How to Make a Water Bottle Cap Pop off with Air Pressure

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There is a cool trick using an empty plastic bottle and air pressure that will allow you to shoot the cap of the bottle across the room. The cap is capable of coming off with quite a bit of force, so be sure not to aim the bottle at anyone. Compressing the gas inside the bottle and forcing it into a smaller space causes the air pressure to build. Releasing the cap unleashes this pressure and launches the cap across the room! [1]

Part 1
Part 1 of 2:

Using the Twist Method

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  1. Obtain an empty plastic bottle . This experiment works best with a bottle that has relatively thin plastic. You need to be able to twist the bottle, so bottles made of thicker plastic will be difficult to use. You also want to use a standard size (16.9 oz or 500 mL) bottle or larger, not the miniature ones.
    • You want the bottle to be mostly empty: if you leave a small amount of water in the bottom of the bottle, you will see a cloud of water vapor form at the end. [2]
    • Bottles with smaller lids also tend to work better.
  2. While this step isn’t entirely necessary, it can make it easier to twist the bottle for the experiment.
    • Recycle the label when you’re done with the experiment.
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  3. In order to build up the air pressure inside the bottle, you need to decrease the amount of space available by crushing the bottle. Start by squeezing the middle of the bottle and twist the bottom. [3]
    • Starting the twist can be difficult. In some cases it can be easier if the bottle starts out slightly deflated. Remove the cap, squeeze the bottle a bit and replace the cap while keeping the bottle slightly squished.
    • Make sure the cap is tightly screwed on to the top of the bottle before beginning this step.
  4. As you twist the bottle, you will notice it will become more difficult. Twist the bottle as many times as you can until you can’t twist it anymore. If you are not strong enough to do it, ask an adult for assistance. [4]
    • Keep the bottle pointed away from your face and others while you are twisting the bottle. While it is unlikely for the bottle to pop during this step, it is possible.
  5. Grasp the bottle tightly against your stomach with the cap facing away from you. Use the side of your thumb to quickly twist the cap off. Make sure you fully twist the cap off, or the cap won't pop out. If done successfully, the cap should fly across the room.
    • Another way to pop the cap off is to hold the bottle between your legs and then twist it with your hand.
    • If the cap does not fly across the room, there wasn’t enough air pressure built up inside the bottle. Untwist the bottle, blow into it to refill with air, and try again. [5]
  6. When the cap flies off you may notice that a cloud of white vapor is coming out of the bottle as well. This is water vapor that is formed when the cap gets released. As the pressure builds inside the bottle, the water molecules get squeezed together. When the cap goes off, the temperature inside the bottle cools causing the water molecules to condense into vapor.
    • This is also how clouds form in the sky. At cooler temperatures, the water vapor forms around dust particles to condense. [6]
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Part 2
Part 2 of 2:

Reusing the Bottle

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  1. Once you have launched your cap, you can do it over and over again until you get bored. Untwist the bottle until it is back to its original shape. The bottle will be a little bit crunched but it will still work. [7]
    • If the plastic cracks at any point in the bottle, it will no longer work for this experiment.
  2. Place your mouth around the top of the bottle and blow into it until the bottle puffs up again. You will hear a crackling sound as the plastic inflates. It does not need to be completely full, it just needs to have enough air inside it to compress. [8]
    • Don’t share bottles with multiple people to avoid the spread of germs.
  3. Replace the lid on the bottle and squeeze in the middle as you did before. Repeating the same steps, twist the bottle until you can’t twist it anymore. Remember, the more twists you can get, the more pressure that will build up inside the bottle. [9]
    • The bottle should begin to twist more easily the more times you use it.
    • At some point, the plastic will likely crack and you will not be able to use that bottle anymore.
  4. Position the bottle against your chest with the cap facing away from you and twist it off. Watch it shoot across the room again as the air pressure gets released. Repeat as many times as you’d like or until the bottle cracks. [10]
    • Remember, never aim the bottle towards a person or an animal.
    • Avoid pointing the bottle at your face as well.
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Expert Q&A

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  • Question
    Why isn't my water bottle twisting?
    Bess Ruff, MA
    Environmental Scientist
    Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group.
    Bess Ruff, MA
    Environmental Scientist
    Expert Answer
    The plastic of your water bottle might be too thick if you're having difficulty twisting it. Try to find a bottle constructed out of thinner plastic.
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    Not Helpful 9 Helpful 26
  • Question
    What happens if I breathe in the vapor?
    Community Answer
    Nothing. Water vapor is partly air, therefore it'd basically be like breathing in steam.
    Thanks! We're glad this was helpful.
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    Not Helpful 15 Helpful 35
  • Question
    Do I need a small amount of water in the bottle for a water bottle cap to pop off with air pressure?
    Community Answer
    No, I've seen my friend do it, and the top came flying off without any water in the bottle.
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    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
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      References

      1. ↑ https://www.youtube.com/watch?v=cUWoQcLs2-k
      2. ↑ https://www.youtube.com/watch?v=cUWoQcLs2-k
      3. ↑ https://www.youtube.com/watch?v=cUWoQcLs2-k
      4. ↑ https://www.youtube.com/watch?v=cUWoQcLs2-k
      5. ↑ https://www.youtube.com/watch?v=TWsfeRbHQdg
      6. ↑ http://www.weatherwizkids.com/weather-clouds.htm
      7. ↑ https://www.youtube.com/watch?v=TWsfeRbHQdg
      8. ↑ https://www.youtube.com/watch?v=TWsfeRbHQdg
      9. ↑ https://www.youtube.com/watch?v=TWsfeRbHQdg
      1. ↑ https://www.youtube.com/watch?v=TWsfeRbHQdg

      About This Article

      Article Summary X

      With the right technique, you can make your water bottle cap pop off with air pressure. You’ll need an empty plastic bottle with relatively thin plastic for this to work. Squeeze your bottle in the middle and twist the bottom. Keep twisting the bottle as far as you can go. This will help build up air pressure by reducing the available space inside. If you’re struggling to twist the bottle, try taking the cap off and squeezing it a tiny bit to remove some air and replacing the cap. When you can’t twist the bottle any further, grasp it tightly against your stomach with the cap facing away. Then, use the side of your thumb to quickly twist the cap off. The cap should fly across the room and a small cloud of vapor should come out the bottle. For more tips from our Science co-author, including how to reuse your bottle after twisting it, read on!

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