Use water displacement to rescue objects from a container of water.
Early Learning Goal links
Mathematics ELG: Numerical Patterns – Compare quantities up to 10 in different contexts, recognising when one quantity is greater than, less than or the same as the other quantity;
Understanding the World ELG: Past and Present – Talk about the lives of the people around them and their roles in society;
Understanding the World ELG: People, Culture and Communities – Describe their immediate environment using knowledge from observation, discussion, stories, non-fiction texts and maps;
Understanding the World ELG: The Natural World – Understand some important processes and changes in the natural world around them, including the seasons and changing states of matter.
STEM vocabulary to introduce
Sink, float, up, down, top, bottom, surface, water level, predict, more, less
Before you start
You could introduce the activity by reading Mr Archimedes’ Bath by Pamela Allen.
Show the children the marine engineer poster and tell the children that they are going to be marine engineers for this activity.
Ask the children if they know what a marine engineer does. Marine engineers make and fix boats and ships, submarines, oil rigs and drilling equipment.
Tell the children about the attributes. Marine engineers are:
Curious and want to know which materials sink and float.
Creative when they design and build things like boats, ships, submarines and oil rigs.
Resilient when their ideas or designs don’t work the first time – they try again to get it right.
Tell the children that they are going to be curious like marine engineers and work out how to get an object to the top of a container without touching it.
What to do
Show the children the containers half filled with water, with the objects floating in them.
Ask the children how they think they could get the object to the top of the container without touching it.
Remind the children of the Mr. Archimedes’ Bath story. You could ask:
What happened to the water when the animals got into the bath?
What happened to the water when the animals got out?
Give the children a stone/marble each and tell them that they are going to drop the stones/marbles etc into the water.
You could ask: What do you think will happen?
Ask each child to take a turn dropping one stone in.
You could ask: What do you think is happening?
Explain to the children that the stones are taking the place of the water and pushing it out of the way, just like someone who pushes into the line! The water can’t go anywhere as it is trapped in the container, so it has to move upwards.
Put stones/marbles into the container until the water reaches the top. Encourage the children to count along with you. Make a label for the container showing how many stones it took for the water to reach the top. You could get one of the children to do this. Repeat the activity for all of the containers.
You could ask: Do you predict/think you will need more or less stones to get the object to the top of this container? Were you right?
When all of the objects have reached the top of the containers, you could ask:
- Which container needed the most stones to get the water to the top?
- Which container needed the least?
- Why do you think this is?
- Do we need to use more or less marbles/stones for tall, thin containers?
- Do we need to use more or less stones/marbles for wide, flat containers?
If the children in your setting are not yet ready to count, you could put the marbles/stones they you put into each container onto a plate so that the children can compare the amounts this way.
Other things to try
- Try using containers that are the same size (or use the same container) and add different objects to see how much water is displaced each time. You could add anything that sinks, such as a large stone, toy car or set of keys.
- You could measure the before and after level on your container.
The science of water displacement
We have put together some useful information about the science of water displacement to accompany this activity. Don’t worry, this is for your information only and to help you answer any questions children may have. We don’t expect you to explain this to the children in your setting!
What is water displacement?
When an object goes into the water, whether it sinks or floats, it takes up some of the water’s space, and the water is displaced (moves out of the way). When we half-filled our container with water and added stones to it, the water couldn’t go down or sideways as the container was in the way, so it has to go upwards. We could see the water level rise as the stones took up space in the water.
Do floating objects also displace water?
An object floating on the water also takes up space. To make this space, some of the water is displaced. The amount of water displaced is the same as the volume or amount of the object that is below the water. The more weight you add to the object, the more water it displaces. As the volume of water displaced increases, the force of the upthrust increases to balance this, and the object floats. There will eventually be a point where the weight of the object becomes greater than the upthrust and the object sinks.
What you’ll need
- Lots of different sized containers, cups, measuring cylinders etc filled about half full with water
- A tray/tough spot or space outside
- Marbles, glass beads or pebbles to displace the water. These must sink for this to work. Don’t use anything too small or the activity will take far too long!
- An object that floats. An animal/figure would be best, one for each container if possible
- Pen and paper/post it notes for making labels
- The marine engineer poster
10 minutes or so.Marine Engineer poster