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Hot hot heat

By Jasmine, 19 December 2012 Activity

Two closed cardboard boxes.

Find a sunny spot for your boxes.

Phew! The Sun can feel pretty hot, even though we’re millions of kilometres away on Earth. Find out more about how plants can keep buildings cool in this activity.

outdoor hazard iconSafety: This activity requires you to head outdoors. Ask an adult for permission, and make sure they know where you are. Protect yourself from the sun by wearing a hat, shirt, sunglasses and sunscreen.

You will need

  • Pot plant
  • 2 identical cardboard boxes
  • 2 thermometers
Hand placing a thermometer into a cardboard box.

Put a thermometer inside each box.

What to do

  1. Take your equipment outside and find a sunny spot.
  2. Position your boxes in direct sunlight (no shade). Make sure the boxes are far enough apart that they do not cast a shadow on each other.
  3. Place a thermometer inside each box.
  4. Position the pot plant so it is casting shade over one of the boxes.
  5. Wait 15 minutes.

    A cardboard box obscured by a pot plant.

    Shade one box using a pot plant. What is the temperature difference between the two boxes after 15 minutes?

  6. Read the temperatures off the thermometers inside the boxes. What effect did the plant have?

What’s happening?

The Sun radiates heat and light energy. The boxes capture heat from the Sun trapping it inside. The air trapped inside the box is a very good insulator; it doesn’t allow the heat to escape. This is why the air inside a car gets very hot on a sunny day too.

A pot plant creates shade. It can stop sunlight reaching the box, helping to keep the box cooler. Some sunlight bounces off plants as heat or reflected light. Green plants also absorb some sunlight to produce sugar in a process called photosynthesis. This gives them the energy to grow and survive.

Plants also transpire, giving off water which then evaporates. This can have an additional cooling effect.

Real-life science

In summer, a tree with leaves can shade your home, decreasing the amount of sunlight striking the house, keeping it cooler. If you choose a deciduous tree, it will drop its leaves in winter allowing sunlight to reach the house, keeping it warmer.

If you choose suitable plants, they could reduce your need for air-conditioning in summer and heating in winter. This reduces energy bills and is good for the environment too.

When planting trees or plants around your home, think carefully about which types you choose. A few things to consider:

  • Latticework with vines can be used if you don’t have space for trees or shrubs.
  • Know the final height and width of the trees – you don’t want them growing too big, or too close to your home.
  • Make sure you choose plants that aren’t too thirsty. With water restrictions it might be difficult to keep some plants green and leafy.
  • Don’t plant trees near power lines.
  • Don’t plant trees too close to the house or branches can drop on your roof during storms.

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