Before starting the experiment I explained to my son that he was going to investigate whether the object sinks or floats. I also told him that the word sink means that the object goes downwards or breaks the meniscus the surface of the water, because it is heavy. Floating or buoyancy, oversimplified means that the object stays on the surface, it doesn't sink (negative buoyancy); objects with less weight and a buoyancy friendly design (boat or water craft) tend to float.
I explained to him that he was going to drop the objects into the bucket of water one by one so we could analyse. I expressed this before the object he designated was released, and he had to predict whether it would sink or float. The question I asked was: Is it going to sink or float? Why? I wanted my son to think of the reasons for his answer hence why I asked him to tell me why. I expected him to tell me it would float because its light/or heavy.
The first thing he dropped in the bucket of water was the cork. He predicted that the object would float but could not explain why. Which begged the question, is the cork heavy or light? He answered light and I reinforced my point to him by saying that light objects float, heavy objects sink.
Afterwards he took the empty small container to investigate our first buoyancy experiment. I asked him to think of the following questions:
- Do you think the container will float or sink? He said that it would float.
- What happens if you add coins to the container? He was very excited to try using coins. He firstly added 5 coins but it was still floating. He continued adding more and more coins, until it finally sank which made him quite happy :)). I asked him to count how many coins he put into the container to make it sink, and the result was 47 coins. He had fun adding and counting the coins.
I took a piece of aluminium foil to pretend it was a ship and he placed a coin onto it to make his analysis. He answered correctly saying the coin would float when it was on the ship, however, it would sink when releasing it minus a flotation device on the water. I reminded him that metal materials are not designed to float, it may sink.
He also tried with his Batman toy. He was surprised to learn the Caped Crusader sank, and he told me that when we go to the beach we sink too if we go too far :))).
He also analysed other materials such as the popsicle, many toys and a ship made with a bottle of water. He also put water inside the bottle which sunk immediately.
This a great science activity that does not cost anything and it is quite enjoyable. It also develops the ability of predicting future events, as well as analytical thinking.