Fluids and Pressure

Fluids

• Remember that both gases and liquids are FLUIDS.

• ALSO remember that the molecules are constantly moving.

Fluids under Pressure

• All fluids exert pressure onto something.

• Pressure is the amount of force exerted on a given surface area.

• The formula is: P = F/A

Fluids and Pressure

• Pressure is measure in N/m2 more commonly known as a Pascal.

• 1 Pa = 1newton over 1 meter squared

Think About It

• Which would hurt more?• A woman stepping on your toes in sneakers or

a woman stepping on your toes in a high heal spike.

• Why?

Try Some

• If you apply a 7 N force to an area that is 3 m2 then how many Pascals do you have?

• Would the pressure go up or down if I increased the size?

Pascals Principal

• Pascal stated that a change in pressure at any point in an in closed fluid will transmit that pressure equally to all parts of the fluid.

• This means that the pressure you apply to the bottom of a tube of tooth paste must be the same pressure felt at the top of the tube of toothpaste.

Pascals Principal

• Mathematically:• P1 = P2

• Do practice on page 93.

Buoyant Force

• All fluids exert an upward force = Buoyancy

• Archimedes principal states: The buoyant force on an object in a fluid is equal to the weight of the fluid that the object displaces.

Buoyant Force

• Another way to determine if an object will float is too determine it’s density.

• Remember that Density = mass/volume.

• If an object is less dense than the liquid it is in then it will float.

Think About It

• How do large ships made of dense material stay afloat?