Raven sets a bag of ice cubes on the kitchen scale. The screen glows with a number. She writes it in her notebook.
Rocket leans in. "When the ice melts, it will weigh less," he says. "Ice is chunky. Water is just a puddle."
"Maybe," Raven says. "What do you notice about the bag? Can anything get in or out?"
Nova scans the zipper with a thin blue beam. "Sealed tight," she reports. "Would you like a hint? Count what goes in and what comes out."
Rocket frowns at the bag. "Nothing goes in," he says slowly. "Nothing comes out."
Last week you learned that all matter is made of particles.
Here is a big rule from science. The total weight of matter stays the same when it changes form.
We say the weight is conserved. That means it is kept, not lost.
This is true even when matter seems to vanish, like sugar in water.
When matter changes, the particles move around or join in new ways.
But all the particles that were there before are still there after. None are destroyed.
Same particles means same total weight.
| Statement | True or false? |
|---|---|
| When ice melts, some of its particles are destroyed. | ? |
| The total weight of matter stays the same when it changes form. | ? |
| Sugar that seems to vanish in water still has weight. | ? |
Melted ice spreads into a flat puddle, so it may look like less.
Sugar in water seems to vanish, so it may look like nothing is there.
A scale does not care how things look. It measures the matter that is really there.
Good thinking. Rocket's guess was a great place to start, because now we can test it. Tomorrow we will add up weights.