Presentations

Earth's Magnetic Field

OHP representation of lines of force using bar magnet and iron filings.

What it shows:

The magnetic field lines of the Earth can be represented by the field lines of a bar magnet.

How it works:

The Earth's magnetic field is basically a magnetic dipole. It can therefore be represented to first approximation by the field of a bar magnet. The shape of the field lines can be highlighted by the sprinkling of iron filings, or by the use of plotting compasses. The latter method has the advantage of showing the variation of dip...

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Reaction of Hydrogen and Oxygen

Blue balloon with hydrogen, green balloon with helium, red balloon in back with hydrogen and oxygen mixture, and, on a cart, a red water balloon on large watch glass. Candle on a stick with matches, and a needle in the end to prick the water balloon.

Safety glasses and hearing protection is required for the demonstrator and anyone else who can't cover their ears for the red balloon.

Bernoulli Wind Tunnel

What it shows

Bernoulli's Principle states that the pressure exerted by a fluid is velocity dependent; the faster the velocity the lower the pressure. This can be demonstrated by a form of Venturi tube, a pipe with a narrow constriction which forces an increase in fluid velocity.

How it works

The varying cross-section of the wind tunnel forces air to travel its length at different velocities, with the highest velocity being at its most constricted part. From equipartition of energy, the increased energy in one degree of freedom (the kinetic energy of the flow)...

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Shoot-n-Catch

Ball shot up from PASCO cart is caught by same; a puzzler to ponder if track is tilted and cart accelerates down (or decelerates up).

shoot-n-catch

Friction Blocks

Selection of blocks that slide down a variable-angle inclined plane to demonstrate the various aspects of friction.

What it shows:

There are actually three (or more) demonstrations under the wing of this title: (1) A block or box is placed on an adjustable inclined plane which can be raised until the block slides. The tangent of the angle then gives the coefficient of friction between the surfaces. (2) The difference between dynamic and static friction may be demonstrated. A large dial spring balance is used to determine the forces required to drag a box on...

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Falling Faster than 'g'

What it shows:

Allow a board to rotate under the force of gravity and the free end will accelerate at a rate greater than g. Relation between angular acceleration and linear acceleration seems to give free-fall paradox.

How it works:

If a board, held in a vertical position with one end resting on the...

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Loop-the-loop

A toy car rolling down a loop-the-loop track demonstrates the minimum height it must start at to successfully negotiate the loop.

What it shows:

For an object to move in a vertical circle, its velocity must exceed a critical value vc=(Rg)1/2, where R is the radius of the circle and g the acceleration due to gravity. This ensures that, at the top of the loop, the centripetal force balances the body's weight. This can be shown using a toy car on a looped track.

How it works:

The car is released from the top of a ramp and runs down a slope towards...

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Parallel-Axis Theorem

What it shows:

One can show that the period of oscillation of an object doesn't change for different suspension points, as long as they're the same distance from the COM. This is consistent with what the parallel-axis theorem tells us about the moment of inertia of the object.

How it works:

The parallel-axis theorm states that if Icm is the moment-of-inertia of an object about an axis through its center-of-mass, then I, the moment of inertia about any axis parallel to that first one is given by I = Icm +...

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Spiral Fracture

What it shows:

A spiral fracture is incurred when a torque is directed along the axis of a limb or shaft. Planes perpendicular to the axis are unaffected, but those parallel are twisted, which causes pure tensile forces in one part of the limb, pure compressive forces in another. Fracture occurs when either the compressive or tensile limit of the material is exceeded. This demo shows a spiral fracture in a simulated skiing accident.

How it works:

An old ski boot has a wooden plug placed snugly inside it acting as a foot. A 3 × 4cm square hole accommodates a 0.5m...

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