Importance of pressure
Pressure is important in a range of everyday situations.
- 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 or boots 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 are wearing flat shoes.
- When using a sharp knife, the small area of the blade creates a large pressure, making cutting easier.
- Having caterpillar tracks on vehicles means their weight acts over a large area. This reduces the pressure they exert and are less likely to sink in to wet ground.
Question
A metal box is 60 cm long, 20 cm wide and 50 cm tall.
It has a mass of 30 kg. Find the maximum pressure which the box can exert on the top of a table.
The maximum pressure will occur when the face with minimum area is in contact with the table
The face with minimum area has dimensions 20 cm by 50 cm.
Area = 20 cm x 50 cm.
A = 1 000 cm2.
Force on the bench = weight of the box = mg.
Force = 30 kg x 10 N/kg.
Force F = 300 N.
p = \(\frac{\text{F}}{\text{A}}\)
p = \(\frac{\text{300 N}}{\text{1000 cm}^{2}}\)
p = 0.3 N/cm2
The maximum pressure exerted by the box is 0.3 N/cm2.
Question
A girl standing on one foot exerts a pressure of 6 N/cm2 on the ground. If the area of her foot is 75 cm2, calculate the downward force.
F = pA.
p = 6 N/cm2
A = 75 cm2
P = 6 N/cm2 x 75 cm2
P = 450 N.
The downward force exerted by the girl is 450 N