Investigate how to make the best raft using a variety of materials.
Early Learning Goal links
- Mathematics ELG: Numerical Patterns
- Understanding the World ELG: Past and Present
- Understanding the World ELG: People, Culture and Communities
- Understanding the World ELG: The Natural World
- Expressive Arts and Design ELG: Creating with Materials
STEM vocabulary to introduce
Float, sink, sunk, sank, rise, rose, risen, size, big, small, heavy, light, bottom, top, surface, under, side, shape, predict, test
Before you start
You could introduce the activity by reading Charlie’s Boat by Kit Chase or watching the episode of Cbeebies’ Messy goes to OKIDO.
Show the children the marine engineer poster and tell them 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, 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.
Today they are going to be marine engineers and use their creative skills to build rafts. They are going to be curious and investigate how to make the best raft for the animals so they can float across the water tray/bucket to the other side without getting wet or falling in.
What to do
Show the children the pictures of different rafts. You could use our raft photographs.
You could ask:
- Can you remember what it means if something floats?
- What does it mean if something sinks?
- What can you tell me about the shape of the rafts?
- Are they flat or do they have sides?
- Do they look like boats? Why or why not?
Show the children the selection of materials they can choose to build their rafts. Remind them they need make the best raft for the animals so they can float across the water tray/bucket to the other side without getting wet or falling in.
You could ask:
- Which objects have we found before that float? What were they made from?
- If you read the book or watched the clip you could ask: What did Charlie/Messy use to make a boat/raft in the book/clip?
- Which material will you choose and why?
- Do you predict (think) that it will sink or float?
Tell the children that they are going to test their materials. Demonstrate how to place the material carefully onto the water. Show what happens if you throw it in or push it under. Invite the children to carefully place their material onto the water.
You could ask:
- Is your raft sinking or floating?
- What do you predict/think will happen when we put the animal/figure on? Why?
If the material sinks, remind the children that marine engineers are curious and want to know what happens. It doesn’t matter if the material sinks, as long as we have found this out. Remind the children that marine engineers are resilient. If the first material they pick doesn’t float, they can choose another one.
Demonstrate how to carefully place the animal/figure onto the raft. Show what happens if you throw it on or push down. Invite the children to carefully place the animal/figure on top of their material.
You could ask:
- Is the raft floating or sinking now?
- Why do you think it sank (if it did)?
- Why do you think it floated (if it did)?
- Do you think (material) would be a good choice for making a raft for you to float on?
As earlier, if the raft sinks, remind the children that marine engineers are curious and want to know what happens. It doesn’t matter if the raft sinks, as long as we have found this out. Remind the children that marine engineers are resilient. If the first material they pick doesn’t float, they can choose another one.
Show the children how to gently push the raft to the opposite side of the water. Invite the children to do this one at a time to avoid collisions.
You could ask:
- Does the raft still float?
- Which material do you think made the best raft and why?
- What is the best choice for a marine engineer to build a raft?
As earlier, if the raft sinks, remind the children that marine engineers are curious and want to know what happens. It doesn’t matter if the raft sinks, as long as we have found this out. Remind the children that marine engineers are resilient If the first material they pick doesn’t float, they can choose another one.
Other things to try
- If you have time and the children are still engaged, they could repeat investigation with different materials.
- You could try to attach lolly sticks or sticks from the outdoor area together to build rafts. You could try to use small elastic bands, string or glue.
- The Scout Association has a teeny tiny raft building activity that could help you.
The science of floating and sinking
We have put together some useful information about the science of floating and sinking 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!
Why do some materials sink and some materials float?
There are two forces acting on objects in the water. The weight of the object pulls down, while the upthrust of the water pushes it up. If the weight of the object is equal to, or less than, the upthrust, it floats. Things that float are buoyant. If the weight of the object is greater than the upthrust, the object will sink.
What is upthrust?
This is the upward force pushing towards the surface. When you try to hold a beach ball, empty plastic bottle or inflatable under the water, you can feel this force pushing it towards the surface. The upthrust force is equal to the weight of water displaced by the object.
Why do some materials float then sink (such as paper or sponge)?
Some materials are light because they are full of holes! Sometimes these are holes you can see, like in a sponge, but some are tiny holes that you can’t see, like in paper. The holes are full of air. Air is not heavy enough to push down into the water, and so materials that are full of air, float. When the materials full of air holes are floating, the water starts to fill up the air holes. The water soaks into the material and makes the weight to pulling down bigger than the force of the water pushing upwards.
What you’ll need
- A water tray, paddling pool, bucket or bowl, indoors or outdoors.
- A plastic animal or figure to build a boat for (about 10-15 cm in length/height
- Materials for building a raft: paper, card, polystyrene, balsa wood, plastic, tin foil- include some that will float and some that will sink. Try to make these roughly the same size if you can.
- Pictures of rafts pdf
- The marine engineer poster
10 minutes or so.Marine Engineer poster