What is the reversal of the arrow

The twisted arrow

Everything you need for this experiment:

  • 1 blank sheet of paper
  • 1 glass jug or 1 drinking glass
  • 1 jug of water
  • 1 felt pen

That's how it works:

1. Fold the piece of paper in half so that you can put it down like a place card.

If you bend your feet into the card, it will look better.

2. Draw an arrow on one side of the card that points from left to right (also goes from right to left).

3. Place the folded sheet of paper on the table and the glass jug or drinking glass about an arm's length in front of it.

4. If you look through the glass at the arrow, you can see it.

5. Now fill the glass with water.

6. Look again through the glass with the water at the arrow.

When light breaks ...

No magic: at the transition from glass to water, the rays of light are refracted in such a way that they arrive exactly the other way around in your eye. You think the arrow has turned. When two substances meet, rays of light are refracted. The decisive factor is how dense the materials are: in less dense materials such as water, the light moves faster, in denser materials such as glass it moves more slowly. In the empty glass, the glass walls hardly deflect the light. The arrow points in the original direction for the eyes.

The water in the full glass causes light to refract: the light is deflected. The rays of the arrowhead and the end of the arrow cross each other and arrive the other way round in the eye. So the glass acts like an erecting lens.

A similar principle is running in your eyes at this very second: If we see an object, this image arrives upside down on the retina of our eye: We still see the image upright because our brain turns it around for us.

What is happening:

The arrow has completely turned and is now pointing in the opposite direction! (If that doesn't work right away, change the distance between the glass and the arrow on the paper.)

More information at: Klaus Gruber | dolphin photography