Heller Model Kits

The Point Charge Forces in One-Dimension model investigates the electric force that one charged particle exerts on another. It is a very simple representation that promotes understanding of Coulomb's Law in three ways: First, students can set the amount of charge on each particle and view vector...

The Ejs Lagrange Top model displays the motion of a heavy symmetric top under the effect of gravity. The top has an initial angular speed that provides the precessional, nutational, and rotational speeds. The ratio of Lz to Lx can be set via slider and the initial angular position and angular...

The Simultaneity Spacetime Diagram model uses light-trajectories to show the effect of relative motion when observing (recording) events in special relativity. In the default scenario, an explosion (an event) at the center of a right-moving stick occurs at t=0 and the arrival of the explosion...


Platforms: Mac

The EJS Molecular Dynamics model is constructed using the Lennard-Jones potential truncated at a distance of 3 molecular diameters. The motion of the molecules is governed by Newton's laws, approximated using the Verlet algorithm with the indicated time step. For sufficiently small time steps dt,...


Platforms: Mac

The Ejs Foucault Pendulum model displays the dynamics of a Foucault pendulum. The simulation is designed to show the dynamical explanation of why precession of the Foucault pendulum is slower at lower latitudes. The simulation shows simultaneously the motion with respect to the inertial...


Platforms: Mac

The Equatorial Coordinates model displays the position of a star in equatorial (Right Ascension/Declination --- RA/Dec) coordinates. The horizon is shown along with the four cardinal directions (N, E, S, and W). The Latitude slider changes the latitude of the observer which is shown by the change...


Platforms: Mac

The Ejs Inertial Oscillation model displays the motion of a particle moving over the surface of an oblate spheroid. The spheroid is flattened to an ellipsoid of revolution because it is rotating, just as the Earth is flattened because it is rotating. The particle is confined to motion along the...


Platforms: Mac

The EJS Equinox Precession model illustrates the Copernican theory of Earth's orbit around the sun. The top window shows a view from outside the celestial sphere. The simulation shows the moving Earth along with its axis or rotation and the line of sight from Earth, through Sun, to the Celestial...


Platforms: Mac

The Ejs Coin Rolling without Sliding on an Accelerated Platform model displays the dynamics of a coin rolling without slipping on an accelerated platform. The simulation displays the motion of the coin as well as the velocity vectors for the surface of the coin and the platform. The initial...


Platforms: Mac

The Ejs Damped Driven Harmonic Oscillator Phasor model displays the motion of damped driven harmonic oscillator. The resulting differential equation can be extended into the complex plane, and the resulting complex solution is displayed with the real part of this solution being the position of...


Platforms: Mac

The Ejs Quartic Oscillator model displays the motion of a bead moving without friction along a horizontal rod, while tied to two symmetric springs. Both the motion of the masses and the phase space plot are shown in the simulation. The natural length of the springs can be changed via textboxes....


Platforms: Mac

The Ejs Normal Modes on a Loaded String model displays the motion of a light string under tension between two fixed points. The string is also loaded with N masses located at regular intervals. The number of masses on the string can be changed via textboxes. You can modify this simulation if you...


Platforms: Mac

The Ejs Strange Harmonic Oscillator model displays the motion of two masses connected by a massless rigid rod and the masses may move without friction along two perpendicular rails in a horizontal table. The energy of the oscillator system can be changed via a slider. You can modify this...


Platforms: Mac

The Driven Mass and Spring Mesh model displays the dynamics of a 2D array of masses coupled by springs and driven by a sinusoidal force. The model shows a time-dependent animation of the displacement or each mass. The driving force can be applied at a single point (shown in red) or uniformly at...


Platforms: Mac

The Diffraction and Interference Model: Single and Double Slits shows diffraction and interference patterns from a single slit, double sources and double slits. The user can change the source wavelength, slit width, separation and distance between slit and screen. The Diffraction and...


Platforms: Mac

The Eratosthenes model displays the shadows cast by two gnomons (sticks) at different locations on Earth. For one gnomon, Sun is directly overhead (as would be the case if the gnomon was on the Tropic of Cancer at the summer solstice). The other gnomon is due north of the first gnomon. The sizes...


Platforms: Mac

The Ejs Waves and Phasors model displays the motion of a transverse wave on a string and the resulting phasors for the wave amplitude. The simulation allows an arbitrarily polarized wave to be created. The amplitude, period, phase velocity and number of phasors displayed can all be changed via...


Platforms: Mac

The Ejs Transverse Wave model displays the motion of a transverse wave on a string. The simulation allows an arbitrarily polarized wave to be created. The magnitude of the components of the wave and the relative phase between the components of the wave can all be changed via sliders. You can...


Platforms: Mac

The Ejs Resonance in a Driven String model displays the displacement of taut string with its right end fixed while the left end is driven sinusoidally. The driving frequency, amplitude, and the simulation's dt can be changed via text boxes and the motion can be further fine tuned by zooming in...


Platforms: Mac

The EJS Angular Acceleration of a Contracting System model shows a mass and pulley system to illustrate what happens when a rotating system contracts. When the centripetal force has contracted a rotating system to half its initial radius then: (1) The tangential velocity has doubled, (2) The...


Platforms: Mac