This page contains links to demonstrations that illustrate concepts covered in 131-132-133. Make sure to see the list of sites at the end where you can find more virtual demos.

Most of these demonstrations require that Java be enabled on your browser.

 Bright Yellow indicates the demos appropriate for this week.



Coulomb's law

This should be pretty easy. Test yourself to be sure.
Unknown charge

This is harder. Try it.
Force on charges

Determine the sign of the unknown charges. Hint: move some of the charges away from the others to simplify the problem. You are working with a square-law force.
Charge in a field

See the motion of a particle in a combined electric and magnetric field. You control all the conditions.
(Turn the magnetic field off, at least at first. A good combination to start with is: y=50, Vx=15, Ez=10 and all other quantities zero. You should be able to predict the shape of the trajectory before you try it.)
E-field plotter 1

Plots field lines and equipotentials for an arbitrary charge distribution of your choice. You can also let your system evolve with time. Start with only "electric field lines" selected. Then add equipotentials when you're ready.
E-field plotter 2

Hit the "Start SimPhysics" button to get going. This one has many, many extra features, but I like the one above better. One nice addition is a cursor that shows the E-field direction and magnitude at any point. You might want to start by selecting each charge, then use the "particle info" entry under the "particle" menu to increase the charge to 2.
Field lines and equipotentials

Change the sign of the charge on the right. Understand?
Change the ratio of the charges. Understand?
This is important!

Click on the appropriate link to select Simulation A, B or C, then hit "play". A is pretty tame but make sure you understand it.

You should be able to answer these questions:
All sims: Are there charges present? Where?
Sim A: Which way is the electric field pointing?
Sim C: Note the motion of the charge when the simulation started. Replay it if needed. Now place the charge near C. Will it move toward or away from C?
Sim B: Same as above. The potential lines are a little off near the charges so I put this one last. The simulation is good enough, though.
Lightbulb test

A simple test of your understanding of series and parallel resistors and power.
Kirchhoff's Rules
1 2 3 4 

Four examples of the use of Kirchhoff's Rules. This is from the Virtual Labs
& Simulations
Electricity site.
Circuit builder

You can build and test any kind of circuit discussed in class using this. Here is an example that uses the circuit builder to illustrate RC circuits.
RC Circuits

Practice with a virtual circuit.
RC Circuits

Shows where the current and energy go in an RC circuit with a switch.
Digital circuit simulator

Java Logic Circuit Simulator Applet. We don't cover digital electronics, but here is something you can play with if you know a little about logic circuits. All of the basic gate types are available.
Charges in a magnetic field

Make sure you can control/predict whether the particle goes clockwise or counter clockwise.
Charge in combined E and B fields

Rotate the coordinate system with your mouse so you can see the 3-D motion.
Deduce the current

Use a compass to deduce the current direction through two wires. If you can do this, you understand magnetic field generation by a straight wire. Important!
Biot-Savart Law

Practice with the elements that make up the Biot & Savart Law.
Drag the wire

Faraday induction in action.
RLC circuit

A key example involving the three basic linear circuit elements: resistor, capacitor, inductor.



Spring & mass

Control your own spring and block. Set k=10 and start the block in motion by dragging it and releasing. A test: can you identify the meaning of the red arrow without reading through the description?
Spring & mass and

Gives you control over all parameters and allows you to monitor the position, velocity, acceleration, energy, etc.
Transverse and Longitudinal Wave

Make sure to read the directions below the demo.
Longitudinal Wave  good Longitudinal waves are harder to visualize. This demo helps connect particle motion (displacement, velocity, acceleration) to the wave motion. It's simple enough. Just make sure you understand the graphs you see.
Various Kinds of Waves

Make sure to look at the longitudinal wave. Try and focus on an individual particle in the wave. Compare it's motion to that of the wave. They're related, but they're different.
Superposition Using Pulses

I think it's easier to understand superposition when pulses are used, but is this simulation correct? Try this: Invert one of the pulses by left clicking below it. Watch. There will be a moment when the superposed wave (shown in black) is completely flat. Is energy conserved?
Superposition Principle for Waves

Superpose two arbitrary sinusoidal waves to get a standing wave. MAKE SURE TO READ THE INSTRUCTIONS. Is this method of getting a standing wave at all related to the class demo showing a standing wave using a rope tied at one end?
Superposition Principle for Waves II  ok Allows you to superpose two waves with full control over amplitude, direction, phase, etc. You can use this to demonstrate beats, standing waves and all other major phenomena discussed. The phase control is a little buggy, unfortunately.

Change the frequency and phase difference between two waves.
Various Kinds of Interference

The basic categories of wave interference discussed and illustrated!
Sonic boom good First, run the simulation and observe the Doppler effect. From its point of view, the wave emitter is running at a single frequency, but what to observers think that are: (a) behind, (b) ahead, (c) below the emitter. [Part (c) is the trickiest case.]

Second, note that initially the source speed is slower than the wave speed. Think of the source as a jet plane now. Increase the source speed by dragging its arrow until it matches the wave speed. Something important changes. Why do people talk about shock waves for this situation? Now, how can that explain a sonic boom? This is tricky. For an answer, try the next demo...
The location of a supersonic airplane 

Generating a sonic boom.

You'll have to think a little on this one. Read the instructions at the bottom so you under the controls first. Start with subsonic flight (ratio = 0.5). Make sure you understand the numbers that show up. Right-click to stop and restart the demo so you can see what is going on. At each point in its path (the white dots) the jet emits a spherical wave that expands in all directions. Think of the jet as a moving point source. The green and yellow lines just show the part of the wave emitted from a given white dot that is going in the right direction to reach the observer. Parts of the wave going in some other direction won't be heard and don't concern us here.

Now, switch to supersonic flight (ratio = 4.0).Note the change in the numbers that show up at the top. Waves emitted later reach the observer first!
Does the black line in this demo correspond to anything in the previous demo?
Why do the green and yellow lines come together in the funny way that they do?
The volume is related to the number of lines reaching the observer.

Try other ratios.

Uses your computer's audio system to illustrate the effect of changing the sound level by 3,6,10 and 20 dB.
Propogation of Electromagnetic Waves

Very simple, but helps with picturing how E, B, and the direction fit together. Picturing EM waves is trickier than you might think. Question: the graphs of E and B descibe how the fields change in time, but where? That is, fields are being plotted for what region of space: on the x-axis only, or off of it or some other axis?
Wave propagation, reflection/refraction
using Huygen's Principle

Pause and continue the demo so you can follow everything that happens. Yes, it's true. Simple reflection and refraction is a more complicated process than you might at first think.
Wave propagation using Huygen's Principle II very
Another one, but more in the style of a tutorial. Hit "Start Simulation" to start the demo. After each simulation, hit "Next Step".
Ripple Tank  excellent This is one of the best of this type that I've seen. Two windows will come up. One contains the applet and the other contains directions. It's amazing what you can do. Note that if you click in the tank, you set off ripples as if you had dropped a pebble in it.
Reflection and Refraction

Sends a beam through an interface under your control. Illustrates reflection, refraction, total internal reflection.
A fish's view

Fish have rights too, I suppose. Try making the object very wide and placing directly over the fish.
Physics of rainbows

Also illustrates the idea of dispersion: different colors have different indices of refraction.Can a single raindrop produce a rainbow, even if very weak, for an observer on the ground?
Color  ok So what is the difference between mixing light and mixing paint?
Thin Lens

Try this! Automatic ray tracing, using a bundle of rays or the three special rays, as you adjust the object. Place the object on the focal plane and to either side of it.
Thin Lens II good The previous one is better, but here's another that provides automatic ray tracing using the three special rays we've discussed in class as you adjust the object.
Lens Problem #1
Lens Problem #2

Use these to test your understanding of lenses. See if you can find a position for the lenses that makes the answer to the question obvious.
If you can't solve these, see me!
Don't forget to hit "Start" at the bottom of the page.
Two-Slit Interference - Young's Experiment

Shows the wave train from each slit and how the interferences changes across the viewing screen. (Requires a flash player.)
Single Slit Diffraction 
Double Slit Diffraction

If you're just starting to learn the subject, this illustrates the basic phenomena.
If the exam is near, you're in trouble if you can't predict what the result of adjusting the controls will be!
Interference of waves from two point sources  good Place the two point sources on top of each other and look at the result. Then move one of them sideways in small steps and observe the change. You should be able to explain what you see. What happens when the two sources are 1/2 a wavelength apart? How about a full wavelength?
Interference of waves from two point sources II

Similar to the above. You can use this to explain what you saw in the previous one. However, it's harder to interpret until you get the hang of it. Here the essential point: if you see a black line on top of a white line, there's desctructive interference. If you see two lines intersection that have the same color, there's constructive interference. Also, try using "No pattern" at first.
The following demos cover aspects of modern physics: Special Relativity and Quantum Mechanics.
They're, perhaps necessarily, a little harder to understand but worth the effort.
Michelson-Morley Experiment

Illustrates what is expected from the experiment if light actually travels in a medium.
Space-Time Lab

Shows you moving rods, clocks and more from the point of view of an outside observer and observer moving with the rod or clock. Make sure to set the velocity slider at the top. Also, try out the JAVA TA if you'd like a discussion.
Young's Experiment With Electrons  good A simulation of what you would see. This is important. Each individual electron impacts and registers as a single dot. Let it run for awhile. The problem is the pattern formed after many electrons have hit.....
Finally, notice how the graph isn't smooth. That "noise" is a fundamental part of how our world works.
Energy Well  good Gives you practice working with energy wells, without having to worry about quantum mechanics. It uses a cart with a pair of magnets on it and allows you to place magnets outside the car.
Quantum States in a Potential Well  good Drag the corners of the potential well and note how the states change. Both their position and number are important. Does a potential well have to have at least one bound state? Is it possible for one to have infinitely many states?
Quantum States in a Potential Well II  very
Similar to the previous one, but shows the wave function too. Select "show eigenstates" and "single well" to start off with.
Probability Illustrator  good Draw an arbitrary wavefunction using the mouse and then see what probability distribution results. You can also measure the probability using the green arrow heads at the bottom.  You should definitely know how to get a probability of 1 and what that means. If you don't, ask me.



Distance versus Displacement

Compare these concepts using a journey of your choice.
One-D Motion

Study displacement, velocity, and acceleration and how they relate to each other.
Traffic Control

Get a feel for constant acceleration.
Relative Motion

Travel down a river from several points of view.
Vector Test

Practice with instant feedback.
Free-body force diagram

Practice making one.
Newton's Third Law

Poses conceptual questions.
Projectile Motion

Study how v, a, and their components change.
Projectile Motion II

Classic test of your insight on free fall.
Projectile Motion III

Yes, this subject is important enough to merit a third demo.
Two Balls, a Table, and Some String

This is a standard problem for introductory physics classes studying centrepital acceleration. Make sure you understand it.

A lesson in mechanical advantage. Make sure you understand the value of the tension everywhere and the role it plays.
Blocks Stacked on a Table

This is a standard problem on the friction force. Make sure you understand this one too.
Bouncing Ball

This was written by a student taking a course like this one. He notes that the demo has some bugs in it which result in unphysical behavior. Can you identify what that behavior is? Hint: try some "special" cases where the answer should be especially simple.
Orbits and Falling

Do you really understand why they say astronauts in orbit are in free fall? (Incidentally, this demo uses the same approach that Newton took when he tried to understand orbits.)
A Sun and Planet

Shows how each orbits the center-of-mass. Make sure to select different perspectives and various masses.
Kepler's Orbits

More detail on what an orbit is. Beyond what we will cover in class, but interesting.
Center of Gravity

Turn on all options so you can see the center-of-gravity of each component.
1-D Collisions

See how momemtum is conserved independent of the oberver's (that is, your) inertial frame of reference.
2-D Collisions

Make sure to do all the things described, in order.

Connects x,v,a with their angular equivalents.
In which direction will it roll?

Test your intuition on angular momentum.



Other Lists Of Links To Demonstrations

Fu-Kwun Hwang's Page Another Virtual Laboratory, frequently expanded and updated.
Interactive Physics Good circuit demos here. Also, some E&M including diffraction and optics.
Surendranath's Page A number of his applets are in the 132 and 133 lists.
Fowler's Physics Applets Small collection of applets used in a class sequence similar to our 131-2-3.
Physlets Covers material in 132 and 133. This site has grown and become a good resourse.
M. Casco Assoc. A digital textbook on mechanics. It ends with what might be an interesting discussion of how space can have structure.
Java Applets On Physics Small but nice collection by Walter Fendt.
Quantum Physics Online Good demos, although most are more appropriate for a class on quantum.
Visual Quantum Mechanics From the PERG in Kansas. Includes some wave mechanics demos in the making waves section.
Online resources for physics teachers Wide range of categories with many links, but no effort to describe the links.
Virtual Labs & Simulations  It's huge link list.
Paul Falstad's applets Easily one of the best applet writers out there, in my opinion.
Contemporary College Physics Simulation Library Mostly Hwang's work.

The material below is scratch space to help me organize this page.
There is not necessarily any connection to your class here.

Unsorted Or Under Consideration
Electron Interference
conservation of energy
gallery of electromagnetism
Rami Arieli: "The Laser Adventure" Java Applets List
Physics 2000 Applets from the University of Colorado (including applets on basic E&M as well as optical cooling and BEC)
Physics Web Resources
Stan Durkin's applet list for his 11x classes 
Applets from Harry S. Truman college
Some applets including ones on quantum mechanics, chemistry, and laser cooling 
The Continuity Equation Illustrated using a pipe with an adjustable constriction.
Falling Into A Black Hole This is advanced, but fun.


Replaced By Better Ones
Interference of waves from two point sources II

Gives you a virtual ripple tank. More quantitative than the previous one.
Concept of Space and Time in Special relativity

Allows you to compare events seen from two different inertial frames. [This is a little tricky. The oscillating dots are each a light pulse going between mirrors as in class.]
The Twin Paradox

Tricky, but that's hard to avoid.


Broken or Otherwise Defunct
Electric field probe You are given a probe that graphically indicates the electric field for some simple charge distributions. might be a replacement, but the embedded javascripts don't seem to run.
Find the hidden charges This is a nice test. If you can answer the questions following, you've acquired good insight on the connection between field and charge.

Select the length and watch it oscillate.
Transverse Wave and Longitudinal Waves

Use the start and stop buttons to see the wave evolve. Longitudinal waves can be tricky to think about so make sure to look at those.
Longitudinal Waves

Longitudinal waves are harder to visualize than transverse waves. This may help.
Another virtual ripple tank

The display is messy. Use the buttons to view one feature at a time.
The Virtual Laboratory From TIPTOP (The Internet Pilot to Physics). This is an enormous list.