Edexcel GCSE Physics 1PH0
Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves
Light and the Electromagnetic Spectrum
Radioactivity
Astronomy
Energy – Forces Doing Work
Forces and Their Effects
Electricity and Circuits
Static Electricity
Magnetism and the Motor Effect
Electromagnetic Induction
Particle Model
Forces and Matter
Forces and Matter
Upthrust, floating and sinking
- 3 things to know
- Paper 2
Overview
Upthrust from the pressure difference across an immersed object, stones, helium balloons and ships, upthrust as the weight of fluid displaced with a calculation, the conditions for floating and sinking, and how fluid density affects floating.
What you need to know
Answer each one before you reveal it.
Explain why an object immersed in a liquid experiences an upward force.
Explain why a stone feels lighter to hold when it is under water.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Explain why an object immersed in a liquid experiences an upward force.
Model answer
The pressure on its lower surface is greater than the pressure on its upper surface, giving a resultant upward force.
- 2
Name the upward force that a fluid exerts on an object placed in it.
Model answer
Upthrust.
- 3
Explain why a stone feels lighter to hold when it is under water.
Model answer
Upthrust from the water acts upwards on the stone, reducing the force needed to support it.
- 4
Explain why a helium balloon rises through the air.
Model answer
The upthrust from the surrounding air is greater than the weight of the balloon.
- 5
Explain why upthrust still acts on a ship whose hull is only partly below the water surface.
Model answer
The submerged part of the hull still has water pressure pushing up on it from below.
- 6
Explain why the upthrust on an object grows as it is pushed further into a liquid until it is fully immersed.
Model answer
More of the object is surrounded by liquid, so a greater volume of liquid is pushed aside.
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