Sink or Float Experiment

Even the most simple science experiments can amaze kids. We tried out the sink or float experiment. Not only is this a fun guessing game, but it teaches them about density!

Here are a few items that can be used for the float & sink experiment. This is only a few ideas. Anything can be used so long as it is waterproof of course!

Lego Pieces
Coins
Rocks
Boiled Egg
Plastic Egg
Toy Car/Animal
A Screw
A Pencil
An Eraser
Foam Block
Metal Spoon
A Ball

Making Predictions

Gather up some items from around the house and draw a graph. Our graph had 3 sections, one for guessing, one for sinking items and one for floating items. My son wanted to make his own graph but I have made a couple of printables for your convenience.

I have attached 2 FREE printable graphs for your convenience! Grab them BELOW!

We marked an F for float and an S for sink.

Surprising Results

We then dropped the items into the water after some guessing. Items began to sink but then bounced back up to the top.

It’s great to watch your little students take guesses before they filled out their answers. As a result they were surprised that some of the things didn’t react the way they thought they would.

Floating Lego Man!

This was a fun activity that didn’t take up much prep. We could have actually used more items if we had a bigger tub. A regular bowl or even the bath tub would work.

However you can use pretty much anything you have that holds water. An old fish tank works great as it’s see through and you can watch the items drop down. This activity can also be done outside on a nice day.

What Did We Learn?

We learnt that everything around us is made up of tiny molecules. Some objects are jam packed together and other objects are loosely packed together.

The objects that are jam packed together have a higher density than the items that are loosely packed together. Which means they are more likely to sink.

We learnt about buoyancy and gravity. Gravity being a force that pulls an object down, and Buoyancy being the upward force that keeps things afloat.

This activity can be done again and again with different objects.

Other great ideas for sink & float

Try placing a floatable object in the water, and placing items on it to see if it still floats.
Use a straw to blow floating items around in the water, to see how light they are.
Get the kids to put an empty bottle into water, then to fill the bottle to see the difference. What happens to the bottle once it is filled with water?
Try making your own boats to test out on the water. Check out our DIY floating sailboats and rafts. https://crafty-mummy.com/diy_boats_and_rafts/