What it shows
A disturbance can travel along a line of objects without the objects moving along. The machine shows a transverse wave with crest, trough, wavelength and speed.
The science
In a transverse wave, particles move up and down while the wave moves sideways. The wave carries energy, not matter. The distance between two crests is the wavelength, and wave speed equals frequency times wavelength. The weights make each rod swing slowly so the wave can be seen. The tape twists as the rod moves and passes the motion on to the next rod.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- About 40 bamboo skewers or drinking straws
- Strong double-sided tape or long clear tape
- Jelly beans or clay balls for weights
- A table edge or a stand
- A ruler and a stopwatch
- A marker
Safety
For this project: An adult must trim the sharp tips of the skewers and cover them with clay.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Stick a long strip of tape, sticky side up, on a table.
Place the skewers across the tape at 2 cm spacing.
Press a second strip of tape on top to hold them in place.
Add a clay ball at each end of the skewers.
Lift the tape machine by the ends and hold it between two chairs or books.
Flick the end skewer and watch the wave travel along.
Measure the time for the wave to travel the length and calculate its speed.
Mark crests, troughs and a wavelength on a drawing.
What you should see
A visible wave travelling the length of the machine and reflecting at the far end.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a transverse wave?
A wave in which particles move at right angles to its direction.
2What does a wave carry?
Energy, not matter.
3What is wavelength?
The distance between two crests.
4What is the formula for wave speed?
Speed equals frequency times wavelength.
Take it further
Change the weights and see how the wave speed changes.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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