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Collapsible Cow

What it shows:

A small crude spindly model of a cow is able to support five times its own weight. Another model, scaled up exactly six times in all dimensions, collapses under its own weight! Assuming that strength is proportional to cross-sectional area (∝ dimension 2) and weight is proportional to volume (∝ dimension 3), simply scaling the model up geometrically leads to the situation where the weight is too great for its strength.

How it works:

This demonstration was inspired by R.H. Stinson's apparatus note in the AJP (see References...

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Egg Shell Strength

What it shows:

Eggs have a reputation for being quite strong under compressional loads. You won't believe your eyes when you see how strong they actually are — an egg can support a person!

How it works:

An egg shell is a composite material, but primarily calcium carbonate, "nature's ceramic."1 We assume the ultimate compressional strength of the material to be about the same as bone (which is mostly calcium phosphate, but never mind): 170x106 N/m2. The diameter of a "large" chicken egg is about 1.75" and the typical shell...

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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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Coriolis Force

What it shows:

The Coriolis force is a pseudo force existing in a frame that rotates with constant angular velocity to a reference frame. It acts on a body moving in the rotating frame to deflect its motion sideways. Here the audience sits in the reference frame, while two volunteers on a rotating platform experience the coriolis force by trying to basket a volleyball.

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Tennis Racquet Flip

What it shows:

A simple and convincing demonstration of the intermediate axis theorem. Consider an object (a tennis racquet in this case) with three unequal principle moments of inertia. If the racquet is set into rotation about either the axis of greatest moment or least moment and is thereafter subject to no external torques, the resulting motion is stable. However, rotation about the axis of intermediate principle moment of inertia is unstable — the smallest perturbation grows and the rotation axis does not remain close to the initial axis of rotation.

How it works:...

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Coffee Mug on a String

What it shows:

Conservation of angular momentum and the exponential increase in friction are what save the coffee mug from smashing into the floor. Use this entertaining demonstration to introduce either of those physics concepts.

How it works:

You need a pencil, a pen, a china cup (we use a china cup to add suspense and a threat of disaster), and about 1 meter of string. Tie one end of the string to the cup and the other to the pen. Hold the pencil in one hand and drape the string over it so the cup hangs down a few centimeters. Hold the pen with your other hand (arm...

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Three Dumbbells

Lecturer rotates on turntable whilst holding two dumbbells.

What it shows:

Angular momentum, the product of a body's moment of inertia and angular velocity, is always conserved. A reduction in moment of inertia will result in a proportional rise in angular velocity.

How it works:

A volunteer holds the other two dumbbells 1 in each hand and stands upon a rotating platform. 2 With arms outstretched and a little push they begin to rotate at a certain angular velocity. By pulling in their arms to their chest, the moment of inertia is...

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Bungee Jumping Barney

What it shows:

Using conservation of energy, calculate the height from which Barney must jump so that his head just barely kisses the floor at the bottom of his bungee cord jump. Then verify by experiment. Oops ... hate when that happens! It turns out that it's not so simple and there are important details that must be taken into account.

How it works:

Barney (the friendly pink dinosaur) is "sandbagged" (with a 5 kg weight, duct-taped around his waist) and suspended from the sky-hook by a 3.1 meter-long (unstretched) spring. The spring constant has been measured...

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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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Pendulum and Nose

Faith in the conservation of energy is tested by taking the demonstrator's nose to task.

What it shows:

The principle of conservation of energy ensures that a pendulum released at a particular amplitude will not exceed that amplitude on the return swing. A lecturer's faith in their subject is put to the test using a 50lb (22.7kg) iron ball.

How it works:

Technique is very important here. The best method to employ is to stand with your back against the blackboard with your head also touching the board. This ensures that you don't lean forward after release....

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Elastic and Inelastic Collision Model

What it shows:

Two cars have the same mass and same spring bumper. When given a push and allowed to collide with a wall, one car bounces off with only a small reduction in speed ("elastic" collison) whereas the other car comes nearly to a complere stop ("inelastic" collision).

How it works:

There are two impulse cars made of identical materials and have the same mass. The car that models an elastic collision has all its lead sinkers securely attached to the frame so that they can't move. In contrast, the car that models an inelastic collision has the lead sinkers...

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Reaction on Conveyor Track

What it shows:

A straightforward demonstration of Newton's 3rd law, that forces are interactions and thus come in pairs.

How it works:

Two people, each sitting (cross-legged) on their own board, position themselves in the center of the track facing each other. Upon pushing against each other with their hands, they glide apart down the length of the track. Repeat this with one person turned around — the other person pushes on his/her back instead of pushing against each other with their hands. The ensuing motion down the track is exactly the same as before.

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Scantling and Ball

Ball rolling down tilted trough in oscillatory fashion yields acceleration. Also known as Galileo's Inclined Plane).

scantling and ballWhat It Shows

An ingenious experiment to measure acceleration due to gravity first performed by Galileo.

How It Works...

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