Chapter 17.3

• How do buoyancy and Archimedes’ principle relate to fluids?

Buoyancy

• measure of the upward pressure a fluid exerts on an object.

What is Archimedes’ principle?

• the force exerted on an object in a liquid is equal to the weight of the

fluid displaced by the object.

Example

• If a rock weighs 2.25 N using a spring scale is placed in water

• the scale will then register 1.8 N

• the water experts a force of 0.45 N

According to Archimedes’ principle the weight of the water displaced was 0.45 N

Different fluids all have different buoyancy

Why do objects sink and float?

• If the buoyancy factor is greater than the weight of the object, the object

floats.

• If the buoyancy factor is less than the weight of the object, the object

sinks.

Why does a block of steel sink, but a steel boat float?

• 1 cubic meter of water = 9,800 N

• 1 cubic meter of steel = 76,400 N

• What happens?

The block of steel is flattened and hollowed inside to make a boat,

approx. 10 cubic meters.• How much water is displaced?

• 10 cubic meters of water = 98,000 N

• 1 cubic meter of steel = 76,400 N

• What happens?

Buoyancy and gases

Charles’ law

• The volume of a gas increases with increasing temperature.

• The volume of a gas decreases with decreasing temperature.

How does Charles’ Law explain how a hot air

balloon works.

• As the air inside is heated it will become less dense than that the air

outside the balloon

Gases and pressure

What is atmospheric pressure?

• the force required to hold the air around the earth

• At the Earth’s surface the atmospheric pressure is 101,300

pascals or newtons.

Boyle’s law explains how pressure and volume are

related.

Boyle’s Law states

• 1. as the pressure of gas increases, its volume decreases

proportionately.

• 2. as the pressure of gas decreases, its volume increases proportionately.

Formula for Boyle’s law

• P1 = initial pressure V1 = initial volume

• P2 = new pressure V2 = new volume

• P1 V1 = P2 V2

Example

• Suppose 5 L of air at atmospheric pressure(101.3 Kilopascals) is

compressed in a 0.5 L aerosol can. What is the pressure of the compressed air in the can?

• Work the problem

HOMEWORK:

• Compare and contrast Charles’s law and Boyle’s Law

Viscosity of Fluids

Viscosity:

• 1. Measure of a materials resistance to flow.

• 2. Determined by the siae and shape of the molecules

Temperature and Viscosity

• As a liquid gets warmer its viscosity decreases.

• As a gas gets warmer its viscosity increases.

HOMEWORK:

• P. 307 Problems 1-3

• Honors 1-5