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Did you know you can control the speed of a splash? Time to make some speedy waves, before using a neat trick to slow them down.

You will need

• Clear bottle with lid
• Water
• Food colouring
• Vegetable oil
• Funnel
• Paper towel (to clean spills)

What to do

1. Half fill the bottle with water, add some food colouring and screw on the lid.
2. Tilt the bottle on its side and create waves by moving the bottle back and forth. Watch the waves.
3. Put the bottle upright, take the lid off and put the funnel in the bottle’s mouth. Keep the coloured water in the bottle.
4. Fill the bottle with oil. Take the funnel out and carefully top up the bottle so the oil goes right to the brim.
5. Screw on the lid. Then clean up any spills with paper towel!
6. Tilt the bottle on its side and wave it back and forth. Watch the waves in the bottle. What’s different this time?

What’s happening?

Water splashes around quickly in a half full bottle. But top it up with oil and the waves chill to a much more sedate pace. So what’s going on?

In this activity, the waves are made of water, but water isn’t the only thing moving in your bottle. As water flows into a space, the stuff that was there must get out of the way. Air is light and easy to move, but oil is almost as dense as water – so it takes a lot more effort to push the oil out of the way!

Slowness isn’t the only cool thing about the waves in the full bottle. Things can look very weird in there! When light travels through different materials, it gets bent at an angle. When the material is curved, like the sides of a bottle or the surface of a wave, it can act as a magnifying lens. Sometimes light gets bent so far it reflects instead, making the surface look shiny!

If you’re after more science activities for kids, subscribe to Double Helix magazine!