tag:techtv.mit.edu,:Array/219258560 2008-10-10 14:24:44 -0400 MIT Department of Physics Technical Services Group Two carts are connected together on an air track with a spring. Under bright lights you can see the coupled oscillation of the carts back and forth, but under black lights you can see that the center of mass moves at a constant velocity. 103 tag:techtv.mit.edu,:Array/219237780 2008-06-20 15:47:45 -0400 MIT Department of Physics Technical Services Group <p>A small glass tube, held by copper wire, is placed in series with a light bulb. The glass acts as an insulator at room temperature, meaning the current cannot flow between the copper wires. This leaves an open circuit and the light bulb does not light up. Touching a conductor across the copper wires (with a metal screwdriver for instance) does complete the circuit because it allows current to flow.</p><p>However, when glass is sufficiently heated by a torch it becomes an ionic conductor. Ionic bonds in the glass are broken, allowing the charge carrying ions to move freely. Thus, when the glass is melted the current can flow, which closes the circuit and lights the bulb. </p> 72 tag:techtv.mit.edu,:Array/219218820 2008-06-06 11:36:25 -0400 MIT Department of Physics Technical Services Group An RF transmitter is connected to a long antenna, emitting radio waves. A dipole antenna with a light bulb between its elements acts as the receiver. When the receiving antenna is parallel to the transmitter, the radio waves are absorbed, creating a current in the antenna and causing the bulb to glow. When perpendicular, no current is created, and the bulb does not glow. 57 tag:techtv.mit.edu,:Array/219199920 2008-06-20 16:53:07 -0400 MIT Department of Physics Technical Services Group <p>A light bulb is placed in series with two copper plates immersed in de-ionized water. Touching the plates closes the circuit, lighting the bulb.</p><p>When kosher salt is dropped into the de-ionized water, the salt dissolves, causing ions to be dispersed throughout the liquid. The free ions allow current to flow through the water, which completes the circuit and lights the bulb.</p><p>Most water we encounter in everyday life is not de-ionized and contains impurities with dissolved ions. This is why we know water as a good conductor, and why we shouldn't use electronic devices around a bathtub, for example.</p> 54 tag:techtv.mit.edu,:Array/219181000 2008-09-02 15:54:18 -0400 MIT Department of Physics Technical Services Group A ball is dropped in front of a meter stick and lit by a strobe light. A long exposure photograph captures the position of the ball at each evenly spaced flash of light. The acceleration of the ball can then be measured from the photo. <br><br> Note that the frame rate of the video capture (30fps) is quite close to the strobe rate (15Hz). This is why the strobe flashes in the slow motion video don't appear to be exactly evenly timed. <br><br> See the <a href="http://www.flickr.com/photos/physicsdemos/3174207211">final image</a> on Flickr. 42 tag:techtv.mit.edu,:Array/219162040 2007-12-28 10:14:37 -0500 Doc Edgerton Films Watch this silent film with descriptive boards of a demonstration on the velocity of light as performed by Doc Edgerton and some of his assistants. 92 tag:techtv.mit.edu,:Array/219141260 2009-01-21 14:43:14 -0500 MIT Department of Physics Technical Services Group A light bulb is connected in series with a coil of very fine copper wire and a DC power supply. The voltage is adjusted so that the bulb glows dimly. When the coil is immersed in liquid nitrogen the resistance of the wire decreases causing the current to increase and the bulb to glow brightly. 71 tag:techtv.mit.edu,:Array/219122360 2009-04-16 11:06:25 -0400 MIT Department of Physics Technical Services Group A laser is directed at an adjustable single slit and then a pinhole and the resulting diffraction patterns can be seen on a screen. <br><br> A laser directed at two slits spaced closely next to each other creates an interference pattern within the diffraction pattern. Shining lasers of different wavelength light shows how the wavelength affects the interference and diffraction patterns. 146 tag:techtv.mit.edu,:Array/219103360 2009-06-03 15:26:02 -0400 MIT Department of Physics Technical Services Group Odd-shaped objects with their centers of mass marked by orange paint are thrown. While the objects appear to follow very wobbly trajectories when viewed under bright lights, under black lights you can see that their centers of mass travel in smooth parabolas. <br><br> Then center of mass is not necessarily in the center of an object, as demonstrated by the last object in the video (a weighted disk). 91 tag:techtv.mit.edu,:Array/219084460 2009-06-10 14:04:53 -0400 MIT Department of Physics Technical Services Group Two pucks of the same mass are slid at each other on an air table, and their resulting collisions demonstrate conservation of momentum. Notice on the first collision, for example, that when a moving puck hits a stationary puck dead-on, that the second puck leaves with the same velocity as the first, and the first puck stops moving completely. 80