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Where's the middle

How can you find the middle of a ruler or long rod without measuring?

What to do

  1. Balance the ruler or long rod on top of your two index fingers.
  2. Slowly slide one finger towards the other.
  3. As that finger slowly moves toward the other, gravity will pull the ruler down harder on that finger. As this occurs there will be more friction between the ruler and that finger and you will reach a point where the ruler won't slide.
  4. Now begin sliding the other finger inwards until the same effect occurs.
  5. Continue sliding one finger at a time until they eventually meet.
  6. Wow - your fingers have met in the middle!

How it works

The combined effects of gravity and friction will mean that your fingers will always meet at the centre of the ruler.

The science behind this experiment is gravity and friction.

Gravity is the invisible force that attracts objects towards the earth and each other.

Friction is the resistance felt when an object is moved in contact with another.