Gliding is one way that the fruits and seeds of some plants have adapted and evolved to improve their dispersal. The Javan cucumber (Alsomitra macrocarpa) is a wonderful example of a plant that produces fruit that releases seeds capable of gliding vast distances. The plant grows in the forests of Java, Indonesia. The fruits are about the size of a football and each is packed with hundreds of winged seeds. The seeds fall from the underside of the fruit and glide vast distances.
For information: A Javan cucumber seed has a mass of 0.3 g, a transparent wing with a span of 15 cm, and a wing thickness of less than 0.01 mm (less than 1/10th the thickness of a sheet of paper).
Other winged fruits and seeds rotate as they fall. Typically they descend at about 100 cm each second. But the design of the Javan cucumber seed means that it descends at the shallow angle of 12 degrees and falls only 40 cm each second.
The seed inspired early aircraft wing design and its aerodynamic properties have been researched.
The activities in this sheet could be used alongside any of the other sheets in Seed dispersal.
Possible barriers to learning
The session allows a number of common misconceptions associated with gravity and objects falling to Earth. Depending on the nature of discussions with students, misconceptions that could be addressed include:
something stops moving because the force has run out
air doesn’t weigh anything
particles are the same as visible grains as in rocks, for example.
Links to National curriculum for science in England at key stage 3
In biology pupils should be taught about reproduction, which includes:
reproduction in plants, including flower structure, wind and insect pollination, fertilisation, seed and fruit formation and dispersal, including quantitative investigation of some dispersal mechanisms
In physics pupils should be taught about forces, pressure in fluids and forcers and motion. This includes:
access to the Internet (this part – watching videos – could be done at home)
3 or 4 sheets of A4 paper
pencil and ruler
optional: stopwatch or other timer if descents are to be timed
Activity 1: Watching them glide
The video is remarkable. You may well want to watch it, talk about it with the students and then watch again to reinforce or look for answers to questions that students may have raised.
Answers to questions
1. (a) the main features are the position of the seed and the shape of the wing, (b) it glides gracefully and slowly.
2. The wing decomposes and the seed germinates.
3. Student might just estimate it given the position of the seed. The centre of mass for any irregular shaped object can be found by hanging it from various points so that it can swing freely. A piece of string with a weight attached to one end is hung from the same suspension point. Using the string as a guide, a vertical line is drawn. This is repeated for one or two other suspension positions. The point where the vertical lines cross is the centre of mass.
If time allows, students could do this with the origami model they make in part 3.
Activity 2: Investigating aerodynamics
This very simple investigation shows how a rectangular piece of paper that spins slowly to the ground can be transformed in a glider. The dimensions are not critical, but the ones given should ensure that the glider ‘works’. However, variations have been tried on smaller and larger models and with the thickness of the leading edge (by making more folds).
So students might experiment to see who can make the ‘best’ glider (of course, they will need to decide what ‘best’ means – longest flight, smoothest flight and so on).
1. X spins; Y with folds on top turns around and begins to glide in the opposite direction; Y with the folds beneath glides smoothly.
2. X has two, but Y only has one
Paper strip X
Paper strip Y
3. Centre of mass of strip X is where lines of reflective symmetry cross; centre of mass of strip Y is on its line of reflective symmetry, but closer to the leading edge.
4. They need a leading edge, which gives a centre of mass nearer to the front of the glider
5. Any explanation in terms of pushing air particles out of the way as the glider moves through and the effect a leading edge has on this. The forces that act on the object are (a) gravity, pulling the object to Earth, (b) air resistance (sometimes called upthrust).
Activity 3: An origami Javan cucumber seed
This is not too difficult to make, but it does require care. The trickiest bit is making the two folds in step 3, as explained in the students’ sheet.
The dimensions suggested give a model fruit that has the same wing span as a Javan cucumber seed.