I recently did a piece on measuring the speed of light using your microwave. Well here is some more physics you can play with in your kitchen. This time let’s create a vacuum and then use it to crush something. I like crushing things. Don’t we all?
What you will need:
- A regular drinks can
- A pot of cold water big enough to submerge the can
- A pair of tongs
- A kitchen hob (gas or electric is fine).
What to do:
Now you have to be careful with this one. The tongs have to be good or you’ll burn yourself. If you’re a child reading this, then make sure someone supervises you while doing this experiment. Reading though all the instructions before you start out is vital. I recommend having a couple of attempts, so maybe have two or three cans ready. So let’s begin:
Whilst you are filling up the pot of water why not drink the coke or whatever is in your drinks can. We don’t need any of the contents for this experiment, just an empty can. Once it is empty, rinse it out and place about two tablespoons of water in the can.
Now take your tongs and get a firm hold on the can. Hold it over the kitchen hob. We need to boil the small amount of water we have put in the can. This won’t take long and you’ll know when it’s worked because you’ll see steam coming out of the hole at the top of the can. Let it steam for a minute or two to be sure the water has all boiled.
Now here’s the cool bit. Keeping the can in between the tongs, take the can directly from the hob and dunk it, upside down, into the pot of water. The can will instantly and violently be crushed! It will happen very quickly so be ready. When I did it, it made a loud smacking sound as it went under water. I did it twice because I missed it the first time!
What is happening?
There is some great physics going on in this simple experiment. When you heat up the can and boil the water inside, the can fills with steam and pushes out all the air. Then when you dunk the can into cold water, the steam quickly condenses into water and there is no air pressure inside the can to support it. The can cannot resist the forces pushing on all sides from the water and air above it. Therefore it is crushed instantly!
Balloons:
Air pressure is also at work in balloons. When you blow air into a balloon you are artificially increasing the air pressure inside it and the rubber skin expands outward, forced by the force of the air molecules bounding around inside it.
You can ‘crush’ balloons by dipping them into liquid nitrogen. This condenses the air inside into a liquid and the balloon goes flat as a pancake. Here can see a video of a balloon that has been dunked into liquid nitrogen thawing out. The air boils back into a liquid and the balloon re-inflates. We filmed this last year in our first year undergrad physics lab.
[youtube]http://www.youtube.com/watch?v=HDjL7ON-2qE[/youtube]
Enjoy playing with air pressure and feel free to send me any images of your crushed cans!
It’s mostly atmospheric pressure that squashes the can, unless you propose plunging it to the bottom of the (more than 10 metres deep) sea.
Fun experiment, though! I’ll see if I can demo it to my kids with an electric hob.
Good point, well spotted. I was getting carried away. I have updated the post accordingly. Thanks.
We love experiments that involve food! Here’s my spin on your article
Camp cleanup with destructive science!
Cool!! I love these experiments!
Although this means I don’t get to crush it on my forehead, grunt and go “GRRRR”
Not that I do that…
…not often anyways.
Hi rob you should show the infra red heat camera thing it is very cool
HEYY THAT WAS COOL…
IM DOIN THAT FOR MY SCIENCE FAIR PROJECT
wow…cool…i’m doing a science thing for school and we are shaking different kinds of pop and see which one sprays better (coke, diet coke, pepsi, diet pepsi and Mt. Dew) me and my partner said coke because personal we think cke has more pressure…right???
Kristi,
I worked for Coca Cola for many years and thought I’d answer your question.
All soft drinks- Coke, Pepsi, whatever are made up of 1 part flavoring (syrup) and 5 parts carbonated water.
Except for the flavorings they are the same. One variation is the amount of caffeine they contain. Caffeine is a white powder that is added to the flavoring. As you may know, Mountain Dew and others contain more caffeine that the average drink. Some drinks are caffeine-free, but you might not know it. These include most Root Beers and clear drinks (7up).
Carbonated water is made by a simple machine called a carbonator. It consists of a chilled tank that is pressurized by CO2 (carbon dioxide- the same stuff you exhale). Cold water is sprayed into the tank of CO2 by a high-pressure pump. The CO2 goes into solution with the water and you have carbonated water. The CO2 will stay in solution as long as there is some pressure and the temperature stays around 34 degrees. Above that temp the CO2 expands and starts coming out of the water. Agitation will also shake the CO2 loose.
There are a lot of myths about Coke (which applies to all soft drinks).
1. Coke doesn’t remove rust well. The carbonic acid is too weak. However, over time the acid will eat through stainless steel. There is actually more acid in the flavorings, but still too weak for metal cleaning. Both really do a job on metal tooth fillings.
2. Carbonated water (soda water) doesn’t clean restaurant grills any better than plain water. The temperature difference and steam on a hot grill does the cleaning. Beside that CO2 disappears as soon as the temp goes up.
Now, to your point about more or less pressure, they are all the same because they all get the carbonated water from the same machine on the bottling line. When changing from one flavor or brand to another, the bottler changes the flavoring and cans then starts up the line again. All flavors get the same carbonated water and therefore contain the same potential pressure. Little to no pressure is generated by the flavorings.
This got a little longer than planned, but I hope it is of some use.