## 5 Fascinating Physics Facts

Paul J. Nahin shows that physics is all around us in his new book, In Praise of Simple Physics. Nahin takes the reader step by step through a variety of everyday examples, proving that you don’t need an advanced degree to appreciate the math behind a speeding car, a falling object, or the rotation of the planets. For instance:

1. The Sun’s gravitational force upon Earth is 180 times larger than the Moon’s gravitational force upon Earth (p. 45), but lunar tides are larger than solar tides because the Sun is so much further away than the Moon (p. 48).

2. Saturn’s rings are believed to have been caused by tidal forces due to gravitational variation. Long ago, a moon of Saturn got too close to the planet and was pulled apart—the fragments make up the rings (p. 49).

3. Gravity and centripetal acceleration caused by the Moon create two tidal bulges on Earth—one directly below the Moon and the other on the far side of the Earth opposite the first bulge. The Moon’s gravitational pull on the two tidal bulges produces a net counter-rotational torque that tends to reduce the Earth’s rotational speed. The result is that the length of a day on Earth is continually increasing by about 2 milliseconds per century. Assuming that this rate of increase has been in effect for the last 2,000 years, then the day Julius Caesar was assassinated in 44BC was shorter in duration, compared to yesterday, by about 40 milliseconds (p. 53).

4. Physics can be funny! What do you get when you cross a mosquito with a mountain climber? A biologist would say, “nothing, because that’s impossible to do,” and a mathematician would be able to prove why. In vector mathematics there are two different ways to multiply two vectors together: the dot product (which produces a scalar result), and the cross product (which produces another vector). Each starts with two vectors. While a mosquito is, in fact, a vector of disease, a mountain climber is a scalar and you cannot cross a vector with a scalar (p. 66).

5. The center of mass is the point at which we can imagine the entire mass of the object is concentrated as a point mass. If you stack books on top of each other with each staggered exactly halfway across the one beneath it (at the center of mass) and off the edge of the table, the stack will not fall (p. 97).

If any of these facts have you scratching your head and you want to know more, pick up a copy of In Praise of Simple Physics for detailed explanations of the math behind each of these—and many more!

If you would like updates of new titles in math or physics, subscribe to our newsletter.

## In Celebration of Mathematicians

This week San Diego, California is home to the largest mathematics meeting in the world. Hosted by the Mathematical Association of America (MAA) and the American Mathematical Society (AMS), the 2013 Joint Mathematics Meeting is more than just panels and presentations—it is a mass gathering of people who are passionate about mathematics.

Mathematicians come from diverse backgrounds, maintain varying interests, and have their own unique journeys. In Fascinating Mathematical People: Interviews and Memoirs, Fern Hunt describes what it was like to be among the first black women to earn a PhD in mathematics, Harold Bacon makes trips to Alcatraz to help a prisoner learn calculus, and Thomas Banchoff, who first became interested in the fourth dimension while reading a Captain Marvel comic, relates his fascinating friendship with Salvador Dalí and their shared passion for art, mathematics, and the profound connection between the two. But whether they view mathematics as reason, art, or something else, all mathematicians are in search of truth.

This week is not only an endeavor in furthering the pursuit of knowledge, but a celebration of the gifted mathematical intellectuals who shape society, culture, and our awareness and understanding of ourselves and the world in which we live. Browse our website or latest mathematics catalog to see more by and about mathematicians, such as Paul J. Nahin’s The Logician and the Engineer: How George Boole and Claude Shannon Created the Information Age. If you’re at the Joint Mathematics Meeting, you may even visit us at booth 311. As Underwood Dudley wrote in “What Is Mathematics For?” included in The Best Writing on Mathematics: 2011 (The Best Writing on Mathematics: 2012 also available.), “What mathematics education is for is not for jobs. It is to teach the race to reason,” and we’ve all got room to learn.