1. Module 1
FORCE

2. Examples : 1.2 PRESSURE IN FLUID SYSTEMS
Press the tube to get the toothpaste out
= PRESSURE
Uses syringe to give an injection
= uses PRESSURE

3. 1.2 PRESSURE IN FLUID SYSTEMS
Pressure Cooker
Examples :
Lifts and jacks
Bicycle Pump

4. Definition of Pressure
Pressure is defined as the force acting perpendicular to a unit surface area.
The unit of Pressure is Nm-2 (Newton per metre square) or Pa (Pascal)
Pressure (P) =
Force (F)
Area (A)
P = A F

5. Definition of Pressure
Pressure (P) =
Force (F)
Area (A)
20 N
Examples :
If the force applied is 20 N, calculate the pressure in the fluid if the surface area of the piston is m2 m2
P = A F
20 N
P = m2
= Pa

6. Exercise of Pressure
Wind blows at a pressure of 250 Pa on a wall of area 12 m2. Calculate the force acting on the wall.
P = A F
Force, F = PA
F = 250 Nm‾² x 12 m2
F = N

7. Atmospheric Pressure
Layer of air
Exert pressure

8. Example of Atmospheric Pressure
The upward pressure of the air (atmosphere) on the cardboard is strong enough to support the weight of the water in the glass.

9. Examples of the Use of Atmospheric Pressure
Drinking Straw
Plunger
Rubber Sucker
Siphon

10. Drinking Straw
Atmospheric pressure
Low pressure at the end of the straw
Atmospheric pressure acting on the surface of the water will push the water up the straw and into our mouths.

11. Atmospheric Pressure outside - HIGH
Rubber Sucker
Atmospheric Pressure outside - HIGH
Partial vacuum
Made to stick on to a smooth wall such as glass or tiled wall.
Pressed it against the glass sheet, air will be forced out.
Pressure inside - LOW
Thus, a rubber sucker can be used for hanging objects from a wall

12. Siphon Uses : To draw out liquid from a container
Consists of a rubber tube
When one end of the tube is sucked, a low pressure is created at the end.
Uses : To draw out liquid from a container
Atmospheric pressure acting on the surface of liquid in the container will than be at a higher pressure than the other end.