Home PHYSICS TOPIC 7: PRESSURE | PHYSICS FORM 1

# TOPIC 7: PRESSURE | PHYSICS FORM 1

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## TOPIC 7: PRESSURE | PHYSICS FORM 1

#### Concept of Pressure

Pressure is defined as the force per unit area. OR Pressure is the force acting normally (perpendicularly) per unit surface area.

It is calculated by the formula:

Pressure = Force (f)/Area (A)
P = F/A
Where
• P – Pressure
• F – Force
• A – Area

#### The S.I Unit of Pressure

The SI unit of Pressure is Newton per square metre (N/M2). This unit is usually referred to as the Pascal (Pa).

1Pa = 1 N/M2
The other units of pressure are atmosphere, torr bar and mmHg.
• 1 atmosphere = 780mmHg
• 1 atmosphere = 1 105 N/M2 = 1bar (used by meteorologists)
Note: for a given amount of force, the smaller the area of application the greater the pressure exerted.

When a man lifts a bucket of water by its handle that is made with a thin metal, he would experience some discomfort but if the bucket was made with a thicker handle the discomfort will be much less if any.

This is because the area over which the force is applied is larger.

#### Pressure due to Solids

Dependence of Pressure on Surface of Contact

The pressure in solid depends on the surface area of contact. A force (F) applied onto a small area exerts a higher pressure as compared to when it is applied onto a large surface.

Pressure in solid = Force applied/Area of contact.

##### Example 1

A block of wood that weighs 30N and measures 5m by 10m by 4m. If it was placed on a table with the largest possible area (5mx10m) in contact with table, exerts less pressure than it would when placed with its smallest possible area (5mx4m) in contact with table.