Pressure

Force (N)

Area (m2)Pressure =

The amount of force applied per unit area on an object’s surface

The unit for pressure is the Pascal (Pa)

1Pa = 1 N/m2

Or P = F/A

1kPa = 1,000 Pa

A water glass sitting on a table weighs 4N. The bottom of the water glass has a surface area of 0.003 m2. How much pressure does the water glass exert on the table?

Pressure

P = F/A »

4N ÷ 0.003m2 = 1,333 Pa

Pressure

P = F/A »

600N ÷ 0.012m2 = 50,000 Pa

A student weighs 600 N. The student’s shoes are in contact with the floor over a surface area of 0.012 m2. Calculate the pressure exerted by the student on the floor.

Pressure

P = F/A »

3,000N ÷ 2 m2 = 1,500 Pa

What is the pressure exerted by a 3,000 N crate that has an area of 2 m2?

PressureWhat is the weight of a rock that has an area of 10 m2 and that exerts a pressure of 250 Pa?

P = F/A » (manipulate formula) » F = P x A

250Nm2

10 m2 X = 2,500 N

Pressure

P = F/A » (manipulate formula) » A = F/P

A box that weighs 250 N is at rest on the floor. If the pressure exerted by the box on the floor is 25,000 Pa, over what area is the box in contact with the floor?

250N25,000 N

1 m2 X = 0.01 m2

Fluid Pressure

A fluid is any substance that has no definite shape and can flow.

What is a fluid?

Pressure in fluids.

• The height/depth of the fluid helps determine the pressure in the

fluid

• Pressure in fluids increases with depth.

• Fluids exert pressure in all directions on an object.

Atmospheric Pressure

A unit of pressure equal to the air pressure at sea level. It equals the amount of pressure that will support a column of mercury 760 millimeters high at 0 degrees Celsius under standard gravity, or 14.7 pounds per square inch (101,325 Pa).

What is an “Atmosphere”?

In other words:

1atm = 101,325 Pa

Atmospheric PressureMount Everest has been shown to be 29,028 feet high. The summit of Mount Everest has an average pressure around 30 kPa (30,000 Pa). Atmospheric pressure at sea level is 101,325 Pa.

Why is pressure on top of Mount Everest a factor for mountaineers to consider before they embark on an adventure of a lifetime?

Because so few climbers would be able to reach the summit by breathing natural air

No one knows that exact depth and pressure the human body can withstand while scuba diving, but it is deeper than 1,500 feet (457 meters). No one is going to reach that depth while scuba diving because of various symptoms. Beyond 100 feet (30 meters), nitrogen narcosis affects someone's ability to think and at 150 feet (46 meters), they may become dizzy. Once a diver reaches 250+ feet (76+ meters), they are considered useless and become a safety hazard to themselves and people around them.

The record of deepest SCUBA dive is currently held by Mark Ellyatt of 313 meters (1,027 feet) which was set on December 18, 2003.

This was a pressure of 3,256,686.34 pa or 472.34 psi

Atmospheric Pressure

1. 0.5m of water in a large fish tank exerts ____ 0.5 m of water in a swimming pool.

More pressure on the bottom than

Less pressure on the bottom than

The same pressure on the bottom as

Can’t determine

Questions:

Atmospheric PressureQuestions:2.The Pascal is equal to _____________ of force

applied over an area of ____________.

Two Newtons; Two Meters

One Newton, One Square Meter

One Kilogram; One Square Meter

Two Kilograms; Two Meters

Atmospheric PressureQuestions:3. In what direction is fluid pressure always directed

4.What would happen if astronauts, who wear pressurized suits, took their suits off?

5.Why don’t you notice atmospheric pressure on your body?

6.An aluminum can is heated causing the air particles inside to become further apart from each other. The can’s opening is quickly sealed. What will happen to the can as it cools?

Atmospheric PressureQuestions:7. In what direction is fluid pressure always directed

8.What is the SI unit for pressure?

9.Of the following choices, where would atmospheric pressure be the greatest?

Altitude at which planes fly

On a mountain top

At sea level

Below Sea level

Atmospheric PressureQuestions:10.A 30 kg box is 0.2 m long and 0.15 m wide. What

pressure does it exert on the floor?

11.Why are cabins of jet planes pressurized?