3.3 Fluids

3.3 Fluids

What are fluids?

• Liquids and gases are examples of fluids.

• Particles in a fluid can move past each other.

• Fluids exert pressure (push) evenly in all directions.

What is pressure?

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

• When you add air to a tire, you are pushing air into the tire. Inside the tire, the air molecules push against each other and against the walls of the tire.

• As you pump more air into the tire, the pressure inside the tire increases. Why?

Open Ended

Why does the pressure inside the tire increase?

Calculating pressure

• The SI unit of pressure is the pascal.

• You calculate pressure by dividing the force by the area over which the force acts.

Buoyant Force

• Buoyant force is the upward force that keeps an object immersed in or floating on a fluid.

• Archimedes' principle is used to find buoyant force. Archimedes' principle states "The buoyant force on an object in a fluid is an upward force equal to the weight of the fluid that the object displaces."

Multiple Choice

A buoyant force is a(n) ______ force 

• Upward
• Downward
• Side ways

Multiple Choice

A buoyant force is an upward force applied on an object by a 

• Substance
• Fluid
• Pressure
• Displacement

Pascal's Principle

• States that if the pressure in a container is increased at any point, the pressure increases at all points by the same amount.

Open Ended

What do the variables P, F, and A represent?

Hydraulic devices and Pascal's principle

• Hydraulic devices use liquids to transmit pressure from one point to another.

• Because these liquids cannot be compressed into a much smaller space, they can pass on pressure better than gases can.

• Hydraulic devices can multiply forces.

• Use books to look at Figure 5 (pg 92)

Multiple Choice

What is the pressure in the hydraulic fluid?

• 1210 N
• 484 N/m²
• 8000 N
• 3025 N/m²

Multiple Choice

Pressure is measured in what units

• Newtons
• m/s
• Pascals
• Moles

Multiple Choice

Look at the pressure triangle. How do we calculate the area?

• f ÷ a
• f x p
• p x f
• f ÷ p

Fluids in Motion

• Fluids in motion have some properties in common.

• Fluids move faster through small areas than through larger areas, if the overall flow rate remains the same.

• But fluids also vary in the rate at which they flow.

Viscosity

• Viscosity is a liquid's resistance to flow and it depends on the particles attracton.

• The stronger the attraction between a liquid's particles, the more viscous the liquid is.

• Example: Honey flows more slowly than lemonade because honey has a higher viscosity than lemonade.

Multiple Choice

What is viscosity?

• A liquid's resistance to flow.
• a liquids flow.
• a liquid
• gas to solid.

Multiple Choice

Peanut butter is an example of a...

• High viscosity liquid

• Low viscosity liquid

• Isnt a liquid at all! Don't be silly.

Multiple Choice

High viscosity can be described as...

• a liquid that flows quickly

• a liquid that flows slowly

Multiple Choice

Low viscosity can be described as...

• liquids that flow quickly

• liquids that flow slowly

Multiple Choice

Viscosity can be described as...

• a physical property of liquids

• a physical property of solids

• a chemical property of liquids