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Unit 9L Pressure and Moments Lesson 2 Pressure. Objective: to understand that the pressure due to a force varies with the area of contact, to be able to carry out calculations for pressure. Targets: 1- 10. What is Pressure?.
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Unit 9L Pressure and Moments Lesson 2 Pressure Objective: to understand that the pressure due to a force varies with the area of contact, to be able to carry out calculations for pressure. Targets: 1-10
What is Pressure? • Pressure is, the application of continuous force by one body on another. • In other words pressure is caused by one object putting a force on another. • When you push against a wall you are applying pressure to it.
Air and Water Pressure • The atmosphere is constantly pushing down on us. • This constant push creates pressure and we call it air pressure. • Think about what happens when you fly in an airplane . What happens to your ears? Why? • The same occurs under the water as well. • Observe Water Pressure Demo • When we dive under the water the weight of the water is a force pushing on our body. • What happens as we dive deeper? • How does this pose a problem for divers and submarines.
Pressure Formula • The formula for determining pressure is: Pressure = Force/Surface Area • The unit for pressure is the Pascal and the symbol is Pa. • For the following questions find the pressure given the following forces and surface areas. • When you increase the surface area what do you do to the pressure. • When you increase the force what do you do to the pressure?
What Does Pressure Depend On • Pressure depends on surface area and force. • For example compare the surface area of the heels of these two shoes and the forces. Which would hurt more being stepped on by A or B? A B 10N 10N
What Does Pressure Depend On • Compare the surface area of the soles of these two shoes and the forces which they are exerted. Which would hurt more being stepped on by A or B? A B 10N 15N
Inverse Relationships • When we increase the surface area we decrease the pressure. • This is called an inverse relationship. • Now you know how this inverse relationship works how would you explain: • Why snowboards work? • Why sharp knives cut better than dull ones. • Imagine you are the only person around and you have to save someone who had fallen through thin ice how would you do it?
Work to Do • Read pages 126-127 • Complete questions 1-6 page 127 • Homework: • Complete Homework Sheet 10.1 and 10.2 Revision