Lecture Demos: Mechanics

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Rotary Motion

Rotary Motion

Centrifugal hoops and governor, when rotated, will show oblation. The balls on the governor will move outwards and compress the spring as the governor is rotated. The centrifugal force that supposedly causes this is actually due to inertia, and explains why the earth and other planets have a slight bulge around the part that rotates fastest. The rotational motor can also be used with a glass sphere partially filled with a colored liquid. When the sphere is spun, the liquid will rise along the inside edge of the sphere due to centrifugal force.

PIRA Code(s): 
1Q40.23
Set up time: 
1 minute
Physics and Science Concepts: 
Rotational Dynamics, Centrifugal Force, Oblation
Operation: 
Place the shaft of the device into the hole and tighten the screw. Then, plug in the motor and turn on the red switch. When spun, the hoops will show oblation, the balls on the governor will move outwards, and the liquid in the glass sphere will move to the edge of the sphere.
Safety: 
Wear goggles when running the apparatus and keep hands away from the belt.

Trebuchet

Trebuchet

A model trebuchet is used to hurl projectiles using counterweights.

PIRA Code(s): 
1Q20.99
Set up time: 
3 minutes
Physics and Science Concepts: 
Mechanics, Rotational Energy
Operation: 
Take the arm and put it in the slots on the trebuchet. Put the projectile into the green pouch and place the string around the end of the rod. Stick the pin through the three eyelets on he arm and base of the apparatus. Then load the counterweight onto the end of the arm near the wheels. Pull the string to launch the trebuchet.
Safety: 
Do not attempt to catch the projectile. Stay out of the projectile’s path. Stand clear of the swinging arm. The trebuchet is capable of flinging projectiles 20 meters or more, so choose projectiles and counterweights wisely. Safety glasses must be worn when operating.

Newton’s Cradle

Newton’s Cradle

Five balls of equal masses are suspended by strings and aligned in a row. The balls can be pulled back and made to collide to show the conservation of linear momentum.

PIRA Code(s): 
1N30.10
Set up time: 
1 minute
Physics and Science Concepts: 
Conservation of linear momentum
Operation: 
Pull back a number of balls and let them collide with the other balls, allowing the same number of balls to be released on the other side.
Safety: 
Align the balls for the best results. Do not allow the strings to tangle.

Loop the loop

Loop the loop

A ball rolls down an inclined plane and around the loop.

PIRA Code(s): 
1M40.20
Set up time: 
none
Physics and Science Concepts: 
Mechanics, Work and Energy, Conservation of Energy, Centripetal Force
Operation: 
Place ball at the top of track and let it fall. To show students the minimum height required to loop the loop, place the ball on the track at a height that is about double the height of the loop.
Safety: 
Do not stand where the ball exits the track.

Nose Basher

Nose Basher

A bowling ball is suspended from the ceiling by a chain. If a stationary person holds the ball against his nose, and releases the ball without giving it an initial velocity, the ball should not strike the person on its return swing.

PIRA Code(s): 
1M40.10
Set up time: 
5 minutes
Physics and Science Concepts: 
Mechanics, Work and Energy
Operation: 
Hook the bowling ball onto the chain. Pull the bowling ball back until it reaches your nose. Release the ball and do not move. Let the ball come back and show how it will not reach your nose again. *For use in lecture room 131.
Safety: 
Do not give the ball an initial velocity or move forward once the ball is release. Warning: it’s hard not to flinch.

Equilibrium of Forces – Inclined Plane

Equilibrium of Forces – Inclined Plane

Given an angle of inclination a of the inclined plane, this apparatus demonstrates that the mass m required to hold a low friction box of mass M at equilibrium on the inclined plane is given by:

mg = Mg sin a

PIRA Code(s): 
1M20.30
Set up time: 
5 minutes
Physics and Science Concepts: 
Equilibrium of forces, Mechanics, Work and Energy
Operation: 
Set the empty friction box on the incline with weights attached to the string on the other side of the pulley so that the box slides forward. Then, gradually increase the angle of the plane until the box and the weights reach equilibrium.
Safety: 
None

Pulleys

Pulleys

This is an assortment of different size pulleys.

PIRA Code(s): 
1M20.10
Set up time: 
none
Physics and Science Concepts: 
Mechanics, Mechanical Advantage, Simple Machines
Operation: 
These may be used by themselves or with other demonstrations.
Safety: 
None

Conic Sections

Conic Sections

A wooden cone is cut to demonstrate the basic conic sections: the circle, ellipse, hyperbola, and parabola.

PIRA Code(s): 
1L20.40
Set up time: 
5 minutes
Physics and Science Concepts: 
Gravity
Operation: 
Remove pieces from the cone to show different conic sections.
Safety: 
Nails that connect pieces may be sharp.

Inclined Plane with Friction Box and Weights

Inclined Plane with Friction Box and Weights

A friction box can be filled with various weights and placed on an inclined plane. The angle that the box begins to slide should not change as weights are added because the coefficient of friction does not depend on the mass of the object.

PIRA Code(s): 
1K20.35
Set up time: 
2 minutes
Physics and Science Concepts: 
Friction, Angle of Repose, Mechanics, Coefficient of Friction
Operation: 
Set the empty box on the incline and increase the angle until sliding ensues. Add weights to the box and repeat the experiment. The weighted box begins to slide at the same angle.
Safety: 
None

Double Cone

Double Cone

When the double cone is placed on the narrow end of the V-shaped rails it rolls to the wide end. The double cone appears to be rolling uphill, but in reality the center of mass is moving down. *

*Description taken from University of Maryland.

PIRA Code(s): 
1J11.50
Set up time: 
1 minute
Physics and Science Concepts: 
Center of mass, Conservation of Energy
Operation: 
Set cylinder at top of V. Set cone at bottom of V.
Safety: 
None

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