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Force and Pressure

We often see person lifting box, hitting rock, pulling door, pushing another man, shutting door, opening book, kicking foot ball, picking object, sitting on chair, sleeping on the lane. These all gives some kind of push or pull in motion where force as well as pressure acts. We could even see when two bodies interact a force come to play and there could even be the change in the direction of motion. 

Force and Pressure are the concepts acting simultaneously on the body in motion. The force is nothing but the interaction between any two bodies or the push or pull between them while the pressure tells how much is the push or pull the body experiences when force is applied over a particular area. Lets see more about force and pressure in this page.

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Force Definition

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Force is the push or pull the body undergoes when two bodies undergo interaction with each other. Once this interaction stops there would be no more acting.The force is hence defined as the physical cause that changes or tends to change the dimensions or the state of rest or the state of motion of a body. The Force formula is given by
F = maWhere m is mass of the body, a is the acceleration with which the mass accelerates

Effects of Force

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The effect of force is expressed by the Newton's second law which tells the rate of change of momentum increases as the force applied is increased. Here we can see the two force effects:
  • When certain number of forces act on a body in the same direction the effect would be the same in that direction. This is what we call as Resultant force.If a rock is stuck some where in between road and some boys push it with enough force the resultant force would be the sum of the forces the boys have applied.
  • Balanced forces are said to be acting if we could see the body doesn't change its states of motion even as the forces applied cancel out. Suppose two boys are pushing a table standing in opposite direction applying equal force the forces get balanced and net resultant force is zero.

Types of Forces

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There are basically two types of force - Contact force and Non contact force. The forces that act on the bodies that are in physical contact are known as contact forces whereas the forces which act on bodies without being in any physical contact are Non contact forces. Frictional force, Spring force, tension force, normal force, air resistance force, applied force are all contact force while gravitational force, electric force, magnetic force are all Non contact forces.

Pressure Definition

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Many often get confused that force and pressure are same, but no so! Pressure is the force the body exerts per unit area. If certain force say 1 Newton acts over a contact area of 1 square meter, then the pressure over this area is 1 newton per square meter (N/m2). The relationship between force and pressure is given by
P = $\frac{F}{A}$Where F is the force acting over the area A.

Some examples on Pressure are the railway track are laid on large sized wooden, iron or cement sleepers, tractors having widened tires, the school bags provided with wide stripes.

Force and Pressure Examples

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Lets see some examples on force and Pressure:
Example 1:

A force of 1200 N acts on the surface of area 10 cm2 normally. What would be the thrust and pressure on the surface?

Given:


Force F = 1200 N, Area A = 10 cm2 = 10 $\times$ 10-4 m2 = 10-3 m2

Thrust = Normal pressure = F = 1200 N

$\therefore$ Pressure P = $\frac{F}{A}$ = $\frac{1200 N}{10^{-3} m^2}$
              
                      = 1.2 $\times$ 106 N/m2
Example 2:

The elephant weighs 20,000 N stands on one foot of area 1000 cm2. How much pressure would it exert on the ground?

Given:


Force applied by elephant F = 20,000 N, area A = 1000 cm2 = $\frac{1000}{100 \times 100}$ m2 = 0.1 m2

The pressure is given by

Pressure P = $\frac{F}{A}$
                 
                 = $\frac{20,000 N}{0.1 m^2}$
                
                 = 2,00,000 N/m2.

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