Science Experiment: Sink or Float #MotivationalMonday

Following on from our previous experiment about Germination, we decided to investigate whether things would float or sink. My little boy just going into Year 1 is very bright and inquisitive and just kept asking about things. I thought it would be a great way to see how much they learned and remembered from the last experiment, but also see how much they could apply to the new one.


First of all my five year old wrote out a list of materials, and then considered whether they would sink or float. From this list I collected as many of them as I could/thought appropriate and added a few of my own. I filled up a (sorry dirty) pink bucket with cold water and printed out some “investigation sheets”.


The first thing the sheet asked was: “What is the problem?” – we decided it was that we wanted to determine which products would sink and which would float: The teen told us that it was caused by the different materials having a different density. The experiment could have been made very complicated but I felt it more important that the 5 year old could understand the principles, and get to grips with some of the terminology used in a Science experiment, whilst the 10 year old getting to know which variables were which.


Simply for the independent variables (something that is changed in the experiment) we had the different objects we were using. You could have used the density, the material, the size etc. With the dependent variables (being whether they would sink or float. We discussed what the constant variables were and decided on the type of liquid drop in (water), the level and temperature of that liquid; how level the container was, that the height the objects are dropped from, and with how much force, and finally how long we wait to see the result. For the controlled variable we decided that we would use 2 pegs of different materials – so as to determine whether it was shape or material that had an effect.

For a more complicated hypothesis you could talk about different types of materials, or items with similar properties and what you would expect to happen. We simply hypothesised as to whether an item would sink or float.


My 5 year olds hypothesis:

Things that will float:

  • Paper
  • Lolly Stick
  • Duplo
  • Plastic lid
  • Foil dish
  • Sponge
  • Fabric material
  • Bubble wrap
  • Weetabix
  • Cardboard
  • Lego
  • Plastic peg
  • Wooden peg
  • Things that will sink:
  • Tissue paper
  • Glass bottle
  • Monkey nut
  • Stone
  • Rock


What is the Procedure?

If I were just working with my older son (aged 10) I would work more on getting him to think about drawing the apparatus and writing the method; however, I had a 4 and 5 year old eager to drop things into a big pink bucket of water. We agreed that we would use the tuff spot to make the ground level, we would gently place the items in, and we would wait for 1 minute before determining the result – measured by if the item had sank to the bottom, or floating on the top. We did not discuss until it happened but, items floating at the top but underneath the water were deemed as floating.


Our conclusions were simply which items floated and which sunk, however, we thought about other things we could think about for further investigations. We talked about different rock types, and this lead us to think about how quickly the items that sunk reached the bottom: Indeed the small stone went much quicker than the bigger rock. We talked about the possibility that things might be different if we used a different liquid, or if it were fizzy (a possible experiment with our new SodaStream), or if the water was hotter (I very eager 5 year old wanted to boil the kettle there and then!). During the experiment we thought about it in terms of material to build a boat. My 5 year old decided to see If the foil would still float with the weight of a rock on it (like a boat with a person inside).


Our findings were that the stone, rock, card and Weetabix did sink (note I put this in last and quickly got it out, but it didn’t go as mushy as I expected). When my 5 year old saw that the bottle floated he said that we were meant to take the lid off (because that wasn’t glass) – and indeed the bottle filled with water and sank – making his prediction right! The other items we had tested that floated were a plastic tray lid, a monkey nut, bubble wrap, a stick, a foil dish (flattened), tissue paper (which did surprise me), both plastic and wooden pegs, sponge, Lego, a lolly stick, and fabric material.


I am really pleased with how much my children remembered, could identify what the variables were, and generally just think about things. They now have all manner of ideas about how to build a little boat.