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A fun comparison lesson to help students tell the difference between solids and liquids.
If you put a toy car in a bowl, it stays a car—but if you pour milk into a bowl, it changes its whole shape! Why does some stuff stay the same while other stuff moves around?
A solid is something that likes to keep its shape. Think of your favorite building block. If you hold it in your hand, it is a square. If you put it in a backpack, it is still a square! This happens because the tiny parts inside a solid are packed together very tightly. They are like friends holding hands so tight they cannot move. Whether you have block or blocks, they won't flow or spread out on the floor like water does.
Let's look at an apple: 1. Pick up the apple. It feels hard and has a round shape. 2. Put the apple inside a square lunchbox. 3. Look at the apple again. Is it a square now? No! It is still round. 4. Because it kept its shape, the apple is a solid.
Quick Check
If you move a pencil from your desk into a cup, does the pencil change its shape?
Answer
No, the pencil stays the same shape because it is a solid.
A liquid is a shape-shifter! Liquids do not have a shape of their own. Instead, they take the shape of whatever container they are in. If you pour water into a round fishbowl, the water becomes round. If you pour it into a square tray, it becomes square. The tiny parts inside a liquid are not holding hands tightly; they are sliding and gliding past each other. This is why liquids can flow and splash!
Imagine a glass of orange juice: 1. In the tall glass, the juice looks like a tall cylinder. 2. Oops! The glass tips over on the flat table. 3. The juice spreads out into a wide, flat puddle. 4. Because the juice changed from 'tall' to 'flat' to fit the table, it is a liquid.
Quick Check
What is one thing a liquid can do that a solid cannot?
Answer
A liquid can flow or change its shape to fit a container.
Some things try to trick us! Think about sand. You can pour sand into a bucket just like water. Does that make it a liquid? No! If you look through a magnifying glass, you will see that sand is actually thousands of tiny, tiny little rocks. Each grain of sand is a solid because that one little grain never changes its shape. Jelly is also tricky because it wobbles, but since it stays together in one piece, we usually treat it like a solid that is very soft!
How do we know sand is made of solids? 1. Take one single grain of sand. 2. Try to put it in a tiny doll-sized cup. 3. Does that one grain change shape to look like the cup? No. 4. Even though a pile of sand flows, the grains are solids. So, sand is a collection of solids!
Which of these is a solid?
What happens when you pour a liquid into a star-shaped bowl?
A single grain of sand is a liquid because you can pour a whole bucket of it.
Review Tomorrow
Tomorrow morning at breakfast, look at your drink and your plate. Can you tell which one is the solid and which one is the liquid?
Practice Activity
Go on a 'Matter Hunt' in your house! Find 3 things that keep their shape (solids) and 2 things that you can pour (liquids).