Grade 6 · Science · Unit 4 of 12
Buoyancy
Why things float or sink.
What your child practises
Practises the idea that a fluid pushes up on objects, why some things float and others sink (density, shape and the fluid), and how ships, submarines and life jackets use buoyancy.
Nunavut Curriculum approved guide: NWT Science and Technology K–6 (2004), Physical science · buoyancy: balanced and unbalanced forces, density, and floating and sinking
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Which would sink in water?
- a cork
- a steel bolt
- a beach ball
a steel bolt
Hint: Steel is more dense than water.
Question 2
An object is less dense than water. It will…
- disappear
- float
- sink
float
Hint: Less dense objects float.
Question 3
A cork bobs up to the surface. The buoyant force on it is…
- less than its weight
- greater than its weight
- zero
greater than its weight
Hint: The upward force wins, so it rises.
Question 4
Why does a life jacket help you float?
- It makes gravity weaker
- It is full of material that is less dense than water
- It makes you heavier
It is full of material that is less dense than water
Hint: The jacket adds volume without much mass.
Question 5
Why does a large steel ship float?
- Gravity does not pull on ships
- Its shape holds a lot of air, so it is less dense overall
- Steel is lighter than water
Its shape holds a lot of air, so it is less dense overall
Hint: The ship pushes aside a large amount of water.
Question 6
Why can a person float more easily in the Dead Sea than in a lake?
- People weigh less there
- The water is warmer
- The water has much more salt, so it is denser
The water has much more salt, so it is denser
Hint: A denser fluid pushes up harder.