Experiments with Water

Rainy days can be the perfect opportunity for children to experiment with water. One example of this was a child playing with conkers in some different measuring containers filled with water. In the image below, we can see the child’s experiment.

Many areas of maths were explored in this experiment, including spatial reasoning. At one point, the child predicted that one container was bigger than the other. They then demonstrated this by pouring the contents of the smaller container into the large container and showing that the larger container was not full.

This is a great exercise in comparing the capacities of containers and justifying predictions. The shape of a container can sometimes be misleading. For example, even though one container is taller than another, it might not hold as much water as the shorter container. This is because the cross-sectional area of the containers might differ. By measuring the amount of water different-sized containers can hold, children could order containers by capacity.

In their experiment, the child also observed that as conkers were added to the container, the level of the water in the container rose. This was a great observation of displacement.

Displacement is what happens to a liquid when an object is submerged. As the object sinks (or partially sinks if it floats), the level of water in the container rises as the object forces the water out of the way.

When an object is fully submerged, the volume of water displaced is equal to the volume of the object that has been submerged. We can then experiment with finding the volume of different objects by constructing our own version of a eureka can. We can place a bucket inside a tray and then fill the bucket to the top with water. The bucket must be as full as possible. Next, we can place an object into the bucket, and water should spill out into the tray. We can then measure the amount of water in the tray, and the volume of this water will be equal to the volume of the object.

The piece of equipment normally used for this experiment is an eureka can. Eureka cans take their name from the story of Archimedes and the golden crown. The story goes that Archimedes was asked to determine if a crown was made of pure gold. He could weigh the crown, but had no way to measure its volume to check if the crown had the density of gold. Then one day, he found inspiration when seeing how the level of the bath water rose as he got in. He shouted eureka, giving the can its name. He filled a container with water and measured the water displaced when submerging the crown to find its volume.

Some other children discovered that adding objects to a container of water can change the water level in the same way as a eureka can. They began by filling a jug to the top with water “ahhhhhh, it splashing, the water full”. Following the nursery practitioners’ suggestion, the children then put their hands in the jug, causing more water to spill out. When they removed their hands, the water level was lower. A volume of water the same size as their hands had left the container. “It gone out. The water spill out.”

The children then refilled the container and experimented with adding small pumpkins.
“Do you think the water will stay in the jug when we put the pumpkins in?”
“No no stay out.”
“You think the water will come out of the jug?”
“Yeah it gonna come out.”

The water did spill out as the pumpkins were added to the jug. Once the children removed the water, they then saw that the water level was much lower.
“It full, now it lower down. It all camed out.”
“You’re right, the water did come out of the jug, all the pumpkins took the space for the water didn’t they?”
“Yeah no space for water now.”

If the children had measured the difference in the water level, they would have found the volume of the pumpkins. In the image below, you can see the children’s experiment.

Another fun experiment for children to explore is filling up containers with changing cross-sectional areas. For example, bottles are usually narrower at the top and will fill slowly at first and then quickly as the neck of the bottle is reached. Experimenting with filling different containers in this way could lead to discussions about cross-sectional area and how this affects the speed at which the water level rises.

For more experiments with water, please see our article on buoyancy.