Solids, Liquids, Heating, and Cooling

A spoon keeps its shape. Milk flows. What happens to things when they get warm or cold? Let’s find out!

This lesson takes about 15 minutes. You can take a break after each part.

Before you start

Solids, Liquids, Heating, and Cooling

Learning objectives

  • I can say if something is a solid or a liquid.
  • I can say what heating and cooling do to ice and chocolate.
  • I can say if a change can be undone or not.

Solids and liquids

Solids keep their shape

A wooden block, a rock, and a spoon are solids. Put a block in a box, in a bowl, or on the table. It keeps the same shape.

Liquids flow

Water, milk, and juice are liquids. A liquid flows when you pour it. It takes the shape of its container. A container is something that holds things, like a cup, a bottle, or a bowl.

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Heating and cooling

Heat can melt a solid

When a solid gets warm enough, it can melt. It becomes a liquid. An ice cube in the sun melts into water. Chocolate in a warm hand gets soft and runny.

Cold can freeze a liquid

When a liquid gets cold enough, it can freeze. It becomes a solid. Water in the freezer turns into ice. Melted chocolate in the fridge gets hard again.

Red arrows with flames go from an ice cube to a bowl of water to a pot of boiling water. Blue arrows with snowflakes go back the other way.
Heating turns ice into water. Cooling turns water back into ice.

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Changes we can undo, and changes we cannot

Some changes can be undone

Melted ice can freeze again. Melted butter can get hard again. We can go back to how it was before.

Some changes cannot be undone

A cooked egg never becomes raw again. Toast never turns back into soft bread. Burned paper never comes back. Heating changed them forever.

Top: a chocolate bar melts in a pan, then hardens again in a mold. Bottom: a stick burns in a fire and becomes ash.
Melted chocolate can become solid again. A burned stick cannot become wood again.

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Review game

Final assessment

To master the lesson, you need at least 60% correct answers.

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Summary

  • A solid keeps its own shape. A liquid flows and takes the shape of its container.
  • Heating can melt a solid. Cooling can freeze a liquid.
  • Some changes can be undone, like melting ice. Some cannot, like cooking an egg.

A few related activities

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