Convection in Action: Witness how temperature drives convection

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Convection is how a liquid or gas moves due to temperature, and it’s everywhere from the boiling water on a stovetop to the massive clouds you see in the sky. Actually seeing convection in action can be challenging though. But I’ve got an experiment to help with that!

This experiment demonstrates convection in action by heating a container and watching the liquid inside of it rise and sink. It showcases the importance of temperature in convection, as well as how temperature can affect the density of a liquid.



How to make the Convection in Action STEM experiment

Supplies you will need

For this experiment, you’ll need:

Supplies needed for the Convection in Action STEM experiment

Before you start

Please watch fingers around the open flame.

Instructions

Here is how to do this experiment with your child:

Step 1: Pour oil into glass

Pour the cooking oil into the glass container. We added enough to almost fill up the glass container.

Pour the oil into the glass container

Step 2: Prop up the glass onto blocks

Use two small blocks to prop up the glass container. The blocks need to be small enough that the flame from the tealight candle can almost reach the bottom of the container.

We used a couple of the Melissa and Doug wooden blocks. They were the perfect height!

Place the container on blocks

Step 3: Place candle below glass and light

Place your tealight candle between the two blocks and be sure that it will hit right around the middle of the container.

Light the candle and replace the container on the blocks.

Place the tealight candle between the blocks
Light the tealight candle

Step 4: Add drops of food coloring to the oil

Add some drops of food coloring to the container of oil. The food coloring drops will start to glob together, so use a knife to stir it occasionally (especially when the oil has been heated).

Add food coloring drops to the oil
Video showing the food coloring drops moving around in the oil

The STEM behind the Convection in Action experiment

This experiment teaches:

  • Convection
  • Density
  • Temperature

How it works

This experiment demonstrates convection, density, and temperature by heating a glass container of oil from beneath and adding food coloring drops to see the convection in action.

When the glass container is heated from below, there is a temperature difference between the bottom of the glass and the top. The warmer, less dense oil at the bottom of the glass rises. The cooler, more dense oil at the top of the glass sinks. The food coloring drops allow us to see the motion of rising and sinking oil.

This experiment helps kids to learn that temperature is the driving force behind convection and can also play a big part in the density of a liquid.

Convection

Convection is the process of heat transfer that occurs through the movement of fluids, such as liquids and gases.

When we heat up the oil inside of the container, the molecules in the liquid start to gain kinetic energy and move around faster, spreading out. When the molecules spread out like that, the oil starts to become less dense.

That less dense, warmer oil then becomes “lighter” than the surrounding cooler, more dense oil, making the warmer oil rise. As it rises and moves away from the candle beneath the glass, it starts to cool down, making it more dense and sink.

This motion creates a cycle, with warmer oil rising and cooler oil sinking in a big circle. That’s convection!

Density

When we place the glass container of oil over a candle and the oil inside of the container begins to heat up, the oil in closest contact with the heat source becomes less dense.

Why does that happen?

The oil is increasing in temperature, which increases the kinetic energy of those molecules closest to the flame. The increase in kinetic energy causes the molecules to “jump around” more, making them spread out. That’s the decrease in density that we see near the flame!

The oil at the top of the container, which is still cooler, has a higher density than the oil closest to the flame (remember, due to kinetic energy, or lack of it).

That’s why the oil at the top of the container sinks and the oil at the bottom rises.

It works the same for hot air balloons: the hot air inside of the balloon is less dense than the cooler air outside, which causes the balloon to rise.

Temperature

Temperature is the big driving force in this experiment. Convection itself is started and continued because of temperature differences within the oil.

Density is also affected by the temperature because when it is heated, it expands and becomes less dense. When the oil is cooled, it becomes more dense than the oil below it.

In short, if there is no temperature difference, there would be no density differences or convection in our glass container, and no experiment!



More experiments about density and convection to try out with your child

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