Lecture Demos

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Variable Angle Pendulum

 Variable Angle Pendulum

A physical pendulum is mounted on a bearing so the angle of the plane of oscillation can be changed. As you increase the angle, the frequency at which the pendulum swings will decrease.

PIRA Code(s): 
3A10.40
Set up time: 
none
Physics and Science Concepts: 
Oscillations
Operation: 
Push the pendulum so that it swings back and forth at an angle of about 0 º. Then, slowly increase the angle, and watch the frequency decrease. For a more effective demonstration, start the pendulum at a relatively high angle, and then decrease the angle of the plane of oscillation so that the frequency of the pendulum will increase over time.
Safety: 
None

Upside-Down Pendulum

Upside-Down Pendulum

A weight is attached to a hacksaw blade so that it can move up and down the blade to change the frequency.

PIRA Code(s): 
3A10.20
Set up time: 
1 minute
Physics and Science Concepts: 
Oscillations
Operation: 
Move the weight along the hacksaw blade. Pull back on the blade and release. When the weight is at the top of the blade the frequency is smaller compared to when the weight is at the bottom.
Safety: 
Edge of blade may be sharp.

Magdeburg Sphere

Magdeburg Sphere

The Magdeburg Sphere is a ball split in half with handles on either piece. When the two halves are placed together and the vacuum pump is used to evacuate the air inside, it becomes extremely difficult to separate the pieces due to external air pressure.

PIRA Code(s): 
2B30.30
Set up time: 
3 minutes
Physics and Science Concepts: 
Fluid Mechanics, Statics of Fluids
Operation: 
Place the two halves together. Put the vacuum pump on the valve and evacuate the air inside. Try to separate the pieces. Vacuum pump not included; it must be obtained from demo 3B30.30.
Safety: 
None

Crystal Structures

Crystal Structures

These are models of different crystal structures.

PIRA Code(s): 
1R50.20
Set up time: 
none
Physics and Science Concepts: 
Properties of Matter
Operation: 
Show the class the structures.
Safety: 
None

Moduledra Crystal Models

Moduledra Crystal Models

Polyhedral building blocks are used to demonstrate crystal structures

PIRA Code(s): 
1R50.17
Set up time: 
1 minute
Physics and Science Concepts: 
Properties of Matter, Minerals
Operation: 
Show the class the blocks to demonstrate atomic crystal structures.
Safety: 
None

Gyroscope on turntable

Gyroscope on turntable

A gyroscope in a gimbal sits on a rotating table made out of two wooden blocks. Rotating the whole gyroscope assembly in the opposite direction of the spinning gyroscope causes the gyro to flip.
 

PIRA Code(s): 
1Q50.60
Set up time: 
2 minutes
Physics and Science Concepts: 
Rotational dynamics, Mechanics
Operation: 
Use the string or turn the rotor with your thumb to start the gyroscope spinning. Take care to hold the gyroscope and metal hold in place relative to the top block of wood. Then, spin the wooden block, stop it, and reverse the direction of the spin. The gyroscope will do a spin flip.
Safety: 
None

MITAC gyroscope

MITAC gyroscope

A commercially built motorized gyroscope on gimbals spins when plugged in.

PIRA Code(s): 
1Q50.30
Set up time: 
1 minute
Physics and Science Concepts: 
Rotational Dynamics, Mechanics, Gyroscopic Motion
Operation: 
Rotational Dynamics, Mechanics, Gyroscopic Motion
Safety: 
The central gyroscope is quite heavy and can pinch fingers.

Hero’s Engine

Hero’s Engine

A flame torch is used to boil water inside a flask that hangs by a string. Jets of steam flow from perpendicular nozzles and rotate the flask. The flask is partially filled with water and heated until steam is produced. The steam emerges from right-angle arms on the side of the flask, causing it to rotate in the direction opposite to that of the
emerging steam

PIRA Code(s): 
1Q40.80
Set up time: 
5 minutes
Physics and Science Concepts: 
Rotational Dynamics, Conservation of Angular Momentum,
Operation: 
Partially fill flask with water. Attach flask by string to ring stand. Then, use a Bunsen burner or a torch to heat the flask. The flask should rotate as the steam emerges from the arm.
Safety: 
Use caution around Bunsen burner or torch. Do not overheat the glass as it may shatter. Eye protection should be worn. The torch can be acquired from the machine shop if necessary.

Moment of Inertia

Moment of Inertia

The moment of inertia of a roto-dyne wheel increases as the radial masses are added and moved outward radially. Assuming that the radial masses are point masses added at a distance (r) from the center of rotation, the increase in moment of inertia is expected to be:

I = I 0 + Mr 2

where M is the total mass added (4X 225g) and r is the radial distance at which it is added and Io is original moment of inertia.

PIRA Code(s): 
1Q40.42
Set up time: 
1 minute
Physics and Science Concepts: 
Moment of Inertia, Mechanics
Operation: 
Instructions included in box. Must obtain ring stand and clamp from 9C40.71 and 9C40.72, respectively. A known weight attached to a string around the wheel torques the wheel a constant amount.
Safety: 
Use caution around spinning wheel.

Angular Momentum Train

Angular Momentum Train

An electric model train runs on a circular track which is supported so that it is free to turn about its center. The moment of inertia of the train is comparable to that of the track and supports. Thus, if the train is started in the forward direction, the track begins to move in the opposite direction, and if the train is brought to a halt, the whole system stops.

PIRA Code(s): 
1Q40.40
Set up time: 
5 minutes
Physics and Science Concepts: 
Mechanics, Angular Momentum, Rotational Dynamics, Angular Momentum, Relative Motion
Operation: 
Place the train on the track. Plug the track into the variac and start the train by moving the dial.
Safety: 
Watch for sparks from the train. Maintain a cautious distance from the wheel.