It’s not what you think

Iam always looking for fun and quick activities to do when I am able to visit all the young scientists in the classroom. They help me show the Scientific Method and how this is applied to the experiments that we are doing. This activity is particularly interesting as it does not do what many of them hypothesize. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

• 2 empty pop cans

• 24 drinking straws

• Ruler

• Table to work at

Procedure:

1. Using a ruler, lay out all but one of the straws one centimetre apart and parallel to one another.

2. Place the two empty cans in the middle of the straws (standing up). Move them about five centimetres apart from one another trying to keep them as close to the middle of all the straws as you can.

3. Make a hypothesis — what do you think will happen and why?

4. Using the remaining straw, blow a steady stream of air BETWEEN the two empty cans.

5. Observe.

6. Was your hypothesis proven or disproven?

What is going on?

Most people will expect the cans to roll apart from each other. You would have observed that the cans actually roll towards each other. Hmmm... this is due to a special scientific principal know as Bernoulli’s Principle.

The Bernoulli Principle states that the pressure of a liquid decreases as its velocity increases. With our experiment here that means that as you blow a steady stream of air between the two empty cans, the velocity of the air between the two cans increases, and the pressure that the air is applying to the inner sides of the cans decreases.

That allows the air on the opposing sides of the cans to push the cans towards to the area of lower pressure. We didn’t in anyway increase the air pressure on the outside of the cans so the cans were not “sucked” together, rather it was the decrease in pressure between the cans that allowed the cans to roll towards each other, they were pushed together!

We are still in need of some science fair judges so if you would like to lend a helping hand, send me a message!

Patty Rooks, Senior Scientific Consultant PRAXIS, “Connecting Science To The Community”. Contact Praxis at praxis@praxismh.ca, www. praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook. Address: #12 826 11 Street S. E., Medicine Hat, Alberta, T1A 1T7 Phone: 403.527.5365, email: praxis@praxismh.ca.