Table of Mechanics

Mechanics (1H): Newton's Third Law

Mechanics (1K): Applications of Newton's Laws

Lecture Demonstrations

Statics of Rigid Bodies

PIRA classification 1J

83 Demonstrations listed of which 46 are grayed out.

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

1J10. Finding Center of Gravity


Demonstration Name




Center of Gravity

Toss into the air many different shapes all of which have their center of mass marked with a bullseye.


Wooden State Map


Suspend a map of the state from holes drilled at points to find the "center of the state".


Hanging Irregular-Shaped Board


Suspend an irregular-shaped board from several points, and use a plumb bob to find the center of gravity.


Hanging Potato

Hang a potato from several positions and stick a pin in at the bottom in each case. All pins point to the center of gravity.


Meter Stick on Fingers

Slide your fingers together under a meter stick and they meet at the center of gravity. Add a baseball hat to one end and repeat.


Center of Gravity of a Broom

Find the center of gravity of a broom, hang a 1 kg mass somewhere on the broom, find the new center of gravity, calculate the weight of the broom by equating torques.


Loaded Beam - Moving Scales

Slide the scales together under a loaded beam noting the scale readings of the moving and stationary scales.


Your Center of Gravity

Two methods for measuring the center of gravity of a person are shown. Your Center of Gravity

1J11. Exceeding Center of Gravity


Demonstration Name




Leaning Tower of Pisa

A model of the tower constructed in sections. Adding the top will cause it to tip over.


Falling Cylinders

A tube, weighted at the bottom, falls when a cap is added. An upright cylinder, containing two balls, falls when a weighted cap is removed. AJP 34(9), 822


Tipping Block on Incline

A block is placed on an incline and the incline is raised until the block tips.


Leaning Tower of Lire


Stack blocks stair-step fashion until the top block sticks out beyond any part of the bottom block.


Leaning Tower of Lire


Use 6"x6"x2' wood blocks and have a student sit under the stack as it is built.


Cantilevered Books

The number of books necessary to overhang 2,3,4, etc lengths. See AJP 41(5),715.


Instability in Flotation

A device to raise the center of mass in a boat until it becomes higher than the center of bouncy, and the boat flips. See Sutton M-287.


Center of Mass and Balance in People

Pictures of three center of mass objects and several person based center of mass tasks e.g., stand on your toes facing the wall, etc. Center of mass revisited


Double Cone on Rails

As a double cone moves up a set of inclined rails, its center of gravity is lowered to the height of the rails.

1J20. Stable, Unstable, and Neutral Equilibrium


Demonstration Name




Bowling Ball Stability


A bowling ball is placed in, on, and along side a large plexiglass hemisphere to show the types of equilibrium.


Stability of Shapes


A cone balancing on its point is unstable, a block is stable, a sphere is neutral.


Wood Block Stability

A block and support have marks that show whether the center of gravity has moved up or down when the block is displaced.


Block on the Cylinder

A rectangular block of wood is placed on a cylinder first with the width less than the radius (stable) and then with the width greater (unstable).


Catenary Surface

A large block is always in stable equilibrium anywhere along this catenary surface. See Sutton M-40.


Fork, Spoon, and Match

Place a spoon and match in the tines of a fork and balance the assembly on the edge of a glass.


Two Forks and a Toothpick

Two forks and a toothpick can be balanced on the edge of a glass while the water is poured out.


Nine Nails on One

A technique to balance ten landscape spikes on the head of a single upright spike.


Sky Hook

A complete solution to the hanging belt problem. TPT 14(8), 499


Spoon on Nose

Hang a spoon on your nose. Most effective with giant food service spoons.


Horse and Rider

Stable equilibrium of the horse and rider. Note that the COG is below the contact point.


Balancing Man

Stable equilibrium of the balancing man. Note that the COG is below the contact point.


Clown on Unicycle

A toy clown rides a unicycle on a wire.


Tightrope Walking Model

A model of a tightrope walker shows the center of mass moves up with tipping.


Balancing a Stool

Construct a stool so that wires crossed diagonally will intersect at the center of gravity. The stool can be oriented in any direction.


Chair on Pedestal

Attach heavy weights in the ends of a chair's legs so it will balance on a vertical rod placed under the seat.


Broom Stand

Spread the bristles and a straw broom will stand upright.


Wine Bottle

Stick the neck of a wine bottle through a hole in a slanted board and the whole thing stands up.


Glass on Coin

A glass container 2/3 filled with water will balance on its edge on a coin. See TPT 14(1), 39.

1J30. Resolution of Forces


Demonstration Name




Simple Block on a String

This is a concept demo. Describe/Depict all Forces that are acting on the block when stationary, being pushed by a finger, or pulled by it's string.


Suspended Block


Forces are placed upon a block on an inclined plane such that the block maintains its position after the plane is removed.


Normal Force

A block on an incline has an arrow mounted from the center of mass perpendicular to the surface with "N" on the arrowhead and another arrow hanging from the center of mass with a "g" on the arrowhead.


Hanging the Plank

A heavy plank is suspended from three spring scales in several configurations: series, parallel, and a combination. See Sutton M-9.


Climbing Rope

A heavy climbing rope is hung from the ceiling, and someone can climb or hang from it.


Tension in a String

The weight of a mass hung from a single spring scale is compared to the weight shown on a spring scale between two masses over pulleys.



Two people pull in opposite directions on opposite ends of a rope demonstrating vector addition of the two input forces.


Tension in a Spring

Two students pull against each other through one and then two spring scales.


Tension in Springs

Masses are hung at the ends of a series of spring scales.


Rope and Three Students


Two large, strong students pull in opposite directions on the ends of a rope. A small student then pushes/pulls on the middle of the rope in a direction perpendicular to the rope.



Hang a 5 N weight from a line and pull on one end of the line with a spring scale.


Rope and Three Weights

Suspend a rope over two pulleys with masses on the ends and hang another mass from the center. Measure the deflection. An alternative set up would be a rope mounted to a frame with a spring scale measuring the tension.


Break Wire with Hinge

Suspend a 5 kg mass from a length of wire. Break a length of similar wire by placing the same mass on the back of a large hinge. And opening it by pushing down. See Sutton M-16.


Pull the Pendulum

A long heavy pendulum is displaced with a horizontal force, measured by a spring scale.


Horizontal Boom

A 1 m rod is suspended from a vertical rod at two points: an open bracket holds one end of the 1 m rod tight to the vertical rod, allowing it to swivel, while a string tied to the vertical rod is attached to the opposite end of the 1 m rod. A weight is then hung off the far end of the now horizontal 1 m rod. The tension in the wire can be measured with a spring scale.


Blackboard Force Table

A blackboard with grid lines on which to draw forces in chalk.


Vertical Force Board

A vertical whiteboard to draw the force vectors of a balance's object through a continuous range of angles.


Force Table on Overhead

A plexiglass force table for the overhead projector. See AJP 41(9), 1115


Force Table with Torque Apparatus

The standard force table, three dimensional force table, and torque apparatus.


Force Table

Three scales and a ring to show forces add by parallel construction. Not the usual. See 1J30.52.


Bosun Chair Force Table

Sit on a chair suspended from two supports equipped with protractors and commercial load cells. See AJP 51(6), 571


Blackboard Force Table - Rubber Band

Determine the spring constant of rubber bands, then predict the mass of an object hung in a nonlinear configuration. See TPT 13(4), 246


Sail Against the Wind

Use a large fan to blow at an air track car or a boat with a sail. Sailboats can sail into the wind, though not directly. Most boats have a forbidden sector of 90 degrees, 45 degrees on either side of the wind direction. See AJP 40(8), 1172


Sail a Trike Against the Wind

A wind driven tricycle moves against the wind. A windmill on the boat drives a wheel. See AJP 49(3), 282


Sail Against the Wind

A wind driven boat accelerates against the wind. A windmill on the boat drives a propeller underneath. See AJP 46(10), 1004


Floating Ladder Problem

A stick is hung by a thread at one end with the other attached to a large float on water. The 'ladder' can be put at any angle but since the float is floating it will move in such a way to reach equilibrium. See Sutton M-29.


Sand in a Tube

Place a tissue on the bottom of an open glass tube, fill with a few inches of sand and push down on the top of the sand with a rod. A couple of inches of sand held in a tube by tissue paper will support about 50 lbs. See Sutton M-7.


Stand on an Egg

Three eggs in a triangle pattern in foam depressions between two plates will support a person. A raw egg can be squeezed between two hard foram rubber pads with a force of over 150lbs.


Rolling Wedge

Three cylindrical rollers are mounted together to form a wedge. At the bottom of the inclined plane is a hinge that connects it to a plank that goes all the way back up to the top and sits on top of the roller car. A weight is placed on top of the plank. As the wedge rolls down the plane it lifts the weight. See Sutton M-19.


Inverse Catenary

A string of helium balloons tied at each end forms an inverse catenary. See AJP 59(5), 472

1J40. Static Torque


Demonstration Name




Torque Bar


Use wrist strength to lift a weight suspended from a sliding collar at various distances from the handle.


Torque wrench

Modify a torque wrench so weights can be hung at different distances. It can be used to break aluminum and steel bolts. See TPT 15(2), 115.


Wrenches of Different Length

Show wrenches of different lengths and explain on more length means more torque, necessary for larger bolts.


Meter Stick Torque Beam


A meter stick, suspended at the center, is used as a torque balance. Different combinations of weights hung at different distances can keep the beam balanced demonstrating how torque works.


Hinge Board

Use a spring scale to lift a hinged board from various points along the board.


Walking the Plank

Place a 50 lb block on one end of a long 2x6 in plank and hang the other end off the lecture bench. Walk out as far as you can. This can also be done on a smaller scale with two masses and a smaller plank.


Torque Board

A whiteboard tear drop shaped wheel is mounted vertically on its CM horizontal axis so that it can spin freely. Various weights can be hung on it at various points. The wheel will then rotate to its new equilibrium.


Torque Wheel

A circular wheel is mounted vertically on a horizontal axis so that it can spin freely. Various weights can be hung on it at various locations. It will spin to equilibrium. See Sutton M-28.


Torsion Shaft

The apparatus shows the proportionality between torsional deflection and applied torque. Twist a shaft by applying torque to a disc affixed to the top. The shaft should be colored in such a way to show the torsional deflection.


Opening a Door

Walk over to the classroom door and open it by pulling or pushing on various distances from the hinges.


Truck on a Bridge

A model bridge is hung from several spring scales and a heavy model truck drives across. See Sutton M-23.


Loaded Beam

Support the loaded beam with spring scales or platform balances. See Sutton M-26.


Galileo Lever

An apparatus shows the conditions for static equilibrium. Two sections of ruler of different lengths are connected to a larger ruler of length equal to the sum of the smaller two. The smaller two are bolted to the large piece so that they may be rotated. The small piece is bolted at its center of gravity. The larger one is not so rotating it results in a net torque. See Sutton M-21 and M-22, or Purdue's Demo Website.


Roberval Balance

An unequal arms balance. The position of weights does not affect the equilibrium. See TPT 22(2), 121.


Roberval Pan Balance

A large model of the Roberval platform balance. Neutral equilibrium is maintained at any position on the platform. It is a pan balance that utilizes the concept of an unequal arms balance so that the position of mass in the pan does not affect the equilibrium. See the Wikipedia article.


Platform Balance

Explain the operation of a platform balance. See Sutton M-41 and M-42.


Steelyard Balance

Explain the operation of a steelyard or weighbridge balance. See Sutton M-41.


Suspended Ladder

Model of a ladder suspended from two pairs of cords inside an aluminum frame.


Hanging Gate

A gate initially hangs on hinges, then add cords and remove the hinges leaving the gate suspended in mid air.


Arm Model

Place a spring scale on a skeleton in the place of the biceps muscle and hang a weight from the hand. See The University of Minnesota Website.


Arm Model

Use an arm model simulating both biceps and triceps muscles to throw a ball.

Table of Mechanics

Mechanics (1H): Newton's Third Law

Mechanics (1K): Applications of Newton's Laws

Lecture Demonstrations



fw: RigidBodies (last edited 2020-11-12 16:07:36 by srnarf)