs.
The kinetic energy facts come from OpenStax physics texts hosted by LibreTexts and from the Next Generation Science Standards.
Good start. Tomorrow you will see exactly how speed and mass change kinetic energy, and why speed matters more.