Presentations

Special Bouncing Collisions

Same as previous except that mass ratio of balls is 1:3 (softball:basketball) leaving basketball dead and softball four times the height.

tennis and basketball

Double Bubble

What it shows

When two different size soap bubbles are connected together, the smaller diameter bubble will shrink and collapse to blow up the larger diameter bubble. One can use this to demonstrate Laplace's law or the phenomenon of minimizing the surface area of a soap film.

How it works

Laplace's law tells us that the gauge pressure of a spherical membrane is given by 2γ/r, where γ is the surface tension and r is the radius of the sphere.1 For soap bubbles (which have an inside as well as outside surface), the gauge pressure is twice...

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Circular Motion and Simple Harmonic Motion

Simultaneous shadow projection of circular motion and bouncing weight on spring.

What It Shows

One of the simplest of periodic motions is uniform circular motion. By shadow projecting both uniform circular motion and oscillatory simple harmonic motion onto a screen, one can show that these two seemingly different kinds of motion are actually identical.

How It Works

A 8 cm diameter plastic ball mounted near the edge of a 46 cm diameter disk undergoes uniform circular motion. The disk, oriented vertically, is driven by a 57 RPM motor.1 A large...

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Inverted Pendulum

A physical pendulum finds stability in its inverted position when driven at the proper frequency and amplitude combination.

How it works

The physical pendulum is a 45 cm x 2 cm x 6 mm (1/4") strip mounted on a ball-bearing pivot and can rotate 360 degrees. Its pivot is driven by a 3/4" stroke Sears Craftsman Auto Scroller Saw (...

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Acoustic Horn

What it shows:

As a passive amplification device, the exponential horn is amazing. Using a "talking" greeting card as a feeble source of music, the intensity of the sound gets amplified by about 18 dB when the greeting card is coupled to the horn ... a dramatic effect.

How it works:

The multicellular horn is a cluster of eight smaller exponential horns, each with a small mouth to avoid beaming in a large frequency range, but together they form a sector of a sphere large enough to control directivity at low frequencies — the...

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Induced Electric Dipole

What it shows:

Bringing a charged rod close to neutral dielectric polarizes the dielectric's surface charges. Here a pile of Styrofoam puffs are polarized and attracted to a charged rod.

How it works:

The neutral puff experiences a non-uniform electric field from the rod. Although there are polarized charges of both kinds, because (figure 1) the field is stronger near the rod due to the concentration of positive charges, there is a net attraction. On a dry day they'll jump to meet the rod.

figure 1....

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Hand Battery

Copper and zinc plates connected by micro-ammeter; your hand completes the circuit.

Clean copper and zinc sheet metal stock is cut into strips or pads. Alligator clip a zinc strip and a copper strip and plug the leads into a modern multimeter. DC 2V scale should cover the 1.09V that we expect from a zinc/copper battery at standard conditions of 1 Molar electrolyte and room temperature.

Our fingers are a network of electrolytic conductors, with more or less conductance (depending on moisture and salt). Pressed to the metal strips, adjacent fingers complete the circuit and...

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Magnetic Bubbles

What it shows:

A thin wafer of Ferromagnetic Garnet reveals its magnetic domain alignment as light and dark serpentine patterns when viewed between crossed Polarizers. These domains can be flipped by an external magnetic field, changing the pattern structure.

How it works:

The magnetic bubble apparatus consists 1 of a thin (8-12μm) single crystal film of Ferromagnetic Garnet (FMG) sandwiched between a pair of crossed Polaroids. The FMG crystals are magnetically anisotropic, that is, they have a strong tendency to orient...

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