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?