tag:techtv.mit.edu,:Array/219056460 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/219033980 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/219011480 2008-06-26 16:47:33 -0400 MIT Department of Physics Technical Services Group <p>A long length of wire is suspended horizontally between the poles of a magnetron magnet. When a large current from a 12V storage battery is passed through the wire, the wire jumps out of the magnetic field. When the direction of the current is switched, the wire jumps the opposite direction.</p><p>The magnetron magnet in this demonstration was originally used in MIT's groundbreaking research developing radar during and after World War II. Microwave emitting <a href="http://en.wikipedia.org/wiki/Cavity_magnetron">cavity magnetrons</a> need strong magnetic fields, which were often created by powerful permanent magnets like the one used in this demo. </p> 37