A rope is held at the two ends so that vertical and horizontal polarized waves can be sent from one end to the other. The rope is then inserted between the two cookie coolers. When the two cookie coolers are aligned, they can pass a rope wave polarized in that direction but when they are crossed no wave can pass.

This can be used as an analogy to light waves, which are also transverse waves. Technically the mechanism of polarization in electromagnetic waves is somewhat different and more complex than this model. In an advanced class, this can be used in conjunction with Demonstration M7-01: MICROWAVES - POLARIZATION.

Pencil shaped and flat hexagonal ice crystals made of paper and foam are provided for this demonstration.

Scattering and refraction of light by these crystals creates several important natural atmospheric phenomena: (1) The sun pillar is formed by reflections of the sunlight by the flat surfaces of flat crystals when the sun is near the horizon, (2) The 22 degree halo around the moon is formed by refraction with the minimum angle of deviation from pencil ice crystals when the moon is very high in the sky, (3) The sun dog is formed to the side of the sun by refraction from flat ice crystals when the sun is low in the sky.

A slide having green and cyan segments superposed on a red background, is projected onto a screen. Chromatic aberration in the eye diffuses the boundary between any of the two pairs of colors, causing a blurry white or gray line at the boundary.

These colors were chosen because they are complements as seen by various eyes. One or both of the pairs of colors will mix to form white when viewed by virtually anyone's eyes. The colors are not quite correct in the photograph above.

Place the clean projection tray on the overhead projector with the ruler underneath. Cover the tray with a layer of water (over 1/8") and allow the water to settle. Lightly dust the surface with lycopodium powder, and adjust the projector so the powder and ruler are both in focus (center photograph). Hold the dropper just above the center of the tray and carefully release one drop of oleic acid solution onto the water surface. A circular "hole" quickly appears in the powder film, reaching its fixed maximum diameter in a few seconds (photograph at right). This is the monomolecular layer of oleic acid molecules held together by surface tension. Measure the diameter of the film so that the approximate thickness can be determined.

The following comments on the nature of oleic acid that makes this experiment possible were taken from the Science Teachers' Resource Center, Chemistry section, laboratory #31.

Molecules that are repelled by water are called hydrophobic. Molecules that are attracted to water are called hydrophilic. Cooking oil is hydrophobic; it won't mix with water. Some molecules have one end that is hydrophobic and one end that is hydrophilic. There are such molecules in the cells in your body. They are used to take hydrophobic nutrients into the cell that is mostly water. Soaps are this way also so that they can dissolve both hydrophobic and hydrophilic substances and be washed away by water.

Oleic acid is a substance with one hydrophobic and one hydrophilic end. When a small amount of oleic acid is placed on the surface of water, it stands on end with the hydrophilic end towards the water and the hydrophobic end away. If you could see them, they would look like fans at a crowded concert.

In this lab, we will find the length of one oleic acid molecule by spreading a small amount over the surface of water and measuring the diameter of the circle. The oleic acid spreads itself into a one-molecule thick layer in the shape of a VERY flat cylinder.

Read more: Determination of the Size of a Fatty Acid Molecule, by David A. Katz is a very nice article on the web describing this experiment. (pdf)

Since we cannot easily create a long duration microgravity environment in the classroom, this demonstration instead models this effect with the expansion being caused by a change in air pressure. A column of discs is separated by marshmallows, and the whole placed into a vacuum chamber. As the pressure is reduced, the gas in the marshmallows expands, forcing apart the spinal discs. When pressure returns, the spine collapses back, much like astronauts experience when they return to Earth.

Challenge your students to think of other body parts and processes that could be similarly affected by changes in gravity.

Force applied by the biceps , pulling up with the hand: Apply 2.5 kg to the biceps cable to support the unloaded forearm. The forearm may be kept at equilibrium by the simultaneous addition of masses in the ratio of 10:1 at the biceps and at the hand. The torques are balanced almost independently of the angular position of the arm.

Force applied to the triceps, pushing down with the hand: Hang the spring scale between the top hook and the hand hook, and attach the hanger to the triceps cable. Add masses to the hanger to determine how much force in the triceps is necessary to push down with the force read on the scale.