Two-Winged Fruits
Students’ Sheet
Introduction
One-winged fruits are the most common, but
some fruits have two wings. Both types are
sometimes called helicopter fruits because of
the way they spin as the fall downwards.
The Karanjali tree grows up to 45 metres tall.
Its trunk is straight and can be 1.50 m in
diameter. It is sometimes used to make dug-out
canoes. It is an endangered species.
In this activity you will investigate the flight of
two-winged fruits.
A two-winged fruit of the Karanjali tree
(Dipterocarpus bourdillonii)
Activities
Activity 1: Modelling a two-winged fruit
Model 1
You will need two strips of paper, each 1.5 cm x 10 cm, for the wings and a paper clip for the
seed. If you want to time the flight of your model you will also need a stopwatch.
Use your thumb and forefinger to curl the two ‘wings’, starting about 3 cm from the bottom of each
strip. Hold them together at the uncurled ends and with the wings spread in opposite directions.
Attach a paper clip to hold them together.
top 7 cm curled over
bottom 3 cm
not curled
paper clip – you need
to experiment to find
its best position
You can see the similarities between it and, for example, the fruit of a Karanjali tree.
Now try it out. You may need to make some small adjustments such as how far the paper clip is
pushed on and ‘curl’ on the wings.
Science & Plants for Schools: www.saps.org.uk
Two-Winged Fruits: p. 1
Model 2
You will need a strip of paper 3 cm x 10 cm, scissors, a pencil, a ruler and a paper clip. If you
want to time the flight of your model you will also need a stopwatch.
Cut the 3 cm x 10 cm piece of paper as shown in the diagram on the next page.
3 cm
8 cm
10 cm
Cut along these
three line and
discard the two
triangular
pieces of paper
1 cm
1 cm
Use your thumb and forefinger to curl the two ‘wings’ in
equal but opposite directions.
Attach a paper clip to the tapered end. The picture on
the right shows what you are aiming for. You can see the
similarities between it and, for example, the fruit of a
Karanjali tree.
Now try it out.
As with model 1, you may need to make some small
adjustments such as how far the paper clip is pushed on
and ‘curl’ on the wings.
Questions
For each of the models:
1. Describe where the centre of mass is for the model fruit.
2. Describe the movement of the model fruit as it falls to ground.
3. Explain how the movement relates to the centre of mass.
4. Suggest reasons why the model moves as it does.
Note: The aerodynamics of flight are complicated, so don’t expect to be able to give a ‘right’
answer. Just think about gravity and about the arrangements and movement of particles in solids
and gases.
Science & Plants for Schools: www.saps.org.uk
Two-Winged Fruits: p. 2
Activity 2: Investigating the design of your model winged fruits
Although the model you made is simple, you can vary its design and find out how the changes
affect the flight of the model.
If there is time explore the effects of changing one of more of these design variables.
1. The length of the paper.
2. The width of the paper.
3. The thickness of the paper, e.g compare models made from paper and card.
4. The mass of the paper clip (perhaps by adding small pieces of plasticine).
It’s up to you to decide what to investigate.
Working in a small group, write out your plan and check it with your teacher.
Remember: Only change one variable at a time. If you make two or more changes you won’t
know what did what!
Question
What conclusions did you draw from the results of your experiments?
Science & Plants for Schools: www.saps.org.uk
Two-Winged Fruits: p. 3