Pressure NotesPressure Notes

The fun never stops...The fun never stops...

Pressure in a FluidPressure in a Fluid

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

Pressure in a FluidPressure in a Fluid

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

•Liquids and Gases are fluids

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

•Liquids and Gases are fluids

Pressure in a FluidPressure in a Fluid

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

•Liquids and Gases are fluids

•Fluids exert force

•Liquids and Gases can exert forces.

– Examples: waves crashing, wind

•Liquids and Gases are fluids

•Fluids exert force

Pressure in a Fluid (cont)Pressure in a Fluid (cont)

Objects in a fluid experience a buoyant force resulting from the pressure exerted by the fluid.

Objects in a fluid experience a buoyant force resulting from the pressure exerted by the fluid.

Pressure in a Fluid (cont)Pressure in a Fluid (cont)

Objects in a fluid experience a buoyant force because of the pressure of the fluid.

Objects in a fluid experience a buoyant force because of the pressure of the fluid.

What is Pressure?What is Pressure?

• Pressure is the force per unit of area applied on the surface of an object.

• Pressure is the force per unit of area applied on the surface of an object.

What is Pressure?What is Pressure?

• Pressure is the force per unit of area applied on the surface of an object.

• Pressure depends on the force applied, and the area of contact over which the force is applied.

• Pressure is the force per unit of area applied on the surface of an object.

• Pressure depends on the force applied, and the area of contact over which the force is applied.

Calculating PressureCalculating Pressure

1 Pa = 1 N/m2

1 Pa is equal to the force of 1 Newton applied over an area of 1 m2

Pressure and Fluid HeightPressure and Fluid Height

• For any fluid, pressure depends only on the height of the column of fluid above the surface.

• For any fluid, pressure depends only on the height of the column of fluid above the surface.

Pressure and Fluid HeightPressure and Fluid Height

• For any fluid, pressure depends only on the height of the column of fluid above the surface.

• Increasing the height of the column of fluid increases the pressure.

• For any fluid, pressure depends only on the height of the column of fluid above the surface.

• Increasing the height of the column of fluid increases the pressure.

Pressure and DepthPressure and Depth• Pressure increases

with depth.• Pressure increases

with depth.

Pressure and DepthPressure and Depth• Pressure increases

with depth.

• The water column pushing down becomes taller and heavier with increasing depth.

• Pressure increases with depth.

• The water column pushing down becomes taller and heavier with increasing depth.

Pressure in All DirectionsPressure in All Directions• Fluids exert a pressure in all directions

on an object.• The pressure is perpendicular to the

surface of the object.

• Fluids exert a pressure in all directions on an object.

• The pressure is perpendicular to the surface of the object.

Atmospheric PressureAtmospheric Pressure

• Atmospheric pressure is the force exerted per unit area by air particles.

• Atmospheric pressure decreases as elevation increases.

Atmospheric Pressure Crushing things:

• http://www.youtube.com/watch?v=L2WDF1lu5Oc

• http://www.youtube.com/watch?v=gG5YmkmfCpA

• http://www.youtube.com/watch?v=Uy-SN5j1ogk

• http://www.youtube.com/watch?v=2WJVHtF8GwI

Buoyant ForceBuoyant ForceBuoyant force is the upward force on

an object in a fluid exerted by the surrounding fluid.

Buoyant force is the upward force on an object in a fluid exerted by the surrounding fluid.

Buoyant Force (cont)Buoyant Force (cont)• Buoyant force is the result of

increasing pressure at increasing depth.

• Pressure on the top of the object is less than the pressure on the bottom of the object, resulting in an unbalanced force.

• Buoyant force is the result of increasing pressure at increasing depth.

• Pressure on the top of the object is less than the pressure on the bottom of the object, resulting in an unbalanced force.

Buoyant Force and DepthBuoyant Force and Depth• The pressure exerted by a fluid

increases as depth increases.

• The buoyant force remains constant on a submerged object.

• The pressure exerted by a fluid increases as depth increases.

• The buoyant force remains constant on a submerged object.

Archimedes PrincipleArchimedes Principle• Archimedes’ principle, the buoyant

force on an object is equal to the weight of the fluid the object displaces.

• Archimedes’ principle, the buoyant force on an object is equal to the weight of the fluid the object displaces.

• The buoyant force does not depend on the object’s density or weight.

• The buoyant force does not depend on the object’s density or weight.

Sinking and FloatingSinking and Floating• If the upward

buoyant force is less than the object’s weight, the net force on the object is downward.

• If the upward buoyant force is less than the object’s weight, the net force on the object is downward.

How Can Metal Ships Float?How Can Metal Ships Float?• Overall density of the ship is less

than the density of water because a large volume of the ship is filled with air.

• Overall density of the ship is less than the density of water because a large volume of the ship is filled with air.

Floating and Sinking in the AtmosphereFloating and Sinking in the Atmosphere• Air produces a buoyant force.

• Helium balloon’s weight is less than the buoyant force.

• Air produces a buoyant force.

• Helium balloon’s weight is less than the buoyant force.

• The density of the balloon is less than the density of the surrounding air.

Floating and Sinking in the AtmosphereFloating and Sinking in the Atmosphere• Hot-air balloons float when their weight is less

than the weight of displaced air.

• Heat from the burner heats the air particles and causes them to move farther apart.

• Hot-air balloons float when their weight is less than the weight of displaced air.

• Heat from the burner heats the air particles and causes them to move farther apart.

• The density of the balloon decreases and becomes less dense than the surrounding air.

Videos• Mythbusters "Let's Talk Buoyancy"• http://science.howstuffworks.com/6540-mythbusters-lets-talk-

buoyancy-video.htm

• Mythbusters Lead balloon 5 min• http://www.youtube.com/watch?v=HZSkM-QEeUg

• Mythbusters Barrel of Bricks• http://www.youtube.com/watch?v=Vt230Pd1oSo

• Sulfur Hexafluoride Gas Boat float• http://www.youtube.com/watch?v=ckaJs_u2U_A

• Mythbusters Sulfur Hexafluoride Boat float attempt• http://www.youtube.com/watch?v=KReTvW7BTHQ