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Observing how adding heat can change a solid into a liquid.
Have you ever wondered why a delicious chocolate bar turns into a gooey mess if you leave it in your pocket on a sunny day?
Everything around us is made of matter. Some things are solids, like a rock or a toy block. Solids keep their own shape. But when we add heat, something amazing can happen! Melting is the process where a solid turns into a liquid. This happens because heat gives the tiny parts of the solid energy to move around. Instead of staying in one spot, they start to slide and flow. Imagine a group of children standing perfectly still in a line (a solid) who suddenly start dancing and moving all over the room (a liquid) because the music (heat) started!
Let's look at the most common example of melting: 1. Take a solid ice cube out of the freezer. It is very cold, around (). 2. Place it on a warm plate. 3. The heat from the air and the plate moves into the ice. 4. Slowly, the hard edges of the cube disappear, and a puddle of liquid water forms.
Quick Check
What is the 'magic ingredient' that causes a solid to turn into a liquid?
Answer
Heat is the ingredient that causes melting.
Ice isn't the only thing that melts! Many items in your house change from solid to liquid when they get warm. Chocolate is a solid that melts at a temperature just slightly lower than your body heat, which is why it melts in your mouth! Wax is another solid. When you light a candle, the flame provides heat that turns the hard wax into a runny liquid. Even butter in a hot pan will quickly turn from a yellow stick into a golden liquid. Different solids need different amounts of heat to melt.
Think about a birthday candle: 1. Before you light it, the candle is a tall, hard solid. 2. You add heat using a match to light the wick. 3. The wax near the flame gets hot and turns into a liquid that drips down the side. 4. If the liquid wax moves away from the heat, it might cool down and become a solid again!
Quick Check
Name two things besides ice that can melt when they get hot.
Answer
Chocolate, wax, or butter.
One of the biggest changes during melting is shape. A solid has its own shape and doesn't change unless you break it. If you put a square ice cube in a round bowl, it stays a square... at first! But as it melts into a liquid, it loses its old shape. Liquids are 'flowy.' They take the shape of whatever container they are in. If you melt an ice cube in a star-shaped cup, the liquid water will eventually fill up that star shape. The amount of matter stays the same, but the way it looks changes completely!
Imagine you have a chocolate bar shaped like a rectangle: 1. You put the rectangle in a heart-shaped bowl and leave it in the sun. 2. The heat melts the solid rectangle into a liquid. 3. The liquid chocolate spreads out to fill the bottom of the heart-shaped bowl. 4. Even though it's still chocolate, it is no longer a rectangle!
What happens to a solid when it melts?
Which of these needs heat to turn into a liquid?
A liquid takes the shape of the container it is in.
Review Tomorrow
Tomorrow, try to explain to a friend or family member why an ice cube gets smaller and turns into a puddle when it's left on the counter.
Practice Activity
With an adult's help, put a small piece of chocolate in your hand and close it. Wait one minute. Open your hand and see if the heat from your body started to melt the chocolate!