Calculating Pressure The Relationship between Force and Area

Calculating Pressure �Remember that force is measured in Newtons (N) and area is often measured in square metres (m 2). �The unit for pressure, therefore, is newtons per square metre (N/m 2). This unit is also called a pascal (Pa). �One pascal is a very small amount of pressure, 1 Pa=1 N/m 2. This is the equivalent of 100 grams of force spread over a 1 m by 1 m surface.

Calculating Pressure �Pressure (P) = Force (F) Area (A) or P = F A �Force= Pressure x Area= Force Pressure

Sample Problems �An aquarium is filled with water that weighs 10 000 N. If the base of the aquarium has an area of 1. 6 m 2, what pressure does the water exert on the base of the aquarium?

Sample Problems �If the atmospheric pressure is 101 200 Pa and you are holding out your hand, the atmosphere is exerting a force on your hand. If the area of the palm of your hand is 0. 006 m 2, how much force is the atmospheric pressure exerting on the palm of your hand?

Sample Problems �The weight of water in a glass is 4. 9 N. If the water is exerting a pressure of 1700 Pa on the bottom of the glass, what is the area of the bottom of the glass?

Practice – complete in notebook 1. Imagine that you are holding a lead weight on the palm of your hand. If the weight of the lead is 0. 80 N and the bottom of the weight has an area of 0. 016 m 2, what is the pressure on the palm of your hand? 2. Assume that the text book that is sitting on your desk weighs 14 N. If it has an area of 0. 60 m 2, how much pressure is the book exerting on the desk? 3. A large water jug contains water weighing 185 N. If the bottom of the jug has an area of 0. 12 m 2, how much pressure is the water exerting on the bottom of the jug?

4. The water in an aquarium exerts 2500 Pa of pressure on the bottom of the aquarium. If the area of the bottom of the aquarium is 0. 15 m 2, what force is the water exerting on the bottom of the aquarium? 5. If the air pressure generated by a nail gun is 517 k. Pa (517 000 Pa) and the area of the head of the piston that drives the nail is 5 × 10– 4 m 2 (0. 0005 m 2), what force does the air in the nail gun exert on the piston? 6. If the pressure inside a tire is 241 000 Pa, what force is exerted on every square metre of the inside wall of the tire?

7. A large stack of bricks is sitting at a building site. The total weight of the bricks is 102 000 N. If the bricks exert an average pressure of 153 000 Pa on the ground, what is the area of the ground where the bricks are stacked? 8. The water in a swimming pool weighs 24 525 000 N. If it exerts a pressure of 19 620 Pa on the bottom of the pool, what is the area of the bottom of the swimming pool? 9. A column of air from the ground to the top of the atmosphere weighs 50 662. 5 N. The air exerts 101 325 Pa on the ground. What is the area of the base of the column of air?

Complete the Following: 1. What is the formula for calculating pressure? 2. What unit is used to measure pressure? 3. What is another way to express this unit?