Sinking and Floating

To experiment with objects that sink or float, and foster curiosity as to why.

Many children know about floating and sinking as they have experienced this frequently, either in the bath or in the pool. Floating objects are fun to play with but children may not have come to a realization as to why things float or sink and so this demonstration can be a fun learning experience.

This theme could also tie in with a pirate storytime and you could set up a clear water container with sand at the bottom and a treasure chest. 

Science concepts/experiments

 

Water experiment
What types of objects float and what sinks?
Fill a large see-through bowl or container with water.
Collect a variety of different items to test is they sink or float.  Corks, coins (look at small coins compared to large coins), pencils, feathers, paper, stones etc.  Get the children to vote on whether they would sink or float.

Compare the properties of some of the objects.  For example a small coin and a cork weigh about the same however they act differently in the water. Ask children if they have any ideas of why this would be.
Discuss that what objects are make of is important.
Discuss the size of objects and whether you can tell if it will sink of float.
Look at objects that may absorb water such as a sponge or paper which will float for a time but then sink.

Some fun 'tricks' to try in your water container
Find a volcanic rock (pumice rock)and an ordinary rock of a similar size.  The volcanic rock will float as it is filled with air.
Test out a Coke can as compared to a Diet Coke can. You can see what happens here 

Diver in a bottle 
Equipment: plastic bottle, pen lid (not one with a hole in it), plasticine/bluetac.


Fill bottle almost to the top.  You will need to add plasticine to the stem of the pen lid and place in the bottle.  If the lid sinks, remove from bottle (you will probably have to remove all the water just to get the lid out) and remove some of the plasticine.  You need to get the pen lid to just float on the top of the water.  Once this is achieved fill the bottle to almost the top and screw on bottle top well.
Squeeze the sides of the bottle.  What you should see is the pen lid 'diver' sink to the bottom of the bottle.  When you release the bottle the 'diver' returns to the top.


What happens in this experiment is that there is a small air bubble trapped at the top of the pen lid.  When the bottle is squeezed it increases the pressure inside the bottle which decreases the size of the air bubble and the 'diver' sinks.  Once you stop squeezing there original pressure returns, the air bubble expands and the 'diver' rises to the top.  More information on this experiment can be found here


This experiment pairs well with the book Ruby learns to float by Phillip Gwynne where the story talks about Ruby breathing in in order to float.  Talk about how air is needed to float and then explain why the diver sinks. 

Book ideas:

 

What floats in a moat? – Lynne Berry
Ruby learns to swim – Phillip Gwynne
Who sank the boat? – Pamela Allen
Mr Archimedes Bath – Pamela Allen

Craft:

Make a paper boat

Extra Learning:

During craft time some of the children came up and played with the container of water testing out the objects for sinking and floating. I encourage this curiosity in the children.  Some of the children decided that they could float the boats they made.  They discovered the the boats would sink for a while and then sink.  A lot of the children went home with soggy boats!