Floating & Sinking
Science: KS3, topic 3.2.26
Floating and Sinking
Objects that float rest on the surface of the water. Objects that sink descend below the surface of the water.
Floating
- Objects that float are less dense than the substance they are floating on.
- If an object is able to float, it is described as buoyant.
Weight and Upthrust
- A floating object’s weight is less than the upthrust of the water.
- Or the weight is equal to the upthrust of the water.
Ships Floating
- Heavy objects like ships are able to float on water.
- Ships float because they displace lots of water.
- So there is an increase in the upthrust.
Upthrust
- Upthrust is the force that pushes you up when floating on water.
- Upthrust is also called buoyancy.
- Saltwater is denser than freshwater.
- So floating on saltwater is easier (like the dead sea).
Sinking
- Objects will sink if their weight is greater than the upthrust.
- An object like a piece of wood floats on the ocean.
- So the wood has sunk in the air.
Ship Overload
- Ships have a large surface area to increase the upthrust.
- If the ship is overloaded with cargo, the increase in weight will make it sink.
Test yourself on Floating & Sinking
When do objects sink?
When do objects float?
Select the correct statement in each pair.
A metal block in water has a weight greater than the upthrust acting on it. What happens to the block?
A ship is slowly loaded with more and more cargo until it begins to sink. What has happened to the forces acting on it?