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Exploring how temperature can change a material from a solid to a liquid and back.
Have you ever wondered why your delicious ice cream turns into a sticky soup if you don't eat it fast enough on a sunny day?
Everything around us is made of materials. Some are solids, like a hard ice cube. Others are liquids, like the water you drink. When we add heat to a solid like ice, it starts to change. The heat gives the tiny parts of the ice energy to move around more. Soon, the hard ice turns into flowy, liquid water. We call this process melting. For water, this happens when the temperature gets warmer than ().
1. Take one ice cube out of the freezer. 2. Place it on a warm plate on the table. 3. Watch as the heat from the room moves into the ice. 4. In a few minutes, the solid cube becomes a small puddle of liquid water.
Quick Check
What do we need to add to a solid ice cube to make it melt into water?
Answer
We need to add heat.
Freezing is the opposite of melting! When we take heat away from a liquid, it gets colder. If liquid water gets cold enough, it stops flowing and turns back into a hard, solid block of ice. We call this freezing. To make water freeze, we usually put it in a very cold place, like a freezer, where the temperature is or lower.
1. Pour liquid fruit juice into a plastic mold. 2. Place the mold into the freezer. 3. The freezer removes the heat from the juice. 4. After a few hours, the liquid juice becomes a solid, frozen treat!
Quick Check
Does water turn into ice when we add heat or remove heat?
Answer
Water turns into ice when we remove heat (make it colder).
Water isn't the only thing that can change! Many materials change from solid to liquid when they get hot. Chocolate stays solid in a cool wrapper, but it melts into a gooey liquid if you hold it in your warm hand too long. Wax in a candle is solid, but the heat from the flame turns it into liquid drips. Even some metals can melt if they get extremely hot!
1. A solid wax candle is lit with a match. 2. The flame creates a lot of heat. 3. The solid wax near the flame turns into a liquid and runs down the side. 4. As the liquid wax moves away from the heat, it cools down and turns back into a solid drip.
What is the name of the process when a solid turns into a liquid?
At what temperature does water start to freeze?
Chocolate melts because your hand is warmer than the chocolate.
Review Tomorrow
Tomorrow, try to explain to a friend why a snowman disappears when the sun comes out. Use the words 'heat' and 'melting'.
Practice Activity
With an adult, watch what happens to a stick of butter when you put it in a warm pan. Does it stay solid or become a liquid?