Monday, June 23, 2014

Can Crusher

This is a very impressive activity and can really surprise people and make them jump. They will want you to do it again and again, so bring extra supplies.


What they will see: The presenter puts a small amount of water in a soft drink can and then picks it up with  a  pair of tongs. The can is held over a flame until a sizzling sound is heard and steam is seen leaving the can. At just the right moment, the can is plunged head first into the water, where it violently implodes with a loud pop! When the can is pulled out of the water, it is seen to be extremely flattened and crumpled, and all in a split second.

What You Will Need:
*Heat source: I use a 1 burner gas burner that screws on top of a small propane bottle. I tried a blow torch once, but I burned a hole in a couple of cans. You'll need enough heat to boil a small amount of water quickly in the aluminum can. Electric heat is too slow and needs direct contact. Have an extra propane bottle, just in case.

*Lighter for the burner: I like those sparkers that welders use, but any reliable fire source will do.

*Aluminum soft drink cans. I use about 5 or 6 cans when I do this. One will not be enough because everyone will be surprised by what happens and want to see it again.

*A large bowl or pot full of water: The experiment doesn't require a lot of water, but it is easier to see what happens if the bowl or pot is full. All the action happens near the surface, and if the bowl is only half full, the effect may be obscured to those sitting further away.

*BBQ or salad tongs: They should open big enough to hold a can. Shorter ones may get your hand closer to the heat source, while longer ones can be clumsy.

*1 Teaspoon measuring spoon: 

*Something to say: A little humorous dialog,  a story line and some showmanship will make it all a lot better.

How to do the experiment.
Before you begin, check for safety. Make sure people stand back and don't rest their weight on the table and upset the water or collapse the table or get close to the flame. Have a mop and some paper towels in case of spills. Safety googles may not be necessary, but they can add to the drama and anticipation of the experiment, so use them if you have them.

1. Have the water filled bowl ready to go. Have the bowl filled close to the brim with cold water, the colder, the better, but you don't have ice water.
2. Put a Tablespoon of water into the can.
3. Light the burner.
4. Pick up the can with the tongs. I like to hold the tongs with an underhand grip so that I can make one smooth move when it comes time to plunge the top of the can under water.
5. Hold the can over the flame. Position the can so that it is tilted a bit, so that the water pools well in the bottom of the can right over the flame. Flames sometimes burn through thin aluminum if no water is on the other side. Note where the hole is. With the can tilted a little to one side, the hole on the top side shold be on the lower edge, not the upper edge. This allows the steam to pool a bit as it rises before it leaves the can.
6. Listen and feel for the water boiling in the can. Watch the steam as it exits the top of the can. It will start slow and build up in speed and in volume. Wait a few moment until you see the steam begin to decrease and feel that the water in the can is almost all boiled away.
7. With one graceful arch of motion, move the can top first toward the water. The can should enter the water at close to a 90 degree angle, so that the water completely covers the top top of the can.You don't have to be violent or supper fast here, just make one smooth move and get that can top into the water without any hesitation.
8. The can will pop and maybe splash a little. Lift it out of the water and show everyone what happened. I like to shake it off a little and ask who wants to see it and then I toss it to them. Make sure it is not to hot and the age group and situation is appropriate before you do this.
9. Ask if they want to see it again. Try it with a different soft drink cans in different colors.
10. Tell your story, make your point or tell them the science behind the experiment.

Why It Works
When the water boils, it turns into steam and the steam pushes out the air. The pressure on the outside and the inside of the can is about 15 lbs of pressure per square inch at sea level. When the can is place upside down under water, the steam left inside condenses back into a few drops of water. Because the can top is under water, the air cannot rush back in to equalize the pressure. The pressure on the inside plunges to almost zero, while the pressure on the outside remains at 15 lbs or so per square inch. All that pressure flattens the can in a split second, just the same as if an elephant stomped on it.


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