Is this magic or cohesion at play?

I thought today would never get here. Halloween has finally arrived. I absolutely love this day.

Many people ask me to share the wonders of science on this day in particular as often times it looks like

“magic” when we do science experiments.

I was very fortunate this year to be invited to the Esplanade’s Halloween Extravaganza to share this mysterious world of science. There will only be three shows today, so do not forget to get your ticket online before heading down and enjoying an exciting time learning about science.

If you cannot make it, here is a sneak peek at one of the activities we may be doing – warning – someone may get wet. Let’s get started.

Remember to ask an adult before doing this experiment.

Materials

500 mL mason jar with an outer sealing band (the canning type of li)

pitcher or clear container full of water mesh screen index or playing card scissors willing participant!

Procedure

1. You must prepare ahead of time as you do not want to reveal the magic secrets before you do this activity.

2. Remove the lid from the jar.

3. Place the mesh screen over the opening to the jar and hold it in place with one hand while trimming it with the scissors. You want it to fit entirely over the opening to the jar.

4. Carefully place the outer sealing band back on the jar.

5. Now you are ready for an audience.

6. Have your willing participant sit down in a chair. You want the be able to hold the jar over their head.

7. Take the pitcher full of water and fill the mason jar (you prepared ahead of time) with water. Do not worry about anyone seeing the mesh in there. They will likely not even be looking.

8. Place the card over the opening of the jar. Push it firmly in place and holding it there, and turn the jar upside down (over top of your volunteer)

9. Hold it there for a minute.

10. Carefully and slowly slide the card out from the jar.

11. What happens?

What is going on?

If you did this correctly, your volunteer should not have got drenched. The water should have stayed in the jar when you removed the card slowly. How can that be?? Water should come pouring out. Not in this activity and you guessed it, due to science.

There are several scientific principles present in this activity. The first is atmospheric pressure. This is the pressure that holds the card in place when you flip the jar upside down. The pressure of the air molecules pushing up on the card are actually greater than the pressure of the water pushing down on the card.

The water would not stay in the jar if it was not for surface tension. As I have mentioned before water is an amazing substance and it is almost like it has this thin skin on the top of it making it do amazing things. Be extra careful when doing this experiment, as if you tip the jar at all, someone is bound to get wet. This is because you will break the seal or the surface tension of the water.

Cohesion is the last scientific principle at play here. Thankfully the water does not go all over your volunteer because of this. The water does not come rushing out because the molecules of water are held together by cohesion.

I hope to see you soon.

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.