S3.7.7 For the adult
Pressure
Why does a sharp knife cut, when a blunt one only squashes?
What this chapter teaches
Pressure is force divided by area. The same force on a smaller area gives a bigger pressure, which is why a knife cuts and why wide feet stop a camel sinking in sand.
Three questions to ask
There is no one right wording. Listen for the idea.
- A push of 24 newtons is on 3 square centimetres. What is the pressure?
- Why does a wide foot sink less in sand than a narrow one?
- Is a bigger force always a bigger pressure? Why not?
After the chapter, the learner can
- Calculate pressure as force divided by area
- Explain why sharp knives cut and wide feet stop camels sinking in sand
What they copy into their notebook
Pressure = force ÷ area, in N/cm². The same force on a smaller area gives a bigger pressure. Sharp edges cut. Wide feet spread weight out.