Rotational Dynamics Topic

Moment of Inertia

Concept 7 demos

Two wooden meter sticks with large metal masses clamped at different positions, lying on a green surface

Moment of Inertia Meter Sticks

Demonstrates that mass distribution, not total mass, determines rotational inertia. Students rotate sticks with identical mass but different mass placements, directly feeling the dependence of moment of inertia.

Wooden meter stick lying on a table with a clamp holding two disk-shaped masses attached near the 70 cm mark

Balancing the Sword

A meter stick with adjustable clamp masses is balanced vertically on an open palm. With masses high, the large moment of inertia slows angular acceleration, giving time to correct — …

Two-meter wooden ramp on a lab bench, raised at the left end by a scissor jack, with a wooden disk and copper hoop at the top and a foam-lined plastic catch bin at the bottom

Hoop and Disk Race

A hoop and disk of equal mass and radius race down an incline. The disk always wins because its mass is closer to the rotation axis, giving it a smaller …

Rotational Energy

Concept 2 demos

Angular acceleration machine with white pulley wheel on central shaft, two arms with movable brass weights, string with hanging mass, clamped to bench edge with purple Irwin Quick-Grip clamps on wooden blocks

Angular Acceleration Machine

Demonstrates that mass distribution, not just total mass, determines angular acceleration. Students compare the acceleration when the arm weights are close to the shaft versus out at the ends, directly …

Falling chimney apparatus: wooden base board with hinged stick propped up by a vertical support bar forming a triangle, yellow cup and ball bearing visible at the top end of the stick

Falling Chimney - Free-Fall Paradox

A hinged stick ("chimney") rotates faster than a ball bearing free-falls, so the cup at the end of the stick catches the ball. Students see that rotational acceleration can cause …

Conservation of Angular Momentum

Concept 6 demos

Gray metal stool seated inside a wooden rotating turntable, with two gray dumbbells on the stool seat

Rotating Table

Demonstrates conservation of angular momentum. A person on a rotating platform changes speed by moving hand weights inward (faster) or outward (slower), showing the inverse relationship between moment of inertia …

Person standing on a small rotating platform in front of a blackboard, holding a hand weight extended at arm's length

Steering on a Turntable

Demonstrates conservation of angular momentum in a system with zero external torque. Swinging a hand weight on a rotating platform causes the platform to rotate in the opposite direction, showing …

Centrifugal governor at rest on a centrifugal machine, showing two brass balls on hinged arms in the lowered position with a central threaded shaft

Centrifugal Governor

Demonstrates how centripetal force depends on angular velocity. As rotation speed increases, the brass masses swing outward and upward on their hinged arms, illustrating the force balance between tension, gravity, …

Gyros

Concept 6 demos

Two bicycle wheels on a green bench — one with black mag-style spokes and cylindrical axle handle, one with traditional wire spokes and extended axle

Bicycle Wheels

Demonstrates angular momentum conservation, gyroscopic precession, and resistance to axis reorientation. Students observe how angular momentum transfers between a spinning wheel and a person on a rotating platform, making the …

MITAC motorized gyroscope with spinning flywheel (motion-blurred) in a dark metal gimbal frame on a round base, white clip-on mass on the horizontal shaft, red power cord

Mitac Gyroscope

Demonstrates angular momentum as a vector quantity. The motorized gyroscope resists changes to its spin axis, maintaining orientation when the platform beneath it rotates. Clip-on masses create gravitational torque that …

MITAC motorized gyroscope with red rotor disk in green inner gimbal ring and blue outer gimbal ring, mounted on black base with power cord, two wooden blocks with binder clips on table nearby

Motorized Gyroscope

Students observe that a spinning gyroscope maintains its orientation when the base is rotated, demonstrating conservation of angular momentum as a vector quantity. Hanging masses from the frame produce precession …

Rotational Stability

Concept 6 demos

Large colorful pump-action spinning top with concentric rainbow rings, blue conical sections, and a red pump handle, spinning on a small contact point

Standing Top

A pump-action spinning top demonstrates rotational stability: angular momentum allows the top to balance on its point when spinning rapidly but not when stationary. Students observe precession and nutation as …

Two white PVC cylinders on dark fabric, each with different colored marks on their ends — left cylinder has a red X on one end and a blue circle on the other, right cylinder has a blue square on one end and a red rectangle on the other

Rolling and Spinning

Demonstrates that rolling motion is the superposition of translation and rotation. The colored ends of the cylinder make velocity addition visible: the end where translational and rotational velocities cancel appears …

Collection of tops: a large colorful pump-action toy top, a small wooden spinning top, and a red tippe top on a green surface

Tops

The wooden top shows precession and the wobbling motion that develops as a top spins down. The tippe top confounds students: with enough initial angular velocity, it flips over and …