Forces in Fluids Chapter 11 State Standard: Unbalanced forces cause changes in velocity. All objects experience a buoyant force when immersed in a fluid.

Pressure Force between two objects Two objects come into contact with each other Gravity “pulls” object down Based on area and force exerted Formula is Pressure = force ÷ Area SI unit is “pascal”

Fluid Pressure Fluid: material that easily flows – (ex. Oil, water, air) Changes shape Causes –Atoms push against each other –Pull or push –Sum of all particle forces

Air Pressure Mixture of gases in Earth’s atmosphere –Nitrogen, oxygen, argon, carbon dioxide Each cubic meter = 1 kilogram Atmospheric gases press down

Variations in Air Pressure Symptoms: ears pop, hard to breathe, cold Atmospheric pressure decreases with land elevation –Decrease in inside and outside objects –Pressure wants to balance

Measuring Air Pressure Barometer

Water Pressure Balanced pressure P exerted equally in all directions Water is 800 times denser than air P increases with depth Divers need to reach surface at slow pace or risk obtaining the bends

Density Formula is D= mass ÷ volume –Volume is the length x width x height –Volume is the amount of space an object takes up

How do you change density? Removal or adding of a fluid –Adding water increases mass (__ __ __ __) –Adding air decreases mass (__ __ __ __ __) –The larger the surface area the less P

Buoyancy Acts in the opposite the direction of the force of gravity Pushes up on an object In water, object feels lighter Submerged objects have unbalanced forces due to fluid exerting pressure on all surfaces of object/organism –Pressure increases with depth so upward pressure is greater than downward pressure

Buoyancy Video Fluids Buoyancy

Archimedes’ Principle Applies to sinking and floating objects Buoyant force acting on submerged object is equal to the weight of the volume of the liquid displaced by an object and the buoyant force.

Archimedes’ Principle Fluid air Air in container is denser than surroundings because air is under pressure (_ _ _ _) Heated air becomes less dense(_ _ _ _ _)

Pascal’s Principle Fluid exerts P on any surface it touches P increases the same amount all over the enclosed or contained fluid –Up, down and sideways

Pascal’s Principle

Bernoulli’s Principle Fluid moves from area of high pressure to low pressure Faster fluid moves the lower the pressure Moving air exerts less pressure than still air In a plane, moving air creates “lift” under plane which forces the plane up Remember “heat” increases air pressure

Bernoulli’s Principle

Application of Bernoulli’s Principle