# Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know  ## Metadata - Author: [[Richard A. Muller]] - Full Title: Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know - Category: #books - Document Tags: [[favorite]] [[physics]] - Summary: The book explains essential physics concepts that every leader should know, including heat, temperature, and radioactivity. It discusses how different forms of radiation, like gamma rays and x-rays, have high energy and can cause significant effects, such as cell destruction. The text also highlights the importance of understanding nuclear energy and its potential applications, including in atomic bombs. ## Highlights - In fact, heat *is* kinetic energy, the kinetic energy of molecules.[1](#c02-ftn1) Your hands feel warmer because, after rubbing, the molecules are shaking back and forth faster than they were prior to your rubbing. That’s what heat really is: the shaking of atoms and molecules, rapid in speed, but microscopic in distance. ([View Highlight](https://read.readwise.io/read/01jtvqes6zkcq0npepzsyqmm5j)) - the typical velocity of shaking is about the same as the speed of sound, about 700 miles per hour, 1000 feet per second, or 330 meters per second. That’s fast. Yet the particles (at least in a solid) can’t travel very far. They bump into their neighbors and bounce back. They move fast but, like a runner on a circular track, their average position doesn’t change. ([View Highlight](https://read.readwise.io/read/01jtvy563zav0h37whpcve571n)) - Atoms are too small to be observed with an ordinary microscope. Their size is about 2 × 10–8 cm = 2 × 10–4 microns.[4](#c02-ftn4) If you move across the diameter of a human hair (typically 25 microns), you will encounter 125,000 atoms from one side to the other. A red blood cell (8 microns across) has about 40,000 atoms spanning its diameter. Some molecules are so large (such as DNA) that they can be seen under a microscope, although the individual atoms in the molecules can’t be resolved. ([View Highlight](https://read.readwise.io/read/01jtvyea8htdpwrgqdxz96etm8)) - Even though you can’t see atoms, you can see the effect that their shaking has on small, visible particles. With a microscope, you can see the shaking of tiny bits of floating dust (1 micron in diameter). This phenomenon is known as *Brownian motion*.[5](#c02-ftn5) The shaking comes from the dust being hit on all sides by air molecules, and if the dust is sufficiently small, this bombardment does not average out.[6](#c02-ftn6) ([View Highlight](https://read.readwise.io/read/01jtvy7c5htm8k0tdbvc6pk41g)) - Is it a coincidence that the speed of molecules is approximately the speed of sound? No—sound travels through air by molecules bumping into each other. So the speed of sound is determined by the speed of molecular motion. Sound traveling through a gas cannot move faster than the velocity of the gas molecules.[7](#c02-ftn7) ([View Highlight](https://read.readwise.io/read/01jtvyfvas7d2627dcgtsx1pyn)) - You can easily measure the speed of sound yourself. One way is to watch someone hit a golf ball, chop wood, or hit a baseball. Notice that you see the event before you hear the noise. That’s because the light gets to you very quickly, and then you have to wait for the sound. Estimate your distance to the person, and estimate how long it takes for the sound to reach you. If the distance is 1000 feet, the delay should be about 1 second. ([View Highlight](https://read.readwise.io/read/01jtvyhqbtgrzy8qz66kj3bdrc)) - When I was a child, and afraid of thunder and lightning, my parents taught me a way to tell how far away the sound and light was coming from. For every 5 seconds between the lightning flash and the thunder, they said, the lightning was 1 mile away. ([View Highlight](https://read.readwise.io/read/01jtvyka2j2t14w97c2wqd88nr)) - The molecule known as DNA, which carries our genetic information, can contain billions of atoms.[3](#c02-ftn3) ([View Highlight](https://read.readwise.io/read/01jtvqtty9zah1jhc5ycyh6vqc)) - In all materials, the molecules are constantly shaking. The more vigorously they shake, the hotter the material is. When you rub your hands together, you make the molecules in your hands shake faster. ([View Highlight](https://read.readwise.io/read/01jtvqvf417rv9526qpgz01n67)) - **Remember:** The speed of light is about 1 foot in 1 computer cycle (1 ns). ([View Highlight](https://read.readwise.io/read/01jtvypkfn4mz63tg0y1x0esqy)) - The average speed of the molecules that compose this book is the speed of sound, but they are all moving in random directions. Suppose that I made them all move in the same direction. Then the entire book would be moving at the speed of sound, 720 miles per hour. Yet the total energy would be exactly the same. This example illustrates the enormous energy that is contained in the heat of ordinary objects. Unfortunately, it is often not possible to extract that energy for useful work. ([View Highlight](https://read.readwise.io/read/01jtvyqw9s11r65xd2fzerp0bm)) - There is no good way to change the directions of the shaking so that all the molecules move together. Yet we can do the opposite. When an asteroid hit the Earth 65 million years ago, all the molecules were initially moving at 30 kilometers per second in the same direction. After the impact, the directions were all different. ([View Highlight](https://read.readwise.io/read/01jtvyrkqbnnzqf52ryyjd1rez)) - When kinetic energy is turned into heat, we can think of this process as coherent, regular motion becoming randomized. The molecular energy changes from being neatly “ordered” (all molecules moving in the same direction) to being “disordered.” The term *disorder* is very popular in physics. The amount of disorder can be quantified, and that value is given the name *entropy*. ([View Highlight](https://read.readwise.io/read/01jtvys7hahfmjch4rw438vq8c)) - In [chapter 9](#BE6O0-5ef3d5233b8b4e0cb7870b1681d864b7), I’ll talk about a device for seeing in very low light that had such a cooling system attached. But too much cooling can cause the device to cease operation, since a transistor (discussed in [chapter 11](#DB7S0-5ef3d5233b8b4e0cb7870b1681d864b7)) actually depends on the fact that room-temperature electrons have some kinetic energy. Without that kinetic energy, the electrons become trapped and electricity doesn’t flow. If you cool a transistor, and remove that energy, the transistor no longer functions. ([View Highlight](https://read.readwise.io/read/01jtvzd0w1yx9pvvkpactvaj0a)) - The temperature increases when the average shaking energy of its molecules is greater. (We use the word *average* because at any given instant, some of the molecules may be moving faster than others, and some slower, just like dancers on a dance floor.) ([View Highlight](https://read.readwise.io/read/01jtvzgbdfef5nzrvvhg273y95)) - Here is a surprising consequence of what I just said. Suppose that two bars, one made of iron and the other of copper, have the same temperature. Then their molecules must have the same kinetic energy, on average. Will the iron molecules and the copper molecules have the same average speed? The surprising answer is *no*. The iron molecules, which are lighter (see [figure 2.1](#fg2.1)), will be shaking faster, on average. In [chapter 1](#3Q280-5ef3d5233b8b4e0cb7870b1681d864b7), I said that kinetic energy is given by *KE =* 1/2 *mv*2. Copper and iron have different molecular masses *m*. So the heavier copper molecule must have a smaller velocity *v* in order to have the same kinetic energy *KE*. ([View Highlight](https://read.readwise.io/read/01jtvzns5t6tmtpd7mckqg9dzp)) - The key discovery that makes temperature a really useful idea is the simple fact that two things that touch each other tend to reach the same temperature. That is why a thermometer gives you the temperature of the air—because it is in contact with the air, so it gets to the same temperature. ([View Highlight](https://read.readwise.io/read/01jtvzm4gc6az3jw1vx4ppvn98)) - The fact that objects in contact tend to reach the same temperature was such an important observation that it was given a fancy name: the *zeroth law of thermodynamics*.[9](#c02-ftn9) ([View Highlight](https://read.readwise.io/read/01jtw11j7mtaafjjp08xnpr2fs)) - The “flow” of heat is actually the sharing of kinetic energy. Heat (kinetic energy) is given up by the hot material to the cold one. The flow stops only when both materials have the same temperature. This means that if you put a bunch of things in the same room and wait, eventually they will all reach the same temperature. ([View Highlight](https://read.readwise.io/read/01jtvzqzwbjy46fntf0ebgcc77)) - The element hydrogen is, by far, the most abundant element in the Universe. Hydrogen atoms make up 90% of the atoms in the Sun. The same is true for the large planets of Jupiter and Saturn. Yet in the atmosphere of the Earth, hydrogen gas is virtually absent. ([View Highlight](https://read.readwise.io/read/01jtvzv8ben5fnkkd3fmk82jqv)) - Hydrogen in the atmosphere of the Earth would have the same temperature as the nitrogen and oxygen. Therefore, the molecules of hydrogen have the same kinetic energy, on average. But since hydrogen is the lightest element (its atomic weight is only 1/16 that of oxygen), it must have a higher velocity. Since energy depends on the square of the velocity, the velocity must be a factor of 4 larger (so the square is 16). This high average velocity turns out to be enough for the hydrogen to escape from the Earth like a rocket The Sun and Jupiter have much stronger gravity than the Earth, so they kept their hydrogen. ([View Highlight](https://read.readwise.io/read/01jtw023kg2dzmy3ezc0fjmb2b)) - The Earth lost its hydrogen gas because our gravity is too weak. ([View Highlight](https://read.readwise.io/read/01jtw02r2htbhcrgjhha0jgqdb)) - Stars are very hot, and molecules in space are very cold. Eventually, the stars will stop burning, and eventually everything in the Universe may reach the same temperature. ([View Highlight](https://read.readwise.io/read/01jtw09p8jnnbde08zrf0g7yzt)) - The scales are defined such that the freezing point and melting of water is 32°F and 0°C, and the boiling and condensation point of water is 212°F and 100°C.[13](#c02-ftn13) ([View Highlight](https://read.readwise.io/read/01jtw0b9qhttx0ae0th9cdh9n0)) - A change of 1 C is a change of 9/5°F = 1.8°F ≈ 2 F ([View Highlight](https://read.readwise.io/read/01jtw0nk8jpd2mhd9hkcqm2ysr)) - At room temperature, the kinetic energy of the atoms in the air is identical to the kinetic energy of the atoms in this book. ([View Highlight](https://read.readwise.io/read/01jtw1dmfph3q9v6a0p38ssrja)) - You can convert from the Kelvin scale to the Celsius scale by subtracting 273:  ([View Highlight](https://read.readwise.io/read/01jtw1d5tqvf81s3m45zhhtrsy)) - On 1 February 2003, the *Columbia* space shuttle broke apart in flames as it reentered the atmosphere, killing all seven astronauts on board. The space shuttle always generates enormous heat when it reenters the thicker parts of the Earth’s atmosphere. That’s because it has very large kinetic energy, and to slow down (so that it can land), it must get rid of that energy. ([View Highlight](https://read.readwise.io/read/01jvbbta909pdr65fbkj19q5zb)) - **High temperatures:** Here’s a little trick you might find helpful. Suppose that an object (such as a meteor, or the interior of the Sun) has a temperature of 100,000 C. How hot is it in K? The answer is 100,273 K. That looks pretty close to 100,000. They differ by only 0.27%. Here is a useful rule: When temperatures are really high, then the temperature in C is approximately the temperature in K. ([View Highlight](https://read.readwise.io/read/01jvbc2wf2w4bbpp1y70xdw89y)) - When the atoms in a solid heat up (i.e., they move faster; i.e., their velocity increases; i.e., they get more kinetic energy), they tend to push their neighbor atoms farther away. The effect is small, but important—most solids expand a little bit when heated. ([View Highlight](https://read.readwise.io/read/01jvbc4ptdq6v40e76d71z96xd))