Pressure The result of a force distributed over a given area.
Equation for Pressure:
Pressure = Force / Area
Force = Newton’s Area = m2
Units for pressure = Pascal (Pa)
Example #1 Each tile on the bottom of a swimming pool has an area of 0.50 m2. The water above each tile exerts a force of 11,000 N on each tile. How much pressure does the water exert on each tile?
Pressure = Force / Area Pressure = 11,000 N / 0.50 m2
Pressure = 22,000 Pascal's
Example #2 The weight of a gallon of milk is about 38 N. If you pour 3 gallons of milk into a container whose bottom has an area of 0.60 m2, how much pressure will the milk exert on the bottom of the container?
Pressure = Force / Area Pressure = (38 N * 3) / 0.60 m2
Pressure = 114 N / 0.60 m2
Pressure = 190 Pascal's
Two factors that affect fluid pressure:
1. Depth 2. Type of fluid
Air Pressure and the Atmosphere
Air pressure decreases as the altitude increases.
Examples:
• Ears popping while on a plane • Ears popping while diving deep in a swimming pool
Pascal’s Principle
A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.
What is a hydraulic system?
A device that uses pressurized fluid acting on pistons of different sizes to change a force.
How does a hydraulic system use fluid pressure to do work?
An increased output force is produced because a constant pressure is exerted on the larger area of the output piston.
Example
Draw this diagram:
5,000 N
Bernoulli’s Principle
As the speed of a fluid increases, the pressure within the fluid decreases.
Air always moves from higher pressure to lower pressure
How do we use Bernoulli’s principle to make planes fly (Draw diagram)?