3- Pressure

Pressure

The relationship between pressure, force and area:

  • Learn above formula by heart, if definition of pressure is asked in exam just write above formula in words as

Pressure = force / area

Theoretical understanding of the formula: If we look at the formula, the force is in numerator and area is in denominator. If force is large and area is small then the pressure would be bigger and vice versa.

As If Force = 5 N and area is 5 m2

then pressure is P= 5/5 =1 N/m or  pascal

However,

if force = 5 N and area is 0.5 m2

then pressure would be P = 5 / 0.5 = 10 N/m2

Conclusion

That is why camel can walk on the desert but a beautiful lady with a high and sharp heel can not. Reason, camel’s feet are wide so area is large and camel’s weight is divided on four legs. However, the beautiful lady’s weight is divided only on two feet and whose contact area with the ground is very small due to sharp heels.

woman heelscamel feets

Beauty does not always gives you advantage!

For further understanding, consider following 2 examples.

Example#1: An elephant weighing 40,000 N stands on one foot of area 1000 cm2 (0.1 m2). What pressure is extered on the ground?

Pressure = Force / Area                                = 40,000 /0.1      = 400,000 N/m2

Example#2: What is the pressure exerted by a girl weighing 400 N standing on one ‘stiletto’ heel of area of 1 cm2 (0.00001 m2)?

Solution:  Since Pressure = force / area  = 400 / 0.00001  = 4000000 N/m2   which is ten times bigger than elephant’s pressure on ground.

Examples, a woman having mass of 50 kg wearing a pointed heel of 0.1 cm2 would apply a pressure of 500 N; whereas, a woman having same mass wearing a heel of 0.5 cm2 would apply a pressure of 100 N. So what do you think which lady can walk easily on sand. The one with larger area of heel because smaller heel would apply more pressure and would dip deeper in sand.

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