Notes 11-1
Pressure
What Is Pressure?
• The amount of pressure you exert depends on
the area over which you exert a force.
Calculating Pressure
Pressure = Force
Area
Area = Length x Width
Units:
Force- Newton (N)
Area-square meters (m2)
Pressure- Pascal (Pa)
Area
• The area of a surface is the number of square units that it
covers. To find the area of a rectangle, multiply its length by its
width. The area of the rectangle below is 2 cm X 3 cm, or 6
cm2.
Area
• Practice Problem
• Which has a greater area: a rectangle that is 4 cm X 20 cm or a
square that is 10 cm X 10 cm?
• The square has the greater area.
• 4 cm X 20 cm = 80 cm2
• 10 cm X 10 cm = 100 cm2
Fluids
• A material that can easily flow.
• Examples?
• Liquids
• Gases
• Tiny particles are constantly moving and colliding
with surfaces, which exerts forces on the
surfaces.
Fluid Pressure
• All of the forces exerted by the individual
particles in a fluid combine to make up the
pressure exerted by the fluid.
Air Pressure
• Right now, there is approximately 100 km of
fluid on top of you…
• AIR!
• The weight of the air exerts a force which
causes air pressure or atmospheric pressure.
• Why are you not crushed by these fluids?
• The forces are exerted from all directions so
they are balanced.
Variations in Fluid Pressure
• As your elevation
increases,
atmospheric
pressure decreases.
Variations in Fluid Pressure
• Water pressure increases as depth increases.
Measuring Pressure
• You can measure atmospheric pressure with a
barometer
• Meteorologists use barometers to measure
pressure to help forecast the weather
• Decrease in pressure = storm
Air Pressure and Altitude
• http://youtu.be/7_yf-iRf8Vc