5 Pressure in a FluidThe pressure is just the weight of all the fluid above youAtmospheric pressure is just the weight of all the air above on area on the surface of the earthIn a swimming pool the pressure on your body surface is just the weight of the water above you (plus the air pressure above the water)
6 Pressure in a FluidSo, the only thing that counts in fluid pressure is the gravitational force acting on the mass ABOVE youThe deeper you go, the more weight above you and the more pressureGo to a mountaintop and the air pressure is lower
7 Pressure in a FluidPressure acts perpendicular to the surface and increases at greater depth.
9 Pascal’s Principle Pascal’s Principle pressure applied to a fluid is transmitted unchanged throughout the fluid
10 Buoyancy Net upward force is called the buoyant force!!! Easier to lift a rock in water!!
11 Displacement of WaterThe amount of water displaced is equal to the volume of the rock.
12 Archimedes’ Principle An immersed body is buoyed up by a force equal to the weight of the fluid it displaces.If the buoyant force on an object is greater than the force of gravity acting on the object, the object will floatThe apparent weight of an object in a liquid is gravitational force (weight) minus the buoyant force
13 A. Archimedes’ Principle Bouyant Forceupward force exerted by a fluid on an immersed objectbouyant force > weightballoon risesbouyant force < weightballoon sinksbouyant force = weightballoon floats
14 FlotationA floating object displaces a weight of fluid equal to its own weight.
16 GasesThe primary difference between a liquid and a gas is the distance between the moleculesIn a gas, the molecules are so widely separated, that there is little interaction between the individual moleculesIDEAL GASIndependent of what the molecules are
18 Boyle’s Law Pressure depends on density of the gas Pressure is just the force per unit area exerted by the molecules as they collide with the walls of the containerDouble the density, double the number of collisions with the wall and this doubles the pressure
19 Boyle’s Law Density is mass divided by volume. Halve the volume and you double the density and thus the pressure.
20 Boyle’s LawAt a given temperature for a given quantity of gas, the product of the pressure and the volume is a constant
21 Atmospheric Pressure Just the weight of the air above you Unlike water, the density of the air decreases with altitude since air is compressible and liquids are only very slightly compressibleAir pressure at sea level is about 105 newtons/meter2
23 Effect on Boiling Point When atmospheric pressure increases, the boiling point of a liquid increases.When atmospheric pressure decreases, the boiling point of a liquid decreases.EX: high altitude cooking, boiling cold water
24 Buoyancy in a GasAn object surrounded by air is buoyed up by a force equal to the weight of the air displaced.Exactly the same concept as buoyancy in water. Just substitute air for water in the statementIf the buoyant force is greater than the weight of the object, it will rise in the air
25 Buoyancy in a GasSince air gets less dense with altitude, the buoyant force decreases with altitude. So helium balloons don’t rise forever!!!