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Home » Science Experiments for Kids » Chemistry » Convection Currents Made Easy

Convection Currents Made Easy

Modified: Aug 25, 2024 · Published: Jun 13, 2022 by Emma Vanstone · This post may contain affiliate links · Leave a Comment

When part of a liquid or gas is heated, it expands and becomes less dense. The warmer, less dense liquid rises upwards, and the cooler liquid falls to take its place. This cycle of a liquid or gas rising and falling is called a convection current.

We set up a very simple convection current demonstration using hot and cold water with food colouring to show the movement of warm water through cold water.

Convection Current Demonstration

You’ll need

Tall glass or vase

A smaller glass or cup

Hot water

Cold water

Food colouring

Warm coloured water in a small container in a larger jar of cold water to show warm water rises and demonstrate convection currents.

Instructions

Fill the tall glass or jar with cold water.

Fill the smaller container with hot ( but not boiling water ) and add a few drops of food colouring.

Carefully place the small container into the container with the cold water.

Watch what happens to the warmer, coloured water.

A jar of cold water with a smaller jar or warm water inside for a convection current demonstration
Second in a series of convection current demonstrations showing warm red water rising up through cold water
convection current science demonstration

The hot, coloured water rises upwards and collects at the top of the cold water. It then cools and sinks downwards. Eventually, all the water will be at the same temperature.

How does convection work?

Particles of warm water move more quickly and spread out. They rise upwards through denser, cooler water, which sinks to the bottom, where it warms up. Eventually, all the liquid is at the same temperature.

Warm water rises because when liquids and gases are heated, they expand. This means they take up more room but have the same mass, so their density is less than when they are cool. Substances with lower densities float on substances with higher densities.

Diagram showing water heating in a pan and the direction of heating. Warmer water rises, cooler water falls to take its place. This cooler water is then heated and rises.
Convection current in heated water

A hot air balloon is another example of convection currents in action.

Ask an adult to help with this activity

Extra Challenge

Repeat the activity with cold water instead of hot and watch what happens to the coloured water.

cold water in cold water for a science experiment about convection currents

You can see that the cold water isn’t moving upwards like the warm water.

How is heat transferred?

Heat can be transferred in three different ways.

  • Conduction.
  • Convection
  • Radiation.

Convection

Heat convection occurs when warmer molecules of a liquid or gas move from a warmer to a cooler area, taking the heat with them.

Water being heated in a pan is an example of convection. This is the type of heat transfer we demonstrated above.

Another way to demonstrate convection is with a spinning convection snake.

Conduction

Conduction of heat occurs when vibrating particles pass any extra vibrational energy to nearby particles. The more energy the particles have, the hotter the object gets. An example of this type of heat transfer is when metal pans are heated on a hob. Heat travels through the pan. If the pan handle is also metal, it will get hot, too. This is why metal pans often have plastic or wooden coverings on their handles. Plastic and wood are not good conductors of heat.

Radiation

Radiation of heat is when heat is radiated to the surrounding area by heat waves. Particles are not involved in this kind of heat transfer.

The heat from the sun travelling through space is an example of heat transfer by radiation. Waves transfer this type of heat.

Diagram showing convection, conduction and radiation with the example of a camp fire
Diagram showing conduction, convection and conduction

The campfire and pan example above shows all three kinds of heat transfer.

Heat travels by radiation from the campfire to the metal pan. Heat travels through the pan’s metal by conduction to warm the lower layers of water. The water is then heated by convection as the less dense warmer water rises through the cooler water, creating a convection current!

Remember – heat is only transferred if there is a temperature difference.

Science concepts

  • Density
  • Conduction
  • Convection
  • Radiation
  • Heat transfer
An image of red warm water rising through cold water and blue coloured cold water not rising through cold water for a convection current science activity

Last Updated on August 25, 2024 by Emma Vanstone

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Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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