Forces in Fluids Chapter 11

Why don’t you sink into the snow when you wear snow shoes? Pressure` Pressure is the force pushing on a surface.

Because the size of the area over which the force is distributed has changed. Pressure = Force/Area Pressure is equal to the force exerted on a surface divided by the total area over which the force is exerted.

Units for Pressure Force is measured in Newton’s (N). Area is measured in square meters. SI unit for pressure is N/m 2 which is also called the Pascal (Pa). 1 Pa = 1N/m 2

Fluid Pressure A fluid is a substance that can easily flow. Fluids exert pressures on on surfaces they touch.

Fluids are made of molecules. Molecules are constantly moving. All of the forces exerted by the individual molecules in a fluid add together to make up the pressure exerted by the fluid.

Fluid pressure = Total force exerted by the fluid divided by the area over which the force is exerted.

Fluid Pressure all around. Air Pressure or atmospheric pressure is the pressure exerted on us by the air.

How can we support the weight of the atmosphere? Each cubic meter of air has a mass of 1 kg. How can we support this and not feel a thing? Because in a fluid that is not moving, pressure at a given point is exerted equally in all directions.

Balanced Pressures As the atmosphere is pushing down on your hand – there is also atmospheric pressure pushing up on our hand.

Remember the can crush lab?

Variations in fluid pressure Air pressure decreases as elevation increases. Remember air pressure at a certain point results from the weight of air above that point.The higher you go the less weight above you.

Why do your ears pop? As the air pressure outside your body adjusts the air pressure inside your body has to adjust too. The pressure inside is greater than outside so pressure is released and all is balanced again.

Pressure and depth Pressure increases as you descend – because there is more water above you and therefore more weight above you.