Presentation is loading. Please wait.

Presentation is loading. Please wait.

© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 37 IGCSE Physics Pressure.

Similar presentations


Presentation on theme: "© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 37 IGCSE Physics Pressure."— Presentation transcript:

1 © Boardworks Ltd of 20 © Boardworks Ltd of 37 IGCSE Physics Pressure

2 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Pressure Contents Pressure in liquids Pressure

3 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Pressure is exerted whenever a force is applied over an area. If the same force is applied in each picture, which arm exerts the highest pressure on the board? What is pressure?

4 © Boardworks Ltd of 20 © Boardworks Ltd of 37 The arm applies a force to the board via a fingertip. The force acts over a small area and so produces a high pressure. 1. High and low pressure The same force is now acting over a larger area – the palm has a greater surface area than the fingertip. A lower pressure is produced. 2.

5 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Pressure is measured in: Newtons per square metre (N/m 2 ), which are also called pascals (Pa). Pressure can also be measured in: Newtons per square millimetre (N/mm 2 ); Newtons per square centimetre (N/cm 2 ). pressure = area force P x A F Pressure is the force per unit area and is calculated using this formula: Calculating pressure

6 © Boardworks Ltd of 20 © Boardworks Ltd of 37 The same force spread over a larger area means a lower pressure. Which type of pressure? Which type of shoes would be best for walking over a muddy field – flat soles or heels?

7 © Boardworks Ltd of 20 © Boardworks Ltd of 37 The boots have flat soles and spread the person’s weight over a large surface area. These boots exert a low pressure on the ground. Which type of pressure? In contrast, the heeled shoes have a smaller surface area and so exert a higher pressure. These shoes are likely to sink into soft ground.

8 © Boardworks Ltd of 20 © Boardworks Ltd of 37 A force spread over a large area means low pressure, e.g. skis and snowboards. The large surface area of the board means the skier exerts very little pressure on the snow. This means he slides over the top of the snow and does not sink into it. Using low pressure

9 © Boardworks Ltd of 20 © Boardworks Ltd of 37 A force concentrated on a small area means high pressure, e.g. high heeled shoes, needles, ice skates, sharp knives. The narrow blade of a knife means that it exerts a high pressure and makes it easier to cut fruit and vegetables. The high pressure of the blade of an ice-skate melts the ice and helps the skater slide across the surface. Using high pressure

10 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Pressure Contents Pressure in liquids Pressure Summary activities

11 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Pressure in a liquid: acts in all directions; increases with depth. Pressure in a liquid A liquid can be used to transmit pressure from one place to another.

12 © Boardworks Ltd of 20 © Boardworks Ltd of 37 high pressure low pressure The relationship between pressure and depth is shown by a water bottle with holes along its length. Pressure (N/m 2 ) = 10 N/kg x depth (m) x density (kg/m 3 ) The pull of gravity The greater the depth, the higher the pressure The denser the liquid, the heavier it is. Pressure in a liquid

13 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Hydraulic systems use the principle that pressure is transmitted throughout a liquid. Force applied here Pressure inside all parts of the hydraulic system is the same Force transferred here Hydraulics They are used to transfer movement from one part of a machine to another without linking the parts mechanically. All hydraulic systems use two pistons linked via a pipe carrying a special oil called hydraulic fluid.

14 © Boardworks Ltd of 20 © Boardworks Ltd of 37 All hydraulic brake systems (e.g. in a car) use a small master piston and a bigger slave piston. The master piston is used to apply a force. This puts the liquid under pressure. The pressure is transmitted to the pistons on all four wheels of the car. Hydraulic brake foot pedal master piston slave pistons hydraulic fluid

15 © Boardworks Ltd of 20 © Boardworks Ltd of 37 The pressure exerted by the master piston on the hydraulic fluid can be calculated using this equation: pressure = force applied area of master piston Hydraulic brake – pressure equations The slave piston has a larger area than the master piston. So, the force exerted by the slave pistons on the brakes is greater than the force exerted by the driver on the brake pedal. The pressure is transmitted to the slave pistons and so the force exerted by the slave piston can be calculated using: pressure = force exerted area of slave piston force exerted = pressure x area of slave piston

16 © Boardworks Ltd of 20 © Boardworks Ltd of 37 The master piston of a car has an area of 5cm 2. Hydraulic brake – calculations Calculations: 1. At the master piston, P = F = 10 N = 2 N/cm 2 A 5cm 2 1. If a force of 10N is applied to the master piston, calculate the pressure created in the brake pipes. 2. At the slave piston, F = P x A = 2 N/cm 2 x 50cm 2 = 100 N So, the force exerted on the brake disc is ten times greater than the original force applied to the master piston. 2. If the slave piston has an area of 50 cm 2, calculate the force exerted on the brake disc.

17 © Boardworks Ltd of 20 © Boardworks Ltd of 37 Hydraulics activity


Download ppt "© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 37 IGCSE Physics Pressure."

Similar presentations


Ads by Google