## Sunday, June 27, 2010

### form 5 chapter 3 (electromagnetism)

5 UM and 5 UKM students please download this notes.
Form 5 Chapter 3

## Tuesday, June 15, 2010

### UNDERSTANDING PRESSURE IN LIQUIDS

A liquid in a container exerts pressure because of its weight.
For example, if you try to put your finger over the end of a tap when it is turned on, you can feel the pressure of the water in the pipe.

If a fluid (liquid or gas) has a density ρ, its pressure P, at a point due to the fluid of height h, is given by
P = ρgh where g = gravitational acceleration

Therefore, for a given liquid, its pressure:
i. increases with depth
ii. increases with density

For a given point in the fluid, its pressure acts equally in all directions.
It does not depend on the shape of containers, only on its depth.

Quiz:
Example 1
If the density of sea water is 1150 kgm-3, calculate the pressure below 40m of sea water due to the water alone.

## Monday, June 14, 2010

### FORCES AND PRESSURE

Pressure is force per unit area.
The SI unit : Nm-2 = Pascal = Pa
*take note --> 1 Nm-2 = 1 Pascal

HOW DOES AREA AFFECT PRESSURE?

1. Effect of a force acting over a small area is the production of high pressure over that area.
2. Effect of a force acting over a large area is the production of a lower pressure over that area.

Applications involving High Pressure
1.A sharp knife has a very small surface area on its cutting edge so that high pressure can be exerted to cut the bread.

2.The studs on a football boot have only a small area of contact with the ground. The pressure
under the studs is high enough for them to sink into the ground, which gives extra grip.
3. Thumb tack have very sharp ends with very small surface areas. When a force is applied to the head of a thumb tack l, the pressure will drive its sharp end into a piece of paper easily.

Application involving Low Pressure
1. A tractor moving on soft ground has wide tires to reduce the pressure on the ground so that they will not sink into the ground.
2. Skis have a large area to reduce the pressure on the snow so that they do not sink in too far.
3. A wide shoulder pad of a heavy bag will reduce the pressure exerted on the shoulder of the person carrying the bag.