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 P 1 = initial pressure V 1 = initial volume P 2 = new pressure V 2 = new volume P 1 V 1 = P 2 V 2

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