Re: what is the difference between pressure and force?

Jessica,

Force and pressure are related to one another, but are definitely different 
things. I'll try and clear things up for you.

A force is an application of energy that tries to make something change its 
motion. A good example of this is when you put a ball on a level floor and 
give it a push. The push applies a force to the ball, which then changes 
from not moving to rolling across the floor. To stop the ball, you would 
apply a force in the opposite direction and make it come to rest.

Sometimes a force doesn't make something move because it's exactly matched 
by an opposite force. When you sit on a chair, your weight is a force 
acting on the chair: the chair pushes back just as hard onto you, so you 
don't fall through the chair. The two forces (your weight and the chair's 
pushing back) balance out.The units of force are pounds (in the US) or 
Newtons (in the Metric system) 

Pressure is a force spread out over an area that it acts upon. For example, 
lets say I was walking along and I stepped onto a one-inch square piece of 
brick on the sidewalk. I weigh around 175 pounds, so my body would apply a 
175 pound force to that piece of brick. The sidewalk would also feel that 
force transmitted through the piece of brick, spread out over the one 
square inch of surface the brick has in contact with the sidewalk. The 
pressure is the force divided by the area it acts on (P = Force/Area), so 
in this case the pressure applied to the sidewalk is 175 pounds per square 
inch. If that piece of brick were 5 inches square, its area would be 25 
square inches: the pressure applied to the sidewalk would be 175 pounds/25 
square inches = 7 pounds per square inch. The same force is acting on the 
sidewalk: it's just spread out over more brick surface. Pressures can have 
units of pounds per square inch, or Newtons per square meter (called 
Pascals).

Liquids also have pressure which depend on their weight, how closely packed 
their molecules are, and their temperature. This pressure is caused by the 
molecules of the liquid bouncing agains a surface they're in contact with - 
like the inside of a jar, or the inner surface of an eye. If a liquid has a 
pressure of one pound per square inch, every square inch of surface it 
presses against has one pound of force spread over it. 

The total amount of force the pressure exerts on the surface is found by 
multiplying the pressure by the area of the surface it is pushing on (F = 
Pressure x Area).  The one pound per square inch from before pushing on ten 
square inches of surface adds up to a total force of ten pounds trying to 
push whatever the surface is attached to. 

So, a force is essentially a push, and pressure is a push spread out over a 
surface.

I hope this is helpful.