LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END COMPUTER PRESENTATIONS FOR KS3 SCIENCE - PHYSICS ©2003, STEVE PARKER COMPUTER PRESENTATIONS FOR KS3 SCIENCE - PHYSICS ©2003, STEVE PARKER

1 1 KS3 SCIENCE - PHYSICS KS3 SCIENCE - PHYSICS Pressure

PRESSURE ON SURFACES 2 2

3 3 Pressure tells us how spread out or concentrated a force is over an area Pressure tells us how spread out or concentrated a force is over an area Pressure = Force Area with the answer in Newtons per square metre (1 N/m 2 = 1 Pascal) Pressure = Force Area with the answer in Newtons per square metre (1 N/m 2 = 1 Pascal)

PRESSURE ON SURFACES 4 4 What would happen to this skier if she wore pointed heels on the snow? What would happen to this skier if she wore pointed heels on the snow?

5 5 PRESSURE ON SURFACES Materials can only stand a certain amount of pressure before they give way Materials can only stand a certain amount of pressure before they give way

PRESSURE ON SURFACES 6 6 A certain force concentrated on a small area creates much more pressure than the same force spread over a big area A certain force concentrated on a small area creates much more pressure than the same force spread over a big area

PRESSURE ON SURFACES 7 7 A certain force concentrated on a small area creates much more pressure than the same force spread over a big area A certain force concentrated on a small area creates much more pressure than the same force spread over a big area So sharp things tend to sink in So sharp things tend to sink in

PRESSURE IN LIQUIDS 8 8

9 9 Pressure in liquids acts in all directions Pressure in liquids acts in all directions

PRESSURE IN LIQUIDS 10 Pressure increases with depth, because there is more weight of liquid above Pressure increases with depth, because there is more weight of liquid above

PRESSURE IN LIQUIDS 11 This is why dams are wider at the bottom than the top This is why dams are wider at the bottom than the top

PRESSURE IN LIQUIDS 12 The “Density” of the liquid (the weight per litre) also affects pressure The “Density” of the liquid (the weight per litre) also affects pressure E.g. liquid mercury is more dense than water so the pressure inside is greater E.g. liquid mercury is more dense than water so the pressure inside is greater

ATMOSPHERIC PRESSURE 13

ATMOSPHERIC PRESSURE 14 The atmosphere is made up of gases, which like liquids exert pressure in all directions, including up The atmosphere is made up of gases, which like liquids exert pressure in all directions, including up

ATMOSPHERIC PRESSURE 15 Normal atmospheric pressure is enough to hold up 760 mm of mercury Normal atmospheric pressure is enough to hold up 760 mm of mercury 760 mm

ATMOSPHERIC PRESSURE 16 The weight of the atmosphere pushes the mercury down and into the tube The weight of the atmosphere pushes the mercury down and into the tube 760 mm Pressure

ATMOSPHERIC PRESSURE 17 Aircraft have wings rounded on top and flatter underneath, so the air has further to travel above the wing than it does below the wing Aircraft have wings rounded on top and flatter underneath, so the air has further to travel above the wing than it does below the wing

ATMOSPHERIC PRESSURE 18 This means the air above the wing has to travel faster than the air below the wing and it thins out, becoming less dense This means the air above the wing has to travel faster than the air below the wing and it thins out, becoming less dense

ATMOSPHERIC PRESSURE 19 Low pressure area above wing Low pressure area above wing This means the air above the wing has to travel faster than the air below the wing and it thins out, becoming less dense This means the air above the wing has to travel faster than the air below the wing and it thins out, becoming less dense

ATMOSPHERIC PRESSURE 20 Low pressure area above wing Low pressure area above wing Atmospheric pressure from below wing creates “Lift” Atmospheric pressure from below wing creates “Lift”

ATMOSPHERIC PRESSURE 21 Any correctly shaped craft will experience lift if it can cut through the air - this includes gliders Any correctly shaped craft will experience lift if it can cut through the air - this includes gliders