Physics AP Mr. Jean September 27 th, 2011

The plan: Pascal’s Law Typical AP pressure questions –A Car lift (jack) –A Pain in your ear!

Pascal Law’s: A change in the pressure applied to a fluid is transmitted undiminished to every point of the fluid and the walls of the container.

Pressure is CONSTANT! The increase in pressure is the same on the two sides of a pump. Thus a small force F 1 creates a larger force F 2. Small inputs can create large outputs!

A Car lift (jack)

A Pain in your ear! P f = Final pressure reading (Pa) P i = Initial pressure reading (Pa) ρ = density of matter (kg/m 3 ) g = gravity (m/s 2 ) h = total height (m)

Demo – Mini-jacks

Buoyant Forces:

Buoyant Force: The upwards force exerted by a fluid on any immersed object is called the buoyant force.

How to think about Buoyancy: Imagine a beach ball sized parcel of water beneath the water surface. –Since this parcel is at equilibrium the water has a buoyant force which offsets the force of gravity. –This upwards force’s magnitude is equal to the weight of the water in there parcel.

IMPORTANT FACT! The magnitude of the buoyant force on an object is always equal to the weight of the fluid displaced by the object. This is know as Archimedes’ principle.

Buoyant Force: B = p fluid gV B = buoyant force in newtons (haha Brody) p = coefficient of density of fluid. g = gravitation field (positive magnitude!) V = volume of water displaced.

Through question: You are on a boat in a lake. You have a massive steel anchor aboard. What happens with respect to the lakes water height along the shoreline when you drop the anchor in? A) The lake level gets higher with respect to the shoreline. B) The lake level remains the same... C) The lake level gets lower...

Case #1: Object Totally Submerged B = p fluid gV object F g = Mg = p obj gV object Net Force  B – F g = (p fluid + p obj )gV obj KEY POINT: The direction of motion of an object submerged in a fluid is determined only by the densities of the object and the fluid!

Case #2: Object Floating (V fluid / V obj ) = (p obj / p fluid ) This equation shows that the fraction of volume of a floating object that is below the fluid surface is equal to the ratio of the density of the object to that of the fluid.

Archimedes Crown: