1. Homework 4/2/2007 by 6 PM: Diagnoser Question Sets to review electricity and magnetism

2. Start reviewing for the exam

3. Riverside2 write up due 4/10/2007.

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• Drop the clay lump into the water.

• Make the clay float.

• Write down what you did to make the clay float.

Density: Engage

• Measure the densities of the marble and the wooden ball in grams per milliliter.

• Each mark on your graduated cylinder is 1 milliliter (ml). The water volume doesn’t change if you drop something into it. The water is just displaced.

• The average mass of the marbles is 5.2 grams and the wood ball is 2.7 grams.

• Why did I give you three of each?

Density: Explore

Density = Mass / Volume

• The density of water is 1 gram per milliliter.

• What is true of objects that sink in water?

• What is true of objects that float in water?

• What is the general principle?

If the density of an object is greater than the fluid it is immersed in, it will sink. Otherwise it will float.

Archimedes: The upward buoyant force on an object is equal to the volume of the fluid displaced.

Density: Explain

Real sphere of marble

Buoyant Force = Weight of fluid displaced

Gravity Force = Weight of fluid displaced

Imaginary sphere of fluid

• Often air and water can both be treated as fluids.

• Pressure is Force per Area

• Areas of high pressure push things towards areas of low pressure.

• Atmospheric pressure decreases with altitude and water pressure increases with depth.

Density: Extend

The same force applied over a smaller area results in greater pressure – think of poking a balloon with your finger and then with a needle.

• Gas molecules behave a lot like colliding billiard balls.

• Molecules in a hotter gas move faster, all else being equal.

• Increasing the temperature of a gas while keeping volume and the number of molecules constant increases the pressure.

• Increasing the number of molecules in a gas while keeping volume and temperature constant increases the pressure.

Density: Extend

• Demonstrate the Cartesian diver made from a soy sauce packet in water. You may or may not have to add a paper clip like I did. Write down your observations.

• Pass around the diver. Discuss an explanation with your groups.

Density: Evaluate