Physics Demonstrations, Lusk, WY, April 18, 2011

Preliminary list for grades K-2: There will be a few changes, some items will be dropped due to time constraints. If topics are important to your curriculum let me know.

This activity is in collaboration with:

National Security Technologies, Los Alamos Operations
The Bradbury Science Museum, Los Alamos National Laboratory

with support from:
Casper Fire Extinguisher

1 Geysers

The model of a Geysers shows that a geyser requires a unique structure as well as a heat source. The restricted pipe upward prevents heat transfer through convection. The weight of the column of water increases the pressure at the bottom of the column increasing the boiling point of water. Once the water starts to boil, the hot steam moving upward lowers the pressure at the bottom since steam has a much lower density than water. With lower pressure, the boiling point falls and the water quickly evaporates creating the eruption. Evaporation cools the bulk of the water and the process starts again.

2 Mass and Inertia – Newton’s First Law

Objects at rest remain at rest unless acted on by a net force. The glasses stay in place when the tablecloth is pulled due to their inertia. If the glasses were empty they would be more likely to move since they would have less mass and therefore less inertia.

3 Centripetal Force – Newton’s First Law

Objects in motion will continue to move in a straight line unless acted upon by a force. The water in the bucket tends to move in a straight line. We must apply a force (centripetal force) to keep it moving in a circle. In the case of orbits (satellites, the Moon, planets) the centripetal force is provided by gravity.

4 Newton’s Second Law (F=ma)

Force = mass x acceleration. The firecrackers apply the same force to both cans but the less massive can has a greater acceleration, reaches a greater speed, and therefore flies to a greater height than the more massive can. The less massive can is not always obvious. Extra metal was added to one can making it about twice the mass of the unaltered can, pointing out the importance of have complete information before making predictions.

5 Action/Reaction – Newton’s Third Law

For every action there is an equal and opposite reaction. The pressure in the tank (approx. 800 psi) forces the CO2 out of the modified fire extinguisher, the reaction is an equal but opposite force accelerating the passenger. The same principle explains the thrust provided by rockets for use in the atmosphere or in space. (Conservation of momentum can also be used to describe this demonstration.)

6 Conservation of Energy

Conservation of energy is shown using a pendulum made from a bowling ball suspended by a rope. When the bowling ball is pulled back against the demonstrator’s nose all of the energy is Potential Energy. At the bottom of the swing all of the Potential Energy (PE) is converted to Kinetic Energy (KE). The total energy is conserved (remains constant) and can only be transferred from between KE and PE so the demonstrator’s nose is safe; the bowling ball cannot return to a greater height than it started.

7 Angular Momentum

Show that the effect of gravity on the motion of a gyroscope (spinning bicycle wheel) depends on the initial rotation. Gyroscopes are used to maintain stable orbits of spacecraft such as the International Space Station.

8 Electrostatics

Use the Van De Graff generator to show various aspects of electrostatics including making a person’s hair stand out. (Opposite charges attract, like charges repel.) It is important to note that no charges are created, charges are only moved. Charge conservation says charge cannot be created or destroyed; as the sphere acquires a negative charge the base acquires an equal positive charge.

9 Polarization of Light

The first polarizing filter passes light with the the waves polarized in one direction. The corns syrup rotates the polarization direction different amounts for each color so each color show up a different angle when viewed with the second polarizer.

10 Total Internal Reflection

Demonstrate the concept of fiber optics work by observing a laser beam following a stream of water. Similar to the lens, the beam of light changes direction at the water/air interface. Due to the difference in the speed of light in air relative to water, all of the light energy is reflected back into the water.

11 Pressure (= Force Area)

Pressure and force are related but it is important to understand the distinction. A person can lie on a bed of nails because their weight (the force of gravity pulling them down) is distributed over a large enough area; the pressure is low enough that the skin is not damaged.

12 Atmospheric Pressure

Adding up the contribution of the weight of the entire atmosphere (greater than 50 miles in height) leads to a substantial total weight which we measure as atmospheric pressure. Atmospheric pressure is 14.7 psi at sea level, but only about 12 psi (engineeringtoolbox.com) at the altitude of Lusk. The volume of a balloon or of shaving cream changes dramatically as the surrounding pressure is reduced.

13 Bernoulli Effect

Make a screwdriver “float” in front of class. Just like an airplane wing, the pressure is lower above the screwdriver because the air is moving faster.

14 Thermal Expansion

As the air in a balloon is cooled in liquid nitrogen it contracts and eventually turns to liquid because of the low temperature. The properties of materials, such as a racquet ball, change greatly at low temperatures. The temperature of liquid nitrogen is similar to the temperature near the surface of Jupiter or Saturn which shows one of the challenges of building spacecraft to withstand the hostile environment of space.

15 Ping Pong Bazooka

We usually think of energy being stored in a pressurized container, but energy is also stored when pumping the air out of a container to create a vacuum. Energy = Work =Force x Distance, to pump air out of the cylinder we apply a force acting over the distance the air must travel to be pumped out. The bazooka’s vacuum cylinder is sealed on both ends by a thin membrane of aluminum foil. When the foil on one side fails, the air rushing in to return to equilibrium creates a shock wave and the ping pong ball is carried by this wave to a high speed as shown by the damage it can do.