Moving Sand Cart Over a Rotating Surface

A sand-carrying cart on a track leaves a trail of sand when it travels over a rotating table. This demonstrates the Coriolis Effect.

 

The Wimshurst Machine

A Wimshurst electrostatic generator, working on the principle of induction, generates high voltage differences and sparks between two movable electrodes.   By increasing the distance between the electrodes, higher potential differences can be built up.

Electrostatic induction refers to the principle that charges in an object (especially a conductor) redistribute themselves in the presence of nearby charges. Opposite charges are attracted to each other, while similar charges are repelled. Larger charges can be stored by connecting the knobs to Leyden jars which are component parts of the machine.

 

Breakdown of Air

Grounding rod tips of different sizes are used to discharge a large Van de Graaff generator. The larger the curvature of the tip, the more charge must build up to break down the air, resulting in longer sparks.

The electricity ionizes air molecules, releasing quick flashes of light. A pointed tip barely sparks at all, but instead creates an electric field so strong that it forms a tiny ball of plasma just beyond the tip. This is known as "St. Elmo's Fire", and is just visible when all the lights are turned off.

Fluorescent and Neon Tubes in an Electric Field

A fluorescent tube swings at the end of a long plexiglass rod. It is made to rotate and then brought near the Van de Graaff generator. The tube lights up when there is a potential difference between its ends. This happens when it is pointing radially away from the Van de Graaff. The same can be done with a small neon tube.

 

Interrupted Pendulum

A pendulum swings from a support post and another post is added to interrupt its swing. We desire to know the maximum height at which the pendulum will perform a full loop around the post. The pendulum requires both potential and kinetic energy in order to complete a full loop. Therefore, it will never be able to return to its height of release while completing a full loop. Ultimately, the pendulum has enough energy to complete a full loop when interrupted at a height equal to two-fifths its initial height of release.

 

Hero's Engine

This demonstration illustrates the earliest form of steam engine, as described by Hero of Alexandria around 150 B.C. A small amount of water is heated to produce steam, which accelerates out of small tubes. In turn, the steam creates thrust and the engine quickly spins up.

 

Finding the Center of Mass...achusetts

A cutout of Massachusetts is hung in several orientations and a line is drawn straight downwards. The lines intersect at the center of mass.

 

Feather and Coin in a Vacuum

The free fall of a coin and feather are compared, first in a tube full of air and then in a vacuum. With air resistance, the feathers fall more slowly. In a vacuum, the objects fall at the same rate independent of their respective masses.

 

Double Cone and Plane

A double cone is placed on the bars of an inclined plane. Instead of rolling down the plane the cone rolls up. Although the plane slants upward, the bars diverge so that the rotational axis of the cone, which passes through the center of mass, actually moves downward.

 

Spring Paradox

A mass hangs from two identical springs. First, the springs are attached in series by a short string between them. The springs are also connected in parallel by two peripheral strings that are initially slack. The center string is cut, changing the system from series to parallel. The mass does not move downwards, as one might have thought. Rather, the mass moves upwards because the spring constant of the system is increased.

 

Michelson Interferometer

In this setup, an interferometer is used to measure the wavelength of laser light. The incident beam is split into two paths, recombined, and projected on a screen. When one of the path lengths is varied, the interference pattern on the screen changes. By measuring the distance that a path length must be changed in order to achieve the original interference pattern, one can determine the wavelength of the incident light.

 

Pulling a Cloth From Under a Beaker

A beaker is placed on top of a cloth, on top of a stool. The cloth is pulled quickly from underneath the beaker, while the beaker remains stationary. The impulse of the net force is made very small by reducing the time over which the cloth acts on the beaker. In other words, the force of the cloth does not act on the beaker long enough to accelerate it, so it does not move.

 

Plate Sliding Under a Soda Can

A can is placed on top of a metal sheet on a stool. A broom hits the sheet causing it to fly from underneath the can, while the can remains stationary. The impulse of the net force is made very small by reducing the time over which the metal sheet acts on the can. In other words, the force of the sheet does not act on the can long enough to accelerate it, so it does not move.

 

Curie Point of Iron

A piece of iron is suspended with a copper wire at the height of one pole of a magnet. At first the iron is attracted to the magnet. The iron is then heated with a torch and eventually falls from the magnet. As the iron cools it will again be attracted to the magnet.

 

Gyroscopes Made Easy

The motion of a gyroscope in response to an applied force is analyzed. TSG's gimbaled gyroscope is used to demonstrate.

 

DC Motor

A DC current is sent around a wire loop that is free to rotate. The current causes the loop to feel a torque in the presence of a magnetic field. Switching the current when the loop flips over allows it to continue accelerating, demonstrating the principle of a DC motor and the Lorentz force law.

 

Exploding Wire

A 100uF capacitor is charged to 3kV (450 joules) and then discharged through a thin iron wire, causing it to explode.

 

A Heat Gun

A small amount of water is placed inside an airtight copper tube, with the end sealed by a rubber stopper. The tube is heated using a blowtorch, causing the water inside to boil. As the water changes from a liquid to a gas the pressure inside the tube increases. Eventually the pressure blows out the stopper, blasting it across the room like a cannon.

 

Weighted Hacksaw Blade

A hacksaw blade has a weight attached to each end. The center of the blade is tightly held in a vise. The two halves of the blade then behave like coupled oscillators.

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Tuning Forks: Resonance & Beat Frequency

Two identical tuning forks and sounding boxes are placed next to one another. Striking one tuning fork will cause the other to resonate at the same frequency. When a weight is attached to one tuning fork, they are no longer identical. Thus, one will not cause the other to resonate. When two different tuning forks are struck at the same time, the interference of their pitches produces beats.

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