What exactly happens when the area is reduced? (forces & pressure)

  • Thread starter threy
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From what I've learnt, the pressure increases when the area is reduced. Taking the high heels as an example, the tip of high heels have a really small surface area which result in high pressure. But, in which direction does the pressure acts on? Is pressure similar to force? When the area of an object is increased, the pressure is reduced because the pressure is shared? Pressure is defined as force acting perpendicularly on per unit area, what does force per unit area mean?

I need specific answers, please help.
 

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  • #2
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But, in which direction does the pressure acts on?
Pressure is a scalar quantity. It does not have a direction.

Is pressure similar to force?
Similar how? I would say no, since one is a vector and the other a scalar.

When the area of an object is increased, the pressure is reduced because the pressure is shared?
More like force is shared over an area, loosely speaking.

Pressure is defined as force acting perpendicularly on per unit area, what does force per unit area mean?
It means just that - the amount of force that is acting on 1 square unit of Area.
 
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sophiecentaur
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From what I've learnt, the pressure increases when the area is reduced. Taking the high heels as an example, the tip of high heels have a really small surface area which result in high pressure. But, in which direction does the pressure acts on? Is pressure similar to force? When the area of an object is increased, the pressure is reduced because the pressure is shared? Pressure is defined as force acting perpendicularly on per unit area, what does force per unit area mean?

I need specific answers, please help.
The relationship between force, pressure and area is actually just a definition - which you just need to learn / remember. But it's not just arbitrary and there is a good reason why we use the two concepts, force and pressure, in different contexts.
If you think of pressure as the force being shared between the individual parts of contact area. Each of those small parts (say the surface molecules) has a certain strength to resist deformation. Increasing the area will reduce the share of the total force falling on each molecule and the deformation will be less. So it is often the pressure that determines how an object will behave, rather than the total force on it. A knife with a sharp blade will penetrate a piece of cheese but only if you use the sharp edge - same force but the area is much less along the edge.

The "perpendicular" bit in the definition is particularly relevant when we're dealing with liquids which will flow when there is a pressure difference. So there will be no tangential force when a liquid presses on a surface - only perpendicular force. It is possible for two solid objects to have other forces than just perpendicular forces between them. These are often referred to as sheer stresses and can also cause movement and deformation.
 

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