AQA GCSE Physics
AQA GCSE Physics 4.5.5.1 Pressure in a Fluid Exam Questions
Free AQA GCSE Physics exam questions for 4.5.5.1 Pressure in a Fluid, with a mark scheme for every pack. Covers fluid pressure, p = F/A, pressure at right angles to surfaces, pressure due to a liquid column, upthrust and floating.
4.5.5.1 Pressure in a Fluid exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Physics 4.5.5.1 Pressure in a Fluid
Pressure in a fluid is a physics only section of AQA GCSE Physics, examined on Paper 2. All physics students need to know that a fluid exerts pressure at right angles to any surface and use p = F / A. Higher tier only content includes the pressure due to a column of liquid, p = h ρ g, why pressure increases with depth, upthrust, and why some objects float while others sink. Examiners test calculations with area conversions and explanations of upthrust using the difference in pressure on the top and bottom of an object.
What you need to know
- Pressure in fluids A fluid can be either a liquid or a gas. The pressure in fluids causes a force normal (at right angles) to any surface.
- p = F / A Pressure = force normal to a surface / area of that surface. p = F / A, with p in pascals (Pa), F in N and A in m^2. 1 Pa = 1 N/m^2. This must be memorised.
- Column of liquid (Higher tier only) p = h ρ g, where h is the height (depth) of the column in m, ρ is the density of the liquid in kg/m^3 and g is gravitational field strength. This is on the equation sheet.
- Pressure and depth (Higher tier only) Pressure increases with depth because there is a greater weight of liquid above that point. A denser liquid also gives a greater pressure at the same depth.
- Upthrust (Higher tier only) An object partially or totally submerged experiences a greater pressure on its bottom surface than on its top surface. This creates a resultant upward force called upthrust.
- Floating and sinking (Higher tier only) An object floats if its weight equals the upthrust, which happens when it is less dense than the fluid. If its weight is greater than the maximum upthrust, it sinks.
Common mistakes in 4.5.5.1 Pressure in a Fluid
- Leaving area in cm^2. Convert to m^2 by dividing by 10 000 before using p = F / A.
- Saying pressure acts only downwards. In a fluid it acts in all directions, at right angles to surfaces.
- Explaining upthrust as 'the water pushing up' without mentioning the pressure difference between the top and bottom surfaces.
- Using mass in p = F / A. Use weight (force) in newtons.
Try three 4.5.5.1 Pressure in a Fluid exam-style questions
1. A box weighing 600 N rests on the ground on a base of area 0.30 m^2. Calculate the pressure it exerts. (2 marks)
Show the mark scheme answer
p = F / A = 600 / 0.30; = 2000 Pa.
2. Higher tier: Calculate the pressure due to water at a depth of 4.0 m. Density of water = 1000 kg/m^3, g = 9.8 N/kg. (2 marks)
Show the mark scheme answer
p = h ρ g = 4.0 x 1000 x 9.8; = 39 200 Pa.
3. Higher tier: Explain why an object submerged in water experiences upthrust. (3 marks)
Show the mark scheme answer
Pressure increases with depth; so the pressure on the bottom surface is greater than on the top surface; this gives a larger upward force than downward force, a resultant upward force (upthrust).
4.5.5.1 Pressure in a Fluid FAQs
What does AQA GCSE Physics 4.5.5.1 Pressure in a fluid cover?
It covers pressure acting at right angles to surfaces, p = F / A and, for Higher tier, p = h ρ g, pressure increasing with depth, upthrust and floating.
Is pressure in fluids physics only?
Yes. The whole of 4.5.5 is physics only, and the column of liquid, upthrust and floating content is also Higher tier only.
What units should I use for pressure?
Use pascals (Pa), with force in newtons and area in square metres. Watch for areas given in cm^2 and convert them to m^2.
