Convection in three lines: how the Tutor's board works

A board that writes as it speaks

Solver Bro’s Tutor teaches on a whiteboard that writes in step with its voice. Each line appears as it is spoken, so your child hears an idea and sees it written at the same moment. Then the Tutor asks a question back, to check the idea has landed.

The demo on our home page shows this in about ten seconds. Here it is, line by line.

Line 1: “Hot water rises”

Spoken: “Hot water is lighter, so it rises.”

When water is heated, its particles move faster and spread out a little. The same amount of water now takes up slightly more space, so it is less dense than the cooler water around it. Less dense things float up through denser ones. So the warm water rises.

On the board, the words appear first, then a small upward arrow.

The loop

Spoken: “At the top, it cools and spreads.”

The board draws a pot of water over a flame, and an arrow going up the heated side and across the top.

At the surface, the warm water gives away some of its heat to the air and to the cooler water nearby. As it cools, it becomes denser again.

Line 2: “Cool water sinks”

Spoken: “Cool water sinks back down.”

The second arrow goes down the far side of the pot and back along the bottom. The cooler, denser water sinks, reaches the bottom near the flame, gets heated, and rises again.

That full circle is a convection current. Heat is carried around the pot by the moving water itself. This is how heat travels through liquids and gases.

The question back: “What keeps it moving?”

The lesson doesn’t end with the last line. The board shows “Your turn: what keeps it moving?” and waits for your child.

The answer is the heat from the flame at the bottom. As long as the bottom keeps heating the water, warm water keeps rising and cool water keeps sinking. Turn off the flame, and the loop slows down and stops.

This is the part that matters most. Writing three lines is easy. Asking your child to use them, to explain why the loop keeps going, is what turns a picture into understanding. You can read more about this in It asks before it tells.

Where else your child will see convection

Once the loop makes sense, it shows up everywhere:

• Sea breeze. During the day, land heats up faster than the sea. Warm air over the land rises, and cooler air from the sea moves in to take its place.
• Land breeze. At night, the land cools faster, and the flow turns around.
• A room heater. Warm air rises from the heater, spreads across the ceiling, cools and sinks on the far side of the room.
• Boiling rice or dal. Watch the grains rise in the middle and sink at the sides.

Try it at home (with an adult)

You can see convection in your kitchen.

1. Put a pan of water on low heat.
2. Drop in a few tea leaves, or a pinch of sawdust.
3. Watch closely as the water warms. The bits rise above the heat, move across the top, and sink at the sides.

Ask your child to point to where the water is rising and where it is sinking, and to explain why. If they can, they have understood convection, not just memorised the word.

In short

• Hot water is less dense, so it rises. Cool water is denser, so it sinks.
• The loop is a convection current, and the heat at the bottom keeps it going.
• The Tutor writes each line as it says it, then asks your child to explain.