ZIMSEC O Level Combined Science Notes: The concept of pressure
 Pressure is the force acting over an area
 In such pressure is usually the force per unit area exerted by a fluid/gas
 over a surface with which it is in contact
 \text{Pressure=} \dfrac{Force}{Area}
 If a big force is exerted over a small area it results high pressure
 An example is the force at the tip of a women’s high heeled shoes
 It is higher than the pressure exerted by flat shoes
 The pressure of high heeled shoes is even higher than that of a man wearing flat shoes
 Even when the man weighs much more than the women.
 The pressure of a stiletto is higher than that of an elephant’s foot!
 As already pointed out the formula for pressure is:
 \text{Pressure=}\dfrac{Force}{Area}
 In unit terms this can be written down as:
 \text{Pa=}\dfrac{N}{m^2}
 Pastands for pascals
 This is the unit for pressure
 Nis for newtons
 m^{2}is the area in square metres
 One Pascal is equal to 1 Newton of Pressure per square meter
 Like most units the Pascal can have prefixes such as 1 kilo pascal (1 000N/m^{2}) or even mega pascals
Example calculations
 A rectangular block with dimensions 100cm x 120 cm x 150cm and weighs 1.5 N.
What pressure does it exert: On its 100cm x 120 cm face
 100cm x 150cm face
 120 cm x 150 cm face
 Solution:

 \text{Pa=} \dfrac{1.5}{1.2}=\text{1.25 Pa}
 \text{Pa=}\dfrac{1.5}{1.5}= \text{1Pa}
 \text{Pa=}\dfrac{1.5}{1.8}=\therefore \text{0.83 Pa}

 A nail is hammered into wood using a hammer of weight 10N. If the nail has an area of 1 mm^{2} at the tip what is the pressure exerted on the wood?
 Solution:\text{Pa=}\dfrac{10N}{0.000001}\text{10000000Pa}
NB Remember to convert the square cm and square mm into square meters
To access more topics go to the Combined Science Notes page