Table of Mechanics

Mechanics (1N): Linear Momentum

Mechanics (1R): Properties Of Matter

Lecture Demonstrations

Rotational Dynamics

PIRA classification 1Q

129 Demonstrations listed of which 90 are grayed out

Grayed out demonstrations are not available or within our archive and are under consideration to be added.

1Q10. Moment of Inertia


Demonstration Name




Inertia Wands and Two Students


Give students equal mass wands to twirl, one with the mass at the ends and the other with the mass at the middle.


Inertia Rotator and Two Students

Students rotate a "T" from a disc mounted on the bottom while holding the device by a sleeve. Weights are mounted at different distances on the cross bar.


Torsion Pendulum Inertia

The period of a torsion pendulum is used to determine moment of inertia. Tinker toys allow one to easily construct objects with the same mass but different moments of inertia. Many variations are presented. Objects are added symmetrically about the torsional pendulum axis. Use the torsion pendulum to determine the moment of inertia.


Air Bearing Inertia

Various objects are placed on an air bearing supported rotating disc. The moment of inertia is calculated.


Ring, Disc, and Sphere


A ring, disc, sphere, and weighted discs of the same diameter are rolled down an incline. Each object reaches the bottom at different times due to differing moments of inertia.


All Discs Roll at the Same Speed

A set of weighted discs of different diameters are rolled down an incline at the same speed. Also use hoops and spheres.


Racing Discs

Two discs of identical mass, one weighted in the center and the other weighted at the rim, are rolled down an incline.


Moment of Inertia Spools

Aluminum wheels are joined by two brass cylinders that can be placed at different radii to change the moment of inertia.


Weary Roller

Load a roller with fine dry sand or powdered tungsten. See Sutton M-163.


Spinning Eggs

A raw egg in a torsion pendulum damps more quickly than a boiled egg due to internal friction. It is much easier to begin spinning a hard boiled egg on a plate than it is to spin a raw egg. See Sutton M-60.


Moment of Inertia of a Ball

An air spinner for a 2" bronze ball and a method of mapping out the three axes of moment of inertia.


Errant Pool Balls

Directions for making several different types of weird acting pool balls. See TPT 20(1), 50.


Torsion Pendulum with Swiveling Masses

A torsion pendulum with lead rings for its masses. The rings can be locked into place (a normal torsion pendulum) or allowed to rotate about their local axis. The pendulum is spun


Parallel Axis Theorem

An adjustable double dumbbell on a rotating bar arrangement.


Parallel Axis Wheels

The period of a bicycle wheel suspended as a pendulum is measured with the wheel spinning and locked.

1Q20. Rotational Energy


Demonstration Name




Wheel and Axle I

An old elevator pulley, is the wheel attached to a horizontal axle. A fixed weight on a string is attached to the axle. When the weight is released, the wheel spins.


Wheel and Axle II


Two equal masses are mounted on a radial bar fixed to a horizontal axle with a pulley. A weight is released which causes it to spin. The masses can be moved in and out. The rotational speed and acceleration of the spinning axle can be monitored with a Pasco photogate.


Adjustable Angular Momentum

Spin the air bearing supported rotatable disc with a mass hanging on a string.


Accelerate Light and Heavy Pulleys

Look into of the moment of inertia of a pulley affects a system with pulleys.


Angular Acceleration

Use strobe photography to record the motion of a large disc accelerated by a mass on a string over a pulley.


Dry Ice Pucks I

A dropping mass on a string wrapped around a massive dry ice puck gives both linear and angular acceleration.


Dry Ice Punks II

A dry ice puck with strings wrapped around two different radii going to equal masses hanging on opposite end of the table is stationary while a piece of masking tape is placed over one winding. Remove the tape and the puck spins and translates.


Rolling Spool

A large spool is rolled down an incline on its small axle. When the outer discs reach the table, the thing takes off.


Rolling Spool

Place the rolling spool demonstration on a low friction sheet to show conservation of linear momentum as the sheet moves backward when the roller hits bottom.


Bike Wheel on Incline

A bike wheel rolls down an incline on its axle. The wheel can be pinned to the axle.


Rolling up an Incline

A roller is timed as it rolls up an incline under the constant torque produced by a cord wrapped around over a pulley to a hanging mass.


Start a Wheel

Use a large DC motor and a large wheel to show the angular acceleration of a rotating body with a constant driving torque.


Rolling Pendulum

A spherical bob can roll on a track of the same arc as its swing when suspended by a cord. Comparison of the motion in the two cases shows the effect of the rotational motion in rolling. See AJP 47(4), 367.


Radius of Gyration

Slide an air cart down an inclined instrumented air track, then add a wood track and roll a ball down the same incline. See AJP 46(3), 300.


Spin a Swing

Wind up two balls on strings from a common support with a slack connecting string between them. As they unwind, the angular velocity decreases until the connecting string becomes taut, then increases. See AJP 28(4), 405.


Falling Chimney

A ball at the end of a hinged stick falls into a cup mounted on the stick.


Bowling Ball Falling Chimney

A bowling ball at the end of ten foot ladder jumps into a five gallon pail.


Falling Chimney - Ball Misses

A mass can be added to the end of the bar to slow it down causing the ball to miss the cup.


Falling Chimney - Trajectory

The standard falling chimney demonstration is performed with the caveat that the ball and cup trace out their trajectories on a canvas behind the apparatus.


Pennies on a Meter Stick

Attach a meter stick to a support via a hinge. Support the other one with a stick that goes to the ground. Line the meter stick with pennies and pull out the support. The pennies stay on the part of the stick between the hinge and the center of gravity because it accelerates less than g. The pennies fly off the part of the stick beyond the center of gravity because it accelerates faster than g. It happens very quickly a slow motion video is helpful.


Falling Meter Sticks

Compare the rate of fall of one meter and two meter sticks.

1Q30. Transfer of Angular Momentum


Demonstration Name




Passing the Wheel


The lecturer on a rotating stool passes a spinning bike wheel back and forth to an assistant. Each time it is handed off it is rotated 180 degrees, and the lectures angular momentum increases.


Pass Bags of Rice

Two people stand next to one another on two rotating platforms. One is started rotating and he passes bags of the other one


Drop Bags of Rice

A person on a rotating stool holds out 10 lb bags of rice and drops them. The rate of rotation is not affected.


De-Spin Device

Two heavy weights on cables are released from a vertically spinning disc to slow the system by conservation of angular momentum.


Catch the Bag on the Stool

A person sits on a rotating platform and catches a heavy bag or ball at arms length (off-axis). The person will begin to rotate.


Catch a Ball with an Arm

Shoot a steel ball at a catcher on the end of an arm that rotates. AJP 31(2),91


Drop a Disc on Rotating Disc

A second disc is dropped on an air bearing supported rotating disc. Spark timer recording.


Spinning Funnel

A funnel filled with sand spins faster as the sand runs out. See TPT 22(6),391.


Stick Propeller Device

The stick-propeller device appears to produce angular momentum from nowhere. Obviously it does not, but where does it come from?

1Q40. Conservation of Angular Momentum


Demonstration Name




Rotating Platform and Dumbbells


Instructor stands on a rotating platform and with a set of dumbbell, extend and retract their arms while rotating.


Big Rotating Stool and Dumbbells

A cable pulley system moves large masses from 60 to 180 cm. See AJP 45(7), 636.


Rotating Stool and Long Bar

Sit on a rotating stool holding a long bar with masses at the ends. Rotate the bar one way and you turn the other way.


Rotating Stool and Bat

Stand on a rotating platform and swing a baseball bat.



A flyball governor can be expanded or contracted by squeezing a handle.


Dry Ice Puck Rotators

Two dry ice puck rotators: a) steel balls separate, b) they come together.


Hoberman Sphere


A collapsible sphere suspended from the ceiling is given a spin. A weight attached to the collapse mechanism is dropped causing the sphere to reduce its moment of inertia. Upon collapsing, the rotational speed of the sphere increase showing that angular momentum is conserved.


Watt's Regulator

A model of a Watt's regulator with a valve regulator, also known as a flyball regulator. {Museum Item}


Pulling on the Whirlagig

Balls are attached to either ends of a string that passes through a hollow tube. Set one ball twirling and pull on the other ball to change the radius.


Pulling on the Whirlagig

A ball on a string rolls on the lecture table. In one case the cord wraps itself around a vertical rod. In the other, to cord is pulled through a hole in the table. See Sutton M-186.


Rotating Stool and Bicycle Wheel


A person on a rotating stool, spins a bicycle wheel and turns it over and back.


Stool, Bicycle Wheel, and Friction

Slow down the bike wheel deliberately to emphasize the role of friction in transfer of momentum.


Drop the Cat

A person turns himself around on a rotating stool by variation of moment of inertia. A video of a cat doing this as it falls and a discussion of how they do it.



Go skiing while holding a bike wheel gyro. By conservation of angular momentum, turn yourself with the gyro. Stand on a rotating turntable with skies on to show the upper part of the body turning opposite the lower. See TPT 11(7), 415.


Angular Momentum Train

A circular track on a horizontally mounted rotating platform and a train have the same mass. The train and track move in opposite directions.


Angular Momentum Train - Air Table

The circular track is mounted on a large air table puck. See AJP 41(1), 137.


Frictional Transfer of Angular Momentum

A balanced framework constrains a spinning wheel. As the wheel slows down, the framework begins to rotate. See Sutton M-185.


Coupled Windmills

Two angular momentum machines (see Sutton M-166) are coupled by a spring. The spring is wound and both are released simultaneously to show opposite reactions. See Sutton M-174.


Counter Spinning

An induction motor is mounted so both the frame and armature can rotate freely. No torque is required to tilt the direction of axis of rotation unless either the frame or armature is constrained. See AJP 44(1), 21.


Wheel and Brake

A horizontal rotating bicycle wheel is braked to a large frame and the combined assembly rotates slower. See AJP 57(10), 951.


Pocket Watch

Observe the reaction to the changing angular momentum inside a pocket watch using various techniques. See Sutton M-173.


Orbital Angular Momentum

Apparatus Drawings Project No.33: A dumbbell pivoting on its center of mass, on a counter-weighted rod rotated about its center of mass, remains oriented in the original direction until friction prevails. See AJP 31(1), 42.


Buzz Button

A 6" wooden disc supported by a loop of string passing through two holes drilled 1/2" apart. Directions for showing constancy of axes. See Sutton M-171.


Sewer Pipe Pull

Put "o" rings around a section of large PVC pipe to act as tires. Place on a sheet of paper and pull the paper out from under it.


Paper and Ball

Pull a strip of paper horizontally from under a rubber ball. As soon as the ball is off the strip, it stops dead.


Off-center Flywheel

A flat plate is free to rotate on a block of dry ice. The plate rotates about its center of mass when the flywheel at one end slows down.


Double Flywheel Rotor

Two flywheels free to rotate about a vertical axis on a bar which is also free to rotate about a vertical axis are coupled in various ways to demonstrate "spin-spin" and "spin-orbit" coupling with and without dissipation. See AJP 53(8),735.


Marbles and Funnel

The angular speed of marbles increases as they approach the bottom of a large funnel.


Air Rotor with Deflectors

Run an air sprinkler, then mount deflectors to reverse the jet.


The Feynman Inverse Sprinkler

This 150 year old physics problem is discussed and demonstrated. Much can be found in the way of debate in articles throughout the years. See AJP 57(7), 654,AJP 59(4), 349, and AJP 58(4), 352. This phenomenon is notoriously hard to demonstrate because of the resistance to motion of the fluid in which the sprinkler is submerged. A more modern theoretical explanation can be found in AJP 72(10), 1276.

1Q50. Gyroscopic Motion


Demonstration Name




Precessing Disc

A 6" aluminum disc on a long axial rod is hand spun to show precession due to gravitational torque.


Human Gyroscope

Instructor stands on a rotating platform and with a Spinning bicycle wheel, Rotate the bicycle wheel to transfer it's energy to the rotating platform.


Bicycle Wheel Gyro

Spin a bicycle wheel mounted on a long axle with adjustable counterbalance.


Bicycle Wheel Gyroscope

A spinning bike wheel with two handles is supported by a cable attached to one of the handles.


Suspended Bike Wheel

A ball at one end of a bike wheel axle is placed into a socket on a bearing for demonstrating precession and nutation on a large scale.


Bike Wheel Turnaround

Posts from a rotating platform support both ends of the axle of a bike wheel. One post is hinged so the wheel can be supported from one end only as the platform rotates.


Bike Wheel Precession

Photograph a flashing light attached to the rim of a spinning wheel during forced precession.


Walking the Wheel

A spinning bike wheel is mounted on one end of an axle and the other end has a loop of string held in the hand. Try to get the bike wheel in the vertical position by applying a torque to the string.


Double Bike Wheel Gyro

Two bike wheel are mounted coaxially. Try the standard demos with the wheels rotating in the same direction and in opposite directions. {Museum Item}



A commercially built motorized gyro on a gimbal includes counterweights.


Gigantic Gyro

Make a gyro out of an auto wheel and tire. This is big enough to sit on. See AJP 56(7), 657.


Simple Gyroscope

A tabletop gyroscope with three degrees of freedom shows gyroscopic motion. It can be carried around or put on a turntable.


Suitcase Gyro

A battery powered motor runs a flywheel hidden in a suitcase. Have a student turn around with it.


Magnetic Gyro

There are a number of toys and novelty items that involve gyros and magnets.


Air-Bearing Gyroscope

A large air bearing gyro has a long horizontal shaft with arrow heads for visual emphasis.


Adjustable Precession Gyroscope


A gyroscope has a counterweight with adjustable radial distance causing the rate and direction of precession to change.


Precessing Toy Gyroscope

A pull string gyroscope processes around an axis.


Instantaneous Axis

A bicycle wheel is pivoted at the center of mass and has a disc mounted above the wheel in a parallel plane. The instantaneous axis can be seen as the point of no motion on the upper disc.


Precession of the Equinoxes

A rubber band provides a torque to a gyro framework hanging from a string causing precession.


Precessing Earth Model

A fairly complex gyroscope. See AJP 44(7), 702.


Precessing Ball

A ball placed on a rotating table processes about the vertical axis with a period 7/2 of the table.



A device induces precession and change of weight is noted.



A vertical gimbal-mounted shaft has a gyro on the bottom end and a light bulb and lens on the top. Nutations of the gyro are shown by the moving spot of light on the ceiling.


Motorcycle as a Gyro

A bike wheel on a front fork is hand spun. The handlebars are twisted (but not moved) in the direction opposite to the turn to lay the machine over.



An industrial gyrocompass can be used to discuss practical applications of gyroscopes.


Model Gyrocompass

A model of a gyrocompass for any latitude on the spinning earth.


2 degrees of freedom

A gyroscope in gimbals on a rotating turntable is deprived of one degree of freedom. A slight change of direction will cause a spin flip.


Stable Gyro Monorail car

A monorail two wheel car is stabilized by a spinning gyro.


Ship Stabilizer

A large model ship contains a motorized gyro, which is free to turn on a vertical axis when the ship model is rocked.


Gyro on Stilts

A top-heavy gyro on stilts teeters about its position of unstable equilibrium. See Sutton M-199.


Trapeze Gyros

A gyro on a trapeze is stable only when spinning. Show stability when there are two degrees of freedom.


Ganged Gyros

Ganged gyros are spun in the same or opposite directions.


Gyro Pendulum

A gyroscope is hung from one end of its spin axle by a string and is swung as a pendulum.


Maxwell's gyro

The spindle of a heavy spinning wheel pivoted at its center of gravity will follow an irregularly shaped object. The extended shaft of a gyro supported at its center of mass will trace out complex contours.


Air Bearing Maxwell's Top

An air-bearing Maxwell's top rests on a 2" dia. ball with matching air bearing cup. Tangential air jets provide torque. See AJP 30(7), 503.

1Q60. Rotational Stability


Demonstration Name




Bicycle Wheel Top

Extend the axle of a weighted bike wheel and terminate with a rubber ball.


Humming Top

The standard toy top that you pump up.


Old Fashioned Top

An old fashioned top that you throw with a string.


Yo-yo top

Description of an antique toy demonstrating various aspects of rigid body rotational motion. Several pictures should make it possible to duplicate the thing. See TPT 22(1), 36.


Spinning Coin

An analysis of "wobbling", exhibited by common objects (coins, bottles, plates, etc) when they are spun on horizontal, flat surfaces. The apparatus maintains "wobbling" motion of a metal cylinder, which can be observed in slow motion by means of stroboscopic illumination.|


Tippe Top

The tippe top flips when spun. It spins in the opposite of the expected direction when inverted. Physical arguments are presented which support the convention that the influence of sliding friction is the key to the understanding of the top's behavior. A rigorous analysis of the top's mechanics is offered, together with computer-generated solutions of the equations of motion.


Spinning Football

Spin a football and it raises up on end.


Spinning Eggs

Instead of hard and soft boiled eggs, fill hallow plastic eggs with water, paraffin, or air. If they are spun fast enough they will rise up so that their long axis is vertical. Try to predict which way.


Billiard Ball Ellipsoid

A billiard ball on an air bearing shows the spectacular motion of free rotating rigid and semirigid bodies moving near their inertial singularities. Or, the billiard ball on an air bearing acts goofy when you spin it in certain ways. Or, a billiard ball weighted with brass rods along orthogonal axes will show spin flip. See AJP 44(11), 1080.


Tossing the Book

Throw a book or board up in the air spinning it about its three principle axes, demonstrating the intermediate-axis theorem. Use a simple method of measuring the moments of inertia about the three axes before tossing the book. Also, a simple straw and paperclip inertia wand can help explain. See AJP 46(5), 575, and TPT 17(9),599.


Tossing the Hammer

Note the hammer's rotation about various axes. See TPT 28(8),556.


Spinning Lariat, Hoop, and Disk

A vertically mounted hand drill is attached to a loop of chain, a hoop or a disk by a wire. See the University of Minnesota website.


Spinning Bar

A bar is hung from one end by a string on a hand drill. When spun, the bar will rise. Also spin a loop of chain.


Spinning Box

A rectangular box rotated from a chain around any of the three principle axes will rotate about the axis of maximum rotational inertia.


Rotating Vertical Chain

The five stable patterns observed in a vertical rotating chain are used to introduce Bessel's function. See AJP 48(1), 54.


Spinning Bifilar Pendula

A variable speed motor drives a horizontal rod in a horizontal plane with bifilar pendula of different lengths attached.


Orbital Stability

Identical masses slide out on a horizontally rotating cross-arm both attached to the same central hanging mass. See AJP 30(8), 561.


Quadric Restoring Force

A leaf spring provides a quadratic restoring force to dumbbells rotating on a crossarm. Each angular velocity corresponds to only one stable orbit.


Rotational Instability

Different springs will result in conservation of angular momentum or instability in a spring loaded dumbbell.


Linear Restoring Force

Two dumbbells slide out as a crossarm rotates with a spring providing the restoring force. At the critical angular velocity the orbits are stable at any radius.


Static and Dynamic Balance

A rotating system suspended by springs shows both the difference between static and dynamic balance.


Dynamic Tire Balancing

Analysis of dynamically balanced wheels shows they must also be statically balanced.


Marion's Dumbbell

A simple apparatus to demonstrate the non-colinearity of the angular velocity vector and the angular momentum vector. Helps students increase their understanding of angular velocity, angular momentum, and the inertial tensor. Theory and construction details.



fw: RotationalDynamics (last edited 2018-07-18 17:20:53 by srnarf)