A flow of air into a venturi meter

Can we please lower the pressure in here?

Named after Daniel Bernoulli, the Bernoulli Principle states that as the velocity of a fluid increases, a decrease in pressure occurs. The mathematician Daniel discovered many new ideas regarding fluids and pressure. For instance, Bernoulli, who had earlier begun to study medicine, wanted to know about the relationship between the rate of blood flow and its pressure. He poked a hole in a pipe and stuck a straw in it and noticed that when the fluid sped up, the liquid rose higher in the straw. Soon doctors all over Europe were poking holes in patient’s arms and sticking little glass tubes in them to test their blood pressure. Ouch! This practice continued for nearly 200 years until an Italian doctor discovered our modern method of measuring blood pressure.

  1. Place 30 to 40 straws next to each other on a flat table. Leave about ½ inch space in between them.
  2. Place the two empty soda cans on the straws so that they can roll back and forth on the straws. Leave about 1 inch of space in between the cans.
  3. Take a straw and blow air through it in between the two cans.

You may have thought that by blowing air between the cans they would spread apart but the opposite actually happens – the cans move closer together. This happens because the velocity (or speed) of the air between the cans is increased when you blow between them with the straw. Bernoulli’s principle states that as the velocity increases, the pressure decreases. The lesser pressure in between the cans causes them to move towards each other.

Experiment Supplies

Supplies: Straw, Soft drink can


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