Lockdown project for kids: Crush cans with a bowl of water!

Can you crush a can with a bowl of water? A simple experiment to keep your kids and yourself busy.


Being at home with the kids for the last couple of weeks has, to be fair, been a little bit of a challenge. Just keeping them busy, without resorting to a screen has been a bit of a mission. Especially when I have been trying to also get an assignment for a study paper done, as well as update the sites and somehow try to keep the H&S project over at the GunSafe growing.

It did finally occur to me (which I have to wonder why it took so long) to include a little ‘science’ experiment in our daily activities. Just something every day to engage in a bit of physical learning.

I have realised, that I potentially enjoy these projects as much as the girls – as the project manager in me gets to flex the brain a little bit, and, the educator gets to think about how to put across some basic ideas to two little girls.

So – in the hope someone else might get some good ideas – I am going to document some of the projects were are up to. They are all simple and involve things likely already around the house.

To start – a classic – crushing cans with water!

What you need

  • Aluminum Cans
  • A big bowl of water
  • A gas cooker – the camping kind is fine – but basically anything to provide a direct heat to the bottom of the can.
  • Tongs
  • Safety kit

The Setup

“So girls – do you think you can crush a can with a bowl of water?”

This is an important part – you need to explore the idea a bit and set the stage. I am not so worried about setting a ‘hypothesis’ at this stage with the girls – it’s more just about doing some fun stuff.

“Hmmmm… I wonder what would happen if…”

The Execution

Fairly easy.

Get yourself a big bowl of water – essentially – it just needs to be big enough to put the entire mouth of the can into. Cold, but doesn’t need to be an ice bath.

Put about a tablespoon of water in the bottom of the can, and heat it over the cooker. You are waiting until you get a good boil and a pile of steam coming out the opening of the can. Hold it upright, with the opening to the top. You will see, hear and feel the water boiling in the can.

Once you have a good boil on, quickly tip it, opening first into the water.

I did the first one myself and then let the girls help out.

The Science

Essentially, by boiling the water in the bottom of the can, you are creating steam – the steam pushed the air out of the can, so when you then quickly dump it into the water, you close off the opening in the can, the reaming steam condenses and you are left with a vacuum in the can. The pressure inside the can is therefore much lower than outside, and the can ‘crushes itself’. Quick quickly and violently.

The phenomena you are seeing is phase shift – things changing from one state to another (water, steam) and unbalanced pressure (generating a vacuum in the can).​1–3​

Safety Considerations

Burns would be the primary one. Talk about about hot=burnies!

Make sure you have water in the can before putting it over the heat source – not doing so could result in the ink on the can vapourising, or the aluminium can itself melting. In a relatively open area, this isn’t a major concern – but worth avoiding anyhow.

I have googles for the kids – more for fun and ‘dress up’ purposes – I would put them in lab coats if I had them – but – not a bad idea.


  1. 1.
    Can Crushing. APS Physics. https://www.aps.org/programs/outreach/guide/demos/cancrush.cfm. Accessed 2020.
  2. 2.
    The collapsing can. Science if Fun. http://www.scifun.org/HomeExpts/COLLAPSE.html. Accessed 2020.
  3. 3.
    Watch the can collapse before your eyes. University of Wisconsin-Madison. https://wonders.physics.wisc.edu/collapsing-can/. Accessed 2020.