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2.5Unit 3: Forces, motion and pressure

Pressure between solids — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 5 of 7 1 quiz

📚 Cambridge Checkpoint Physics 0893 Hub / Topical Revision
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Lesson summary

2.5 Pressure between solids — CHECKPOINT PHYSICS 0893 notes: Explain pressure between solids and calculate pressure from force and area.Pressure = the pushing effect of a force on an areaKnife — a knife cuts because the force used causes pressure on the clayIncrease force — a big…

  • Decrease area
  • Unit with m²
  • Unit with cm²
  • Unit with mm²
  • Nails and pins
  • Scissors and knives

Part 1 of 6Pressure

Pressure
Pressure the pushing effect of a force on an area
Knife
  • Knife a knife cuts because the force used causes pressure on the clay
Increase force
  • Increase force a bigger force gives a bigger pressure
Decrease area
  • Decrease area a smaller area in contact gives a bigger pressure

Part 2 of 6Equation and units

Equation
  • Equation pressure = force ÷ area
Unit with m²
  • Unit with m² newtons per square metre (N/m²)
Unit with cm²
  • N/cm²
Unit with mm²
  • N/mm²

Part 3 of 6Small area, high pressure

Nails and pins
  • Nails and pins sharp points have a tiny area, so the pressure is high and they push in easily
Scissors and knives
  • Scissors and knives the thin cutting edge has a small area, which increases pressure
Sharp tools
  • Sharp tools a sharper knife has less area in contact with the clay

Part 4 of 6Large area, low pressure

Camel
  • Camel large feet spread the weight over a large area, lowering the pressure so it does not sink
Snow shoes
  • Snow shoes wide and flat to reduce pressure
Bed of nails
  • Bed of nails the weight acts on hundreds of nails so the pressure from each is very small

Part 5 of 6Calculating pressure

1Elephant
  • Elephant a weight of 50 000 N on a total area of 0.4 m² gives 125 000 N/m²
2Bicycle tyre
  • 500 N on a tyre area of 5 cm² gives 100 N/cm²
3Finding force
  • Finding force force = pressure × area, so 50 N/mm² on 1.5 mm² needs 75 N
4Unit of the answer
  • Unit of the answer it matches the area unit used

Part 6 of 6Investigating pressure from a foot

1Measure the mass of the person and convert to weight using weight
Measure the mass of the person and convert to weight using weight mass × strength of gravity (10 N/kg).
2
Draw round one foot on squared paper and work out the area in cm².
3
Calculate the area of both feet.
4
Calculate the pressure when standing on both feet and on one foot.
5
Repeat with the front of one foot and compare.
6
Explain that smaller area gives higher pressure.

Key terms

TermMeaning
PressureForce on a surface divided by its area.
Surface areaSize of the area in contact.
Newtons per square metreUnit of pressure, N/m².
SharpHaving a very small area at the point or edge.
WeightForce of gravity on an object.

Avoid these mistakes

1
Thinking pressure depends only on force — area is also important.
2
Using the wrong unit for pressure — it depends on the area unit used.
3
Thinking a bigger area gives a bigger pressure — a bigger area gives a smaller pressure.
4
Forgetting to share weight over all supports — divide the weight by the number of tyres or feet if needed.

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