The Reversing Arrow Trick
How we did it:
- clear cup
- dollar bill
- paper - with two arrows drawn on
1. Prop up your paper and set a clear glass in front of the arrows on the bottom of the page.
2. Look through the glass at the arrows. Which way do they go?
3. Keep watching the arrows and slowly pour water into the glass. The arrows change direction!
What's going on?
The water isn't really magic, of course, so how does the arrow change direction? You're seeing an optical illusion – in other words, something that isn't really there. In this case, the light from the arrow has to travel through the water to reach your eye. The water in the glass bends the light in such a way that the arrow seems to be pointing the other way.