Hydraulics Force, Work and
Pressure. 

The force produced by a piston depends on the pressure the liquid inside the piston is under and the surface area of the piston. The force can be calculated according to the expression below. Force = pressure X area Look at the single pistons on the right. Piston "A" has a surface area of 100 cm^{2} and fluid at a pressure of 0.3N / cm^{2}. The resultant force is calculated as follows Force = 0.3N/cm^{2} X 100cm^{2} Force = 30N  
Pressure is
the force exerted per unit area. Obviously the greater the force exerted
over a small area the greater the pressure. The piston on the left has a
surface are of 100 cm^{2}and is pushed down with a force of
30 N. The pressure that the fluid inside the piston is under can be calculated
by the expression below Pressure = force / area Pressure = 30N / 100 = 0.3N/cm^{2} 

Consider carrying 25 Kg of
bricks 25 metres along the road. You can say you have done some work.
Now try carrying 25Kg of bricks 50 metres along the road. You can now
say you have done more work than before. Work
is a concept defined by the expression below. Work
= force(N) X distance(m). So the work
done on the bricks to carry them 25 metres along the road is the product
of the force, exerted by the man to lift the bricks against gravtiy and
the distance travelled. The unit for
work is the joule. One joule
of work is done when a force of one Newton is applied over a distance
of one metre. Consider the piston on the left. If a force of 3N is applied to lift an object resting on the piston 3m high the work done on the object is Work = 3N X 3m = 9Nm = 9Joules. 
