Home PHYSICS TOPIC 7: PRESSURE | PHYSICS FORM 1

TOPIC 7: PRESSURE | PHYSICS FORM 1

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PHYSICS FORM ONE FULL NOTES

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.

Solution

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