Experiment : Egg in the bottle
Here's a classic science experiment that is more than a hundred years old and is guaranteed to fool your friends. The original demonstration used a hard-boiled egg and a milk bottle.
WARNING: This experiment requires the help of an adult partner. Don't just pick any adult... try to find a smart one!
- A wide mouth juice bottle
- Hardboiled eggs
- Several strips of paper (2X6 inches)
- A few balloons
The classic version of this experiment used a glass milk bottle. If you can get your hands on one of these bottle, you'll be in science heaven!
The object of the challenge was to somehow get the whole egg into the bottle without harming the egg. Since old milk bottles are hard to come by, here’s a modern day version of the same experiment only this time we’re using a juice bottle and a water balloon! Your job is to get the balloon in the bottle, but don’t break the balloon, or you’ll be all wet.
- Carefully fill the balloon with water, so the balloon is about the size of a tennis ball, and tie if off. Make several balloons just in case the first one breaks!
- Rinse out the bottle to remove any leftover, sticky, slimy stuff that might be in the bottom. Before going any further, make sure that the water balloon is slightly larger than the mouth of the bottle.
- Here’s the challenge: Your job is to find a way to get the balloon into the bottle… without breaking it. How are you going to do it? It’s important that you take a minute to test out some of your ideas before jumping ahead to read our solution. Keep trying!
Once you get the balloon in the bottle, how are you going to get it back out? Here's our answer!
- Start by smearing some water around the mouth of the bottle.
- Have the adult light a match and set the strip of paper on fire. Quickly put the burning strip into the bottle. Be careful not to accidentally burn your fingers.
- Immediately cover the mouth of the bottle with the balloon. In just seconds, the balloon will start to wiggle around on the top of the bottle, the fire will go out, and some invisible force will literally “push” the balloon into the bottle. That’s amazing!
Try it with an egg!
Just repeat the steps above substituting a hardboiled egg for the water balloon. The trick here is to find an egg that is just a little bigger than the mouth of the bottle - I prefer medium size eggs. The other little secret is to grease the mouth of the bottle with a vegetable oil so the egg slides right in!
How does it work?
The burning piece of paper heats the molecules of air in the bottle and causes the molecules to move far away from each other. Some of the heated molecules actually escape out past the water balloon that is resting on the mouth of the bottle (that’s why the balloon wiggles on top of the bottle). When the flame goes out, the molecules of air in the bottle cool down and move closer together. This is what scientists refer to as a “partial vacuum “. Normally the air outside the bottle would come rushing in to fill the bottle. However, that darn water balloon is in the way! The “push” or pressure of the air molecules outside the bottle is so great that it literally pushes the balloon into the bottle.
Remember this: When molecules of air heat up, they move far away from each other and take up more space. When molecules of air cool down, they move closer together and take up less space. Now, the challenge is to get the balloon out of the bottle. Use what you have learned about air and air pressure to come up with a way to get the balloon back out. Hint: Try sneaking a straw along side the balloon when you pull it out. If the outside air can get inside the bottle, the water balloon will come out!