- A drawing pin (if you don’t have a drawing pin, you can use sharp scissors or a knife)
- A ballpoint pen
- 2 plastic bottles (each 1.25 l, such as soft drink bottles – make sure they’re empty, clean and dry)
- 2 balloons
What to do
- Gather your materials on a flat surface.
- Carefully use the drawing pin to make a hole in the bottom of one of the plastic bottles. Take the ballpoint pen and poke it into the hole to make it a little bigger. (If you don’t have a drawing pin, ask an adult to use scissors or a knife to make the hole - or get an adult to light a candle and hold the base of the bottle over the tip of the flame until a small hole is formed.)
- Holding the neck of a balloon, push the rest of the balloon into the mouth of the plastic bottle. Stretch the opening of the balloon around the mouth of the bottle.
- Repeat step 3 with the other balloon and plastic bottle.
- Find a friend to challenge. Make sure you give them the bottle without the hole, and keep the bottle with the hole for yourself!
- Blow through the mouth of the bottle to inflate the balloon. See who is the fastest at blowing up their balloon! (The person without a hole in their bottle will not be able to blow up their balloon.)
Questions to ask
Were you able to blow up your balloon? How long did it take you? (If you’re having trouble, try blowing up and letting down the balloon a few times before pushing it into the bottle.)
What happens if you make the hole in the bottle bigger?
To blow up a balloon, you need to force air into the balloon. The same thing needs to happen when you blow up a balloon inside a bottle. However, the bottle is already filled with air – when you try to add more air to the bottle by blowing up the balloon, the air inside the bottle needs to be compressed, which means that it can be squashed, to take up a smaller space. Compressing the air in the bottle is very difficult. Our lungs aren’t strong enough to do this, so it’s impossible to blow up the balloon inside the bottle without a hole in the bottle. The hole lets air escape, which makes space for the balloon to inflate.
Did you know
When you’re flying in an aeroplane at high altitude (more than 3,000 m above sea level), the outside air pressure is very low. If you weren’t inside the aeroplane, this could be dangerous for your health – humans can suffer from sicknesses at low air pressure, including:
- hypoxia (when body tissues don’t have enough oxygen)
- altitude sickness (which can cause headache and nausea)
- decompression sickness (when dissolved gases in the body turn into bubbles)
- barotrauma (caused by a difference in pressure between gases inside and outside the body).
To prevent these sicknesses, aeroplanes flying at high altitudes pump air into the cabin to compress the inside air. This means that the air inside the aeroplane is under higher pressure than the air outside the aeroplane. This is called cabin pressurisation.
(Sound of bubbles popping)
Rachel: Hi everyone, my name’s Rachel and I’m from the Questacon Science Squad. Today, we’re going to show you how to play a really cool trick on your friends.
(Camera pans down to table)
- 2 clear plastic bottles
- 2 different coloured balloons
- a ballpoint pen and
- a thumbtack
(Camera pans to Rachel’s face)
The challenge in this activity is to blow up a balloon inside a bottle, but here’s the trick your bottle is going to have a hole in it. So what you need to do, is take your bottle and puncture a hole in the bottom using the thumbtack.
(Rachel pushes a hole in bottle with thumbtack)
Next, take the ballpoint pen and make the hole bigger.
(Rachel uses the pen to make hole bigger)
Just like the one I prepared earlier.
(Camera zooms out to show the other bottle)
The next step in the process is to put the balloon down through the neck of the bottle and get the top of the balloon and stretch it over the neck of the bottle.
(Rachel puts balloon into top stretching it over the neck of the bottle)
And do it with the other one as well.
(Rachel puts a balloon in the other bottle)
And of course you need to invite someone to challenge you to a balloon bottle blowing competition. But make sure your bottle is the one with the hole in it. Here we go. Ah Tim, would you like to challenge me to a balloon in a bottle blowing competition?
(Rachel calls out to Tim)
Rachel: I am the 3 time Australian champion, are you sure you want to do this? OK, after I say go, Tim, let’s see who can blow the bottle up the f, [I mean] blow the balloon up the furthest inside the bottle. Are you ready?
Rachel: Set, Go!
(Camera zooms out to see both Rachel and Tim blowing up their balloons)
Rachel: Tim! What’s going on?
Obviously, I won that competition. If you’d like to know why Tim couldn’t blow up his balloon in the bottle, you can visit our website. And Tim, why are you wearing a dress? See you next time.