Lecture Demos: Mechanics

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Shive Wave Model

Thin rods are mounted on a fine wire that twists easily.

PIRA Code(s): 
3B10.30
Set up time: 
none
Physics and Science Concepts: 
Torsion Waves, Waves and Oscillations
Operation: 
Displace the rod at one end to create a torsion pulse or wave. The other end can be left free to move, fixed in place, or critically damped. To damp the model, clip the damping cup to the last rod on one end to get an inverse reflex wave. The damping clip on the rod ends the wave entirely.
Safety: 
None

Centrifugal Force Paradox

In one demo, a wooden frame with two curved tubes is situated on a turntable. As the frame is spun, centrifugal force causes the ball in each tube to move outwards and up the curve of the tube. The other demo shows the same concept. As the frame is spun , the green liquid in it moves towards the outer edges of the frame, also due to centrifugal force.

PIRA Code(s): 
1Q30.60
Set up time: 
10 minutes
Physics and Science Concepts: 
Centrifugal force
Operation: 
Spin the frame and watch the two balls move outwards. For the plexiglass demo, squirt green liquid (or pour) into the frame so that the liquid is at least an inch deep. Then, plug in the cord.
Safety: 
Make sure objects and people are well clear of the spinning frame. Wear safety goggles during operation.

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.

Rotating Stool and Spinning Bicycle Wheel / Suspended Bicycle Wheel

 Rotating Stool and Spinning Bicycle Wheel / Suspended Bicycle Wheel

When holding a spinning bicycle wheel and standing on a platform with the ability to rotate, you can cause yourself to spin by changing the wheel’s axis of rotation.

 

While holding a string attached to the axle of the bicycle wheel, the spinning wheel will remain perpendicular to the floor.

PIRA Code(s): 
1Q40.30
PIRA Code(s): 
1Q50.24
Set up time: 
3 minutes
Physics and Science Concepts: 
Mechanics, Rotational Dynamics
Operation: 
Stand on the stool as it remains still. Have someone start the motor and place the bicycle wheel next to it to get it to start spinning. Take the spinning wheel in your hands and turn the wheel in a horizontal position and you should spin. When the wheel is placed vertical again, you will spin the opposite direction. Use the motor to start the wheel spinning. Hold on to the cord attached to the axle and the wheel will remain vertical.
Safety: 
Do not get items caught in the motor or the spokes of the tire. Hold wheel out from the body as far as possible

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