What is an experiment to teach my daughter about steam (water) pressure?

On a recent steam train trip my daughter said to me:

Daddy, I'd like to pull that steam engine apart and see how it works.

Now there are two parts to her question - and I'm only make this physics question about one of them:

1. How do you learn about pistons driving wheels?
2. How do you learn about heating water to create pressure?

Now I don't want to just draw a picture or show her a video. I want something tactile, that she can experiment with herself (with supervision).

Thankfully - for question #1 - there are abundant toys online that show how air pressure pistons work to drive wheels and cars.

But for the second one - you could by a Stirling Engine (they're a little pricey) - but surely a home experiment would suffice?

When I told her that heating water to create steam creates pressure like a deflating balloon she said:

No it doesn't, the steam just floats gently out of the top of the kettle, there's no pressure.

I'm trying to design a home experiment for my daughter to show steam pressure - that is still understandable enough for an eight-year old.

My question is: What is an experiment to teach my daughter about steam (water) pressure?

• We really can't advise you about safety here, sorry. I suppose you could edit this to ask how to demonstrate steam pressure to someone like your daughter, leaving the safety aspect for you to determine separately using appropriate resources, and that might be okay. May 13, 2018 at 8:20
• I have first hand experience with this: you can make iced coffee frappé by shaking water and instant coffee and ice in a shaker. I tried to make hot coffee the same way and ended up with second degree burns on my chest. May 13, 2018 at 11:58
• A pressure cooker should be illustrative. Feb 17, 2022 at 20:26

I'm not advising that you do this, but when I was a boy I used to enjoy heating a small amount of water in a clean, otherwise empty, strong-walled tin with a push-fit lid. In the UK, a Lyle's golden syrup tin was (and is) ideal. The lid blows off with quite a convincing amount of kinetic energy. One needs to keep well clear. On no account use a tin with a screw-fit lid or an improperly-cleaned can that had contained inflammable material.

A good example to show how temperature affects pressure is to drink water out of a weak plastic bottle, place the bottle in the refrigerator for a few hours and show that the plastic has slightly collapsed, do the same thing except leave the bottle in a hot car or some other warm environment to see how the plastic bloats up. This is safe and will show pressure changes inside the bottle.

From there you just say that with a lot more heat the pressure changes a lot more, etc.

What about the rattling of the lid on a pot of boiling water? That doesn't seem very gentle.

One of the main problems with experiments like this is that steam can be surprisingly dangerous. I would advise against using home built examples and stick with an off the shelf option.

However that does not mean a sterling engine or some micro steam set would be your only choice. To give an idea to experiment using normal household objects try looking at a moka pot or pressure cooker.

here is a high chance you already have or can borrow one or both. If not, A moka pot or similar percolating cofee pot isn't very expensive to get new or second hand. Both products also have the added benefit of being useful outside of the experiment.

With the pressure cooker, you can simply put some water in, boil it without a lid and show that the water boils away like a normal pot. Then, put the lid on, let it come up to pressure and release the pressure valve. Steam will shoot out with speed and power.

The moka pot is similar, albeit a bit more abstract. You can once again show that water is boiling and steam is floating away. But when putting it together and showing that the water is pushed up through the cofee grinds and up the tube, ending with a bunch of spurting steam that escapes shows that steam has pressure, and that it's enough to push things. (of course there is a technicality with expanding air contributing here, but I don't think that invalidates what you're trying teach)