I should probably start by saying this experiment didn’t work. We have tried to get it to work, we really have (see tips/extra bits for all the variations and modifications) but there just hasn’t been much success. However I thought I’d write it up as someone might be able to make it work (I have seen proof on the internet that it can happen, although I guess you can’t always trust what you see on the internet). If you are successful then let me know!
What you need:
- Bowl of water (essential – see through is helpful as just gives more visibility as to what is happening)
- Carrot (essential)
- Cocktail sticks (essential – some say these help the carrot sink, although mine did it without, others say they make the carrot more buoyant. Either way they are apparently essential)
- Screwdriver (or something you can make a hole in the carrot with)
- Baking powder (essential)
What to do:
- Cut a chunk of carrot and then cut a slice off one side to give it a flat bottom.
- Use the screwdriver to make a hole in the middle of the flat bit but don’t go all the way through to the other side.
- Add cocktails sticks at either end of the top of the carrot in a V shape (either 2 on each end or break one cocktail stick in half for each end).
- Fill the hole in the carrot with baking powder (stuff it in).
- Pop carrot the in water and watch as it beautifully sinks and floats and then sinks again (??!).
- It’s worth drying the carrot before you put baking powder in so that it doesn’t start fizzing until it is in the water.
- You definitely need baking powder and not bicarbonate of soda.
- We tried different sizes carrots. We tried different sized holes filled with baking powder. We tried cold carrots and room temperature carrots (my super clever husband thought this might make a difference. I thought he was on to something but sadly he wasn’t). We also tried salt in the water, to help the carrot float, but this didn’t work. We googled it (lots of people have made this work!) and tried my cocktail sticks in a slightly different position. None of these things really worked. We did get the carrot to rise but it also fell to one side and so all the bubbles escaped, which wasn’t really the right effect. We tried repositioning the cocktail sticks again to stop this happening. It didn’t work. We had a cup of tea and a fruit yoyo, and gave up.
(Bubbles!! Didn’t make it rise though).
The science bit
With (or without) cocktail sticks the carrot sinks because it is too heavy to float. The baking powder reacts with the water and produces carbon dioxide (the bubbles). Because these bubbles are made underneath the carrot they help to push the carrot to the surface of the water. The bubbles then pop and the carrot sinks back down. Real submarines rise by filling tanks called ballast with air and then letting the air out again to sink.
Explaining it to children
Carrots are heavy and so they sink. However the hole in the carrot is filled with baking powder that has a chemical reaction with the water. A chemical reaction is when different substances (like water and baking powder) are mixed together and produce something else. Here the baking powder and the water mix together and this produces bubbles of a gas called carbon dioxide. These are the bubbles you can see in the water when you put the carrot in. These bubbles help to push the carrot up. When they get to the surface of the water the bubbles pop and so the carrot sinks again. I couldn’t really explain why it didn’t work, but it was kind of fun trying to work it out with my little lab assistant.
(This is what happens when your child is in charge of administering the baking powder).
Experiment based on an activity from the fantastic Usborne Activities: 365 Science Activities book.