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Pressure is defined as the force acting perpendicular to a surface per unit area.
The formula for pressure (P) is:
$$P = \frac{F}{A}$$Where:
The standard unit of pressure in the SI system is the Pascal (Pa). 1 Pa = 1 N/m2.
Other units of pressure commonly encountered include:
From the formula $P = \frac{F}{A}$, it is clear that pressure is inversely proportional to the area over which the force is applied. This means:
Example: Consider a sharp knife and a blunt knife. The same force is used to cut something, but the sharp knife concentrates the force over a smaller area, resulting in higher pressure and easier cutting. The blunt knife spreads the force over a larger area, resulting in lower pressure and more effort needed to cut.
When a person walks on a surface, the force exerted by their weight is distributed over the area of their feet. If the person wears shoes, the shoes increase the area of contact with the ground, reducing the pressure exerted on the ground. This prevents the person from sinking into soft surfaces like sand.
Table 1: Pressure exerted by different weights on a surface
| Weight (N) | Area (m2) | Pressure (Pa) |
|---|---|---|
| 100 N | 1 m2 | 100 Pa |
| 100 N | 2 m2 | 50 Pa |
| 100 N | 4 m2 | 25 Pa |
A needle has a very small area. When it is pricked against the skin, the force of the prick is concentrated over this small area, resulting in a high pressure. This high pressure causes the skin to break.
A balloon is filled with air at a certain pressure. The air inside exerts pressure on the walls of the balloon. The pressure is distributed over the entire surface area of the balloon's walls.
The pressure in the tires of a vehicle is important for its performance. Higher tire pressure means a smaller contact area with the road, leading to less rolling resistance and better fuel efficiency. However, excessively high pressure can reduce grip and cause discomfort.
Pressure in a liquid increases with depth. This is because the weight of the liquid above exerts pressure on the liquid below. The formula for pressure in a liquid is:
$$P = ρgh$$Where:
This principle is used in hydraulic systems, such as hydraulic brakes and lifts.
Pressure is a fundamental concept in physics with numerous applications in everyday life. Understanding the relationship between pressure, force, and area allows us to explain and predict phenomena ranging from walking on surfaces to the operation of complex machines.