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Pressure

Pressure is per unit area. Pressure determines the effect of a force on a surface.

Pressure exerted by different shoes

Different styles of shoe can cause different pressures due to their area.

  • Flat shoes spread the force over a large area, reducing the pressure. Snow shoes have a much larger area than feet to spread the force over a larger area and reduce the pressure on the snow - this stops people sinking into the snow.
  • High heeled shoes transfer the force through a much smaller area, causing a much greater pressure. It will hurt more if a person steps on someone鈥檚 foot in high heels than if they were wearing flat shoes. This is also why it hurts so much to accidentally step on a plug or stones barefoot - the force acts on a small area and the pressure is increased.

Calculating pressure in fluids

Liquids and gases are . The pressure in fluids causes a force to a surface. A force that is normal to a surface acts at right angles (90掳) to it. To calculate the pressure at the surface of a fluid use the equation:

\(pressure = \frac{force~normal~to~a~surface}{area~of~that~surface}\)

\(p = \frac{F}{A}\)

This is when:

  • pressure (p) is measured in pascals (Pa)
  • force (F) is measured in newtons (N)
  • area (A) is measured in metres squared (m2)

Example

A fluid exerts a force of 50 N over an area of 2 m2. Calculate the pressure on the surface.

\(p = \frac{F}{A}\)

\(p = 50 \div 2\)

\(p = 25~Pa\)

Question

A fluid exerts a force of 150 N over an area of 1.2 m2. Calculate the pressure on the surface.