Explorit: Floating and sinking — water’s wonderful properties

By From page A5 | March 28, 2014

Can a paper clip float on water? If you think so, why? Is it light enough, or is there another reason? If not, why not? What would cause it to sink? Let’s try an experiment to find out what happens when paperclip meets water.

You will need: some paperclips, a cup or bowl of water, a piece of paper and some dish soap. Use a shallow cup or bowl so that in case a paperclip sinks, you can easily fish it out. Fill the cup or bowl about half way with water and let’s get started!

Try dropping a paperclip or two into the bowl. What happens? You’re probably noticing them sink right to the bottom. But does that mean that a paperclip can never float on the water? Let’s explore further!

Instead of dropping them into the bowl, try gently setting them on the surface of the water. Can you get one to float? If not, try placing a piece of paper under the paperclip and setting both on the surface of the water.

The paper and paperclip together should be floating, which tells us that the paperclip on its own isn’t too heavy to float. Now try gently nudging the paper so that it gets wet and sinks to the bottom leaving the paperclip floating on the surface of the water.

Why doesn’t the paperclip sink this time? The answer has to do with how water molecules behave.

Water molecules like to stick together. And when you put a bunch of them into a bowl all together like we did for this experiment they get sticky. Think about what would happen if you put your finger into the water. The water molecules would stick to your skin and you’d have to dry them off.

When water is in a cup or a bowl like this its “stickiness” creates a kind of skin on the top of the water. That’s called surface tension, and it allows light things to stay on the surface without sinking because they don’t break the surface tension. Some animals like the water strider insect use that surface tension to glide around on top of the water in ponds.

But we can change that surface tension by adding a little dish soap to our bowl. Squirt a little soap into the bowl and watch what happens to the paperclip. Does it stay floating for long?

The dish soap broke the surface tension and you can watch it sink to the bottom of the bowl. Now that the water’s skin is broken, the paperclip too will sink.

But why did our first paperclips that we dropped in sink? One reason has to do with force. Dropping them in allowed them hit the surface of the water hard enough to break the surface tension and sink to the bottom.

Water, the many ways it can change and how we interact with it will be one of the fun explorations Explorit’s summer science campers will embark on. They’ll explore the chemistry and physics of water as well as differences between fresh and salt water habitats for plants and animals while learning about conservation.

Registration for this and all of Explorit’s camps is open now at www.explorit.org. And stay tuned for more information about Explorit’s new exhibition on water coming Fall 2014!


Explorit’s coming events:

Explorit’s Beautiful World: Science and Art exhibition is open to the public from 1 to 5 p.m. every Wednesday, Saturday and Sunday, and every Friday from 3 to 6 p.m.  Admission is $5 per person; Explorit members, teachers and children 2 and under are free.

Summer Science Camp is coming!  Registration is open now.  Visit www.explorit.org for more information or to register.

— Explorit Science Center is at 3141 Fifth St. For more information call 530-756-0191, visit http://www.explorit.org or “like” us on Facebook at www.facebook.com/explorit.fb.

Lisa Justice

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