What’s happening?

At first, waves seem like fairly simple things to understand. Go to the beach, and you’ll see plenty of them. A flag can wave in the wind, your hand can wave goodbye and even the air can ripple in waves, producing sound. But not all waves are the same. How does light move as a wave? Is a wave at the beach the same as a sound wave?
This simple wave machine demonstrates how energy can move through something and form a pattern of movements. Each skewer is joined to the next by a section of tape; by pushing down one end of a skewer, you twist the tape. It springs back again, pulling the skewer back so it shoots up, now twisting the tape in the opposite direction. Meanwhile, the tape is also tugging on the next skewer, making it wobble. Energy transfers down the tape, making each skewer see-saw up and down, creating a wave.
Waves at the beach are similar to this movement, where the water seems to move in a particular direction. We call them transverse waves, because the water goes up and down while the wave moves forward. Sound waves, on the other hand, wiggle back and forth in the direction they are heading, and are described instead as ‘longitudinal’ waves.

Applications

If you’re a surfer, you can use the waves on the ocean to push you along. But the water isn’t really flowing anywhere. Watch a seagull sit on the surface – like the water, it stays in one place as the wave makes it bob up and down.
These waves are caused by the wind blowing on the surface far out at sea. A combination of the water’s own friction, gravity and the moving air make the particles on the water’s surface roll down into the water and back up again in a circle. This pushes on more particles deeper down, making them move in a slightly smaller circle as well, and so on down into the depths. The circular motions of the water particles are like the skewers bobbing up and down and tugging on their neighbours.
As this wave reaches the shore, the ocean gets shallow, flattening the circles and pushing them together and changing the wave’s shape until it tumbles over itself and crashes. Like the marshmallows, the water doesn’t really go anywhere even though the wave moves forward.
Tsunamis aren’t like the transverse type, wind-driven waves, but are pushed by a sudden drop in the ocean floor, usually caused by an underwater earthquake or volcano. The water’s particles are jiggling back-and-forth as a longitudinal wave, similar to a sound wave, creating a wall of water that surges onto the land rather than one that curls gracefully like the perfect surf.

You will need

• Packing or cloth tape
• 20 wooden skewers
• 40 marshmallows
• 2 chairs

What to do

1. Unroll just over 1m of packing tape and lay it on a surface sticky-side up.
2. Carefully arrange your twenty wooden skewers perpendicular (across) the tape, leaving a gap of 5cm between each of them.
3. Unroll another metre of packing tape and lay it sticky-side down on the first strip, sandwiching the skewers between the two.
4. Push a marshmallow on both ends of each skewer.
5. Facing them back-to-back, separate the two chairs enough to stretch the tape between them.
6. Use more packing tape to secure each end of the strip of skewers to the backs of the chairs.
7. Tap a marshmallow at one end and watch the wave ripple down the tape.
   

   	Unroll a metre of tape
   	Arrange the skewers with a gap of about 5cm.
   	Stick marshmallows on each end.
   	Make waves!