tag:techtv.mit.edu,:Array/291435700 2008-07-18 11:31:42 -0400 MIT Department of Physics Technical Services Group <p>A 100 uF oil-filled capacitor is charged to 3 KV. This takes approximately 15 minutes, creating a charge on the capacitor that could be lethal. The capacitor is then discharged through a 12" length of 30 gauge bare iron wire.</p><p>When the high voltage current flows though high resistance wire, the bonds between iron molecules are shattered, resulting in a loud bang, a shower of sparks, and a cascade of wispy filaments floating through the air.</p><p>Not all of the charge on the capacitor is disharged through the wire, so a shorting bar must be used to release the remaining charge. </p> 121 tag:techtv.mit.edu,:Array/291371380 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/291320940 2008-07-11 16:51:41 -0400 MIT Department of Physics Technical Services Group <p>An cathode ray tube (CRT) television is connected to a video camera. When a strong magnet is brought close to the television screen, the image becomes warped and discolored.</p><p>While many new televisions use flat screen technology, older CRTs produced images by firing electron guns (one red, one green, one blue) through the television body onto the back of the screen. When a magnet is brought close to the screen, it deflects the paths of the electron beams and distorts the picture. A strong enough magnetic field can even create a hole in the electron beams, causing a black spot on the picture. </p><p>This TV has been subject to many magnet encounters, which has permanently damaged the picture. </p> 96 tag:techtv.mit.edu,:Array/291295620 2008-08-27 16:48:12 -0400 MIT Department of Physics Technical Services Group <p>A bicycle wheel is suspended from one of end of its axie by a rope, and spun up by hand. The wheel's axle is then placed horizontally and the free end of the axle processes about the supported end. </p><p>The gyroscope seems to defy gravity because the torque created by the spinning wheel counteracts the torque due to gravity. Read more about gyroscopes <a href="http://en.wikipedia.org/wiki/Gyroscope">here</a>. Gyroscopes have been used through history for varied uses such as stabilizing spacecraft or for guidance systems on ships and missiles.</p> 89 tag:techtv.mit.edu,:Array/291267620 2008-09-02 10:20:19 -0400 MIT Department of Physics Technical Services Group <p>A stuffed monkey is suspended from a rod at one end of a lecture hall by an electromagnet. A golf ball gun aimed directly at the monkey cuts power to the electromagnet when fired. Thus, the monkey begins falling at the same instant the gun fires the golf ball. The projectile and target meet in mid air.</p><p>Intuitively one might think that the ball will go over the monkey's head due to its fast speed. However, gravity accelerates all objects downward at the same rate, meaning the monkey and the ball will meet at exactly the same point. If the ball was shot even faster, it would still hit the monkey, but higher above the ground. </p><p>No animals were harmed in this demo. </p> 77 tag:techtv.mit.edu,:Array/291242540 2008-08-28 14:21:12 -0400 MIT Department of Physics Technical Services Group <p>A wooden ball is attached to the rim of a spinning wheel. The ball is held in place by a string. When the spring is cut, the ball flies in a straight tangent to the wheel.</p><p>In the camera's frame of reference, the ball constantly accelerates around in a circle due to the centripetal force pulling it inwards. When the string is cut, the acceleration stops, and the ball flies away in a straight tangential line. When the string is cut in the rotating frame of reference, a ficticious force (centrifugal force) accelerates the ball. </p> 79 tag:techtv.mit.edu,:Array/291217380 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/291192300 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/297963500 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/295781400 2008-09-09 14:53:31 -0400 MIT Department of Physics Technical Services Group A can of spray paint is attached to a spring oscillator. A roll of paper is run past the oscillating can. The result is a <a href="http://en.wikipedia.org/wiki/Sine_wave">sine wave</a> on the paper. 51