Lesson by R Bowen
Learning Intentions:
- To make a simple prediction based on scientific understanding
- To be able to write a short explanation with a labelled diagram
Step 1: Activity overview for parent, carers and pupils
In this activity your child will develop their understanding of buoyancy of objects in water and how this is affected by the amount of salt in the water.
There are two short videos to watch, approximately five minutes in total. The main activity can be completed offline.
You will need the following resource for this activity:
- An egg
- A large bowl (enough to easily contain 1 litre of water)
- Salt
- Spoon
- Optional resource: A tall glass (wide enough to hold an egg)
Step 2: Introduction to the activity and additional information
Have you ever wondered why people can float in the Dead Sea? Have you ever wondered about the effect of salt water and buoyancy? Watch this short video to develop your understanding of salt water (salinity) and its effect on how things float (buoyancy).
Question: How much salt is needed in water to make an object that would normally sink, to be buoyant?
Step 3: Tasks to carry out for this activity
Activity 1
Part 1
- Pour at least 1 litre of tap water into a large bowl, jug or container. You will need your water to be at least 15 cm deep.
- Make a prediction of what will happen when you carefully drop an egg into the water.
- Will it sink? Will it float – is it buoyant?
- Can you think of a scientific reason for your prediction?
Part 2
- Did your egg sink?
- That’s right, it should sink in tap water. Can you explain why?
- Now predict how many spoons of salt will it take to make the egg buoyant (float).
(Note: fresh eggs sink. If the egg has gone off it will float, this is because it will have air inside it which makes it more buoyant.)
Part 3
Carefully add a spoonful of salt and make sure to stir the salt until it is dissolved. (You should not see any salt in the bottom of the bowl or container once it is fully dissolved.)
- Put your egg back in the water. Did it float?
- If not keep adding a spoonful of salt at a time making sure it has fully dissolved before testing your egg again, until your egg becomes buoyant.
- How many spoons of salt did you need to add to get your egg to become buoyant?
- How accurate was your prediction?
Part 4
Now write an explanation for why things float in salty water including a labelled diagram.
- In your introduction remember to include details about the experiment you have undertaken, including detail about it being a fair test e.g. size of spoon used, amount of water etc.
- Apply your findings to help you with your explanation.
- Remember to use words such as dense, density, buoyant, buoyancy, increased.
Click on the link below to remind yourself about the feature of an explanation text.
Once you have completed the task you can email anything you create (photos, documents, screenshots etc.) directly to your teacher or directly upload it to any of the available places in Step 6.
Step 4: Look over the success criteria for this activity:
Success criteria #1: I can make a sensible prediction
Success criteria #2: I can create a salt water solution that makes an egg buoyant
Success criteria #3: I can write a scientific explanation and draw a diagram that explains buoyancy.
Step 5: Extension and follow on activities/challenges (optional)
Activity 2
- Try to see if you can make your egg float in the middle of a glass.
- Can you explain how you did this?