The Atmosphere in a Cake Tin - Lab activity
In this activity we will model the air movements that occur when air is cold in one place (for example, at the
poles) and hot in another (for example, the equator). We will use water to represent air in the lower part of
the atmosphere (troposphere) because it’s easier to observe the motion of water than it is to observe the
motion of air.
Part of Model
Bottom of tin
Real thing it represents
The Earth’s surface
Water in the tin
Air above the tin
Higher level of the atmosphere / space
Bag of ice
Cold ground near the north or south pole
Candles
1. Complete the table below to explain what each part of the model represents
Materials:
Large cake tin
Red and blue food colouring
3 small candles
matches or lighter
3 cups or beakers
Ice inside a bag
Red and blue coloured pencils
Instructions:
1. Fill the cake tin with water
2. Place the three cups or beakers upside down on the table, forming a triangle that the cake tin can
rest on. Place the cake tin on the three cups
3. Light the candles and place them in a line underneath one end of the cake tin. Which region of
earth does this represent?
__________________________________
4. Place the bag of ice on the side opposite the candles. Which region of earth does this represent?
__________________________________
This is what your model should look like:
Questions:
1. On the diagram on the previous page, use arrows to show any (invisible) motion of the water that you
think may be occurring due to temperature differences across the cake tin.
2. Explain why you think the water is moving this way.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
Instructions continued:
5. After the cake tin has rested undisturbed for 5 minutes, place several drops of blue food colouring
in a line along the bag of ice, near where it touches the water (see diagram below)
6. Carefully place several drops of red food colouring in a line along the BOTTOM of the cake pan
directly above the candles (see diagram below)
7. Watch the motion of the coloured water and answer the following questions.
Questions continued:
3. On the diagram below, use arrows and coloured pencils to show the motion of the red and blue water in
the cake pan.
4. Did the motion you observed match your predictions? If note, explain why the motion that you did
observe occurred.
_______________________________________________________________________________________
_______________________________________________________________________________________
5. What can we conclude about the density of the water near the candle as compared to the density of the
water near the ice? Where is the water more dense? Why?
_______________________________________________________________________________________
_______________________________________________________________________________________
6. Are there any inaccuracies in your model? Describe them and suggest how they could be overcome.
_______________________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________
7. Which of the three types of heat transfer are occurring in your model? Explain where they are happening
in the model.