The Michelson-Morley Experiment

This applet presents a historical recreation of the Michelson-Morley experiment in which the existence of the ether was disproved.

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Muon Decay

Users can recreate the famous Rossi-Hall experiment from 1940. They will compare the muon flux at different points of the atmosphere as the unstable subatomic particles travel to earth.

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Photon Clock

This applet helps to visualize what time dilation is and why it happens. By measuring time with the very precise and accurate photon clock, users can see first hand the effects of moving a clock has on time.

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Spacetime Diagrams

This applet follows a rocket as it travels at speeds near the speed of light. Using a printable graph, users can draw the path the rocket takes, then compare how time has passed for members inside and outside of the rocket. Run Applet

Spacetime diagrams in more than one reference frame is a useful drawing tool. Users can draw and compare events in two different reference frames on a printable graph and observe why the Lorentz contraction, time dilation and other effects occur. Run Applet


This expository applet works through two examples of simultaneous events occurring in different reference frames. Users will see worked examples using the above spacetime diagrams in order to understand that the velocity of a reference frame affects simultaneity.

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Another useful drawing tool, the four-momentum applet helps users to see how four-momentum is conserved in moving reference frames by drawing four-vectors on a printable graph.

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Mass-Energy Equivalence

This applet can be used to illustrate Einstein's September 1905 paper in which mass-energy equivalence is established. Links to original source literature as well as an adapted version of Einstein's paper are also included.

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Synchronized Clocks

This applet explains what is meant by the term "synchronized" in special relativity and demonstrates how time dilation implies length contraction.

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Length Contraction and Appearance of Relativistic Objects

For decades after the original 1905 paper in which length contraction was discussed physicists had a completely wrong notion of what fast moving objects would look like. This applet explores the difference between shape and perceived shape for relativistic objects.

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Doppler Effect and Appearance of a Relativistic Clock

This applet explores the relativistic Doppler effect and what a moving clock would "look like" to an observer.

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