Pins in a Bottle: An Activity to Learn about Air Pressure

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What’s something that surrounds us all the time but we hardly ever notice or think about it?

Air!

In fact, air is pressing on us all the time.

And ‘air pressure’ is what we call the weight of the air molecules pressing down on everything on earth.

This ‘Pins in a Bottle’ activity provides a quick and simple way to demonstrate the concept of air pressure and to show how air is pressing on everything at all times.

Note: Find more science experiments on my Science Activities for Kids page!

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To do this activity, you will need the following materials:

A disposable plastic water bottle, filled with water and with the cap on
Multiple push pins (3-5 is a good number, but you can use more if you wish)

Tip: Do this activity outdoors or someplace where you don’t mind water spillage.

Keeping the cap on, invite your learner to insert several push pins into the bottle. Encourage them to insert the pins straight in and to insert them toward the bottom of the bottle, as this will provide maximum effect later on.

Once the pins are in, have your child check for leaks. There shouldn’t be any.

Now comes the fun part!

Have your child remove the pins.

Watch their amazement as no water leaks out – other than maybe a drop or two – despite the presence of several holes in the bottle!

Now, have your child remove the cap from the bottle.

(This is where you definitely want to be in a location where it’s okay for things to get wet.)

And voila! As soon as the cap comes off, the water starts leaking out the pin holes!

With cap removed, water begins to leak from the pin holes

The science behind the activity

So why doesn’t the water start to leak when you remove the pins from the bottle?

There are three forces acting on the water at the site of the hole made by the pin.

The force of gravity, which pulls the water down
Water pressure pushing the water to flow out the hole
Air pressure outside the bottle pushing the water back into the hole

Because the air pressure pushing the water to stay in the bottle is stronger than the water pressure pushing the water out, the water stays put inside the bottle.

However, things change once the cap is removed from the bottle. At this point, in addition to the three forces already mentioned, air pressure starts to push down on the water through the opening at the top of the bottle. With the addition of this added force acting on the water, it begin to leak from the bottle.

Pin in a Bottle is just one of a number of cool science activities that are part of my Air Pressure STEM Pack.

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