Transverse waves along a rope
Introduce the concept of a transverse wave by drawing attention to a wave pulse as a displacement at right angles to the direction of travel along a rope.
Apparatus and materials
For each student pair
length of flexible rope (the longer the rope the better, minimum length 3 metres). The rope should be a massive, loose rope - not a stiff one.
Health & Safety and Technical notes
A lot of space is needed for students to demonstrate waves along ropes. If the whole class is to do this at one time, arrange to use a long, wide corridor or the school hall.
Students work in pairs, each holding one end of the rope in mid-air. One tries to hold the rope still. The other uses a hand to jerk one end of the rope up and quickly down, stopped on the wrist of his/her other hand.
Alternatively, this could be done on a bench or on the floor.
If the rope is held in mid-air, pulses are likely to reflect back and forth several times.
1 Draw students’ attention to the way that the pulse diminishes in size as it moves along the rope. You may also want them to observe the inversion of the pulse after each reflection.
2 Challenge the student holding the far end of the rope not to let their hand move. That they cannot do so always surprises and intrigues them - and makes it clear that energy is being delivered.
3 Students may produce both continuous waves and standing waves without further instruction.
4 To produce standing waves: mark off the rope into equal segments, such as fifths. Holding the ends of the rope tightly, each person makes a loose ring with a finger and thumb round the rope at the nearest marked point. One person then moves the rope up and down, adjusting the frequency until the 5-loop motion builds up. Different resonances can be produced, of course, by changing the frequency of the tension. This impedance matching will produce an effective standing wave.
5 Alternatively this video, from the National STEM Centre eLibrary, shows how to model transverse waves using a wave machine which is simple to construct.
This experiment was safety-checked in February 2006