Pressure Pressure: amount of force per unit of area (pressure = force ÷ area) Can change pressure by changing either the force or the area Which exerts more pressure, a pencil point or an eraser? Why?

What are some examples of pressure?

What is the best way to pull out someone from an icy pond? pressure What is the best way to pull out someone from an icy pond?

Remember air molecules are in constant motion Air Pressure Remember air molecules are in constant motion These moving molecules create air pressure Most air is close to Earth’s surface, so that is where the air pressure is greatest Less air pressure as altitude increases Air pressure is measured with a barometer

Bernoulli’s Principle: moving air exerts less pressure than still air Air pressure Bernoulli’s Principle: moving air exerts less pressure than still air Take a piece of paper and blow across it: what happens? The paper rises because the air pressure above it has decreased; pressure is higher below which pushes it up

Air Pressure Airplane wings take advantage of Bernoulli’s Principle to increase lift

Remember water molecules are more closely packed than air molecules Water pressure Remember water molecules are more closely packed than air molecules Water exerts pressure because of the weight and movement of the molecules Water pressure changes with depth more depth, more pressure Blobfish

Why are water tanks tall? Water pressure Why are water tanks tall? Water tanks are elevated so that gravity creates water pressure to push the water to homes and businesses Fluids can transfer pressure: if you apply pressure to one part of the liquid, the pressure travels throughout it Hydraulics take advantage of this

Buoyancy is the ability to float Water and other fluids exert an upwards force (buoyant force) Acts opposite to gravity Fluid pressure is exerted in all directions and increases with depth Remember submerged objects displace their own volume (Archimedes’ principle) Something floats as long as the buoyant force is equal to its weight

“Under Pressure” performed by Kermits