Lecture-demo materials
3D computer demos
Mechanics lecture-demo programs written in VPython
E&M lecture-demo programs written in VPython
For VPython computational modeling activities carried out by students, see Instructor resources.
Videos
After the new 3rd edition of the textbook was completed, Ruth Chabay created a new approach to the Momentum Principle that may prove useful in helping students understand what it predicts. Here is a video of her presentation on A New Approach to the Momentum Principle to students as a review at the end of the Fall 2009 semester at NCSU (Quicktime, 640 by 480, 45 MB zip file).
Ball-and-spring
model of a solid (Quicktime,
640 by 480, 21 MB zip file)
Ball-and-spring
model of a solid (Quicktime,
320 by 240, 7 MB zip file)
For the following, if Quicktime is installed you can play these movies in the browser, or you can download them with right-click on Windows, ctrl-click on Macintosh.
Two pucks pulled by the same force (Quicktime)
Observing surface charge on a high-voltage circuit (Quicktime)
It is possible to see mechanical effects of surface charge in a high-voltage
circuit. In an ordinary circuit with a 1.5 volt battery, the electric field
in the wires is only a few volts per meter, and the amount of surface charge
buildup sufficient to produce such small fields is so small that it is
difficult to see mechanical effects of that surface charge. (Notice that
electrostatic fields can be very large: the field required to make a spark
in air is about three million volts per meter.)
The video shows a circuit driven by a 10,000 volt power supply. The power supply is arranged so as to apply +5000 volts to one end of a chain of four resistors, and -5000 volts to the other end. The electric field in each resistor is large, so the gradient of surface charge is large along the circuit, with a large positive surface charge at the right end of the resistor chain and a large negative surface charge at the left end. Given the symmetrical arrangement, we expect zero surface charge on the wire at the center of the chain of resistors.
We discharge a hanging piece of aluminum foil and bring it near the -5000 end of the circuit. We see the foil attracted to the wire, then repelled. The foil was polarized, attracted, then charged negative by contact. Each time we try this, we first touch the foil to distribute any charge all over the body, so the foil is neutral. We rub a plastic pen, charging it negative, and bring it near the foil, which is repelled. This shows that the foil did charge negative by contact as expected.
Next we try the +5000 volt end of the chain of resistors. We again see that the neutral foil is attracted due to polarization, charges by contact, then is repelled. We see that the foil is now attracted by the negative pen, showing that it charged positively as expected.
When we bring the foil near the center of the chain of resistors, we see as expected that nothing happens, because the surface charge there should be zero.
