by Walter Lewin
* Be careful—never look at the Sun.
* It happened to Lise Meitner, who helped discover nuclear fission; Rosalind Franklin, who helped discover the structure of DNA; and to Jocelyn Bell, who discovered pulsars and who should have shared in the 1974 Nobel Prize given to her supervisor, Antony Hewish, for “his decisive role in the discovery of pulsars.”
* I have assumed here that the force on the charged particle due to gravity is so small that it can be ignored.
* 1 kilogram is about 2.2 pounds.
* The Royal Society recently posted a digital image of Stukeley’s manuscript online, which you can find here: http://royalsociety.org/turning-the-pages/.
* If you ever want to use this value, make sure that your masses are in kilograms and that the distance, r, is in meters. The gravitational force will then be in newtons.
* If the mass of the string cannot be ignored, and/or if the size of the bob cannot be treated as a point mass, then it is no longer a simple pendulum. We call it a physical pendulum and it behaves differently.
* Remember, all you scientists, I’m using common rather than technical language here. Even though a kilogram is in fact a unit of mass, not weight, it’s often used for both, and that’s what I’m doing here.
* If you want to see my photo online, click on the website’s Archive and go to 2004 September 13. See text above for the general URL.
* If you want to use this equation at home, use 9.8 for g and give h in meters; v is then in meters per second. If h is 3 meters (above the floor), the object will hit the floor at about 5.4 meters per second which is about 12 miles per hour.
* For simplicity I have used 10 meters per second for g; we do that often in physics.
* For rotating black holes the event horizon is oblate—fatter at the equator—not spherical.
* Little did I know at the time that Jan and I would become very close friends and that we would coauthor about 150 scientific publications before his untimely death in 1999.
* This acceleration, by the way, is 0.18 percent lower at the equator than at the poles—because Earth is not a perfect sphere. Objects at the equator are about 20 kilometers farther away from the Earth’s center than objects at the poles, so at the equator g is lower. The 9.82 is an average value.