# Guesstimation 2.0: Solving Today's Problems on the Back of a Napkin

Lawrence Weinstein
Pages: 376
https://www.jstor.org/stable/j.cttq94ww

1. Front Matter
(pp. i-vi)
(pp. vii-x)
3. Acknowledgments
(pp. xi-xii)
4. Preface
(pp. xiii-xviii)
5. Chapter 1 How to Solve Problems
(pp. 1-10)

Because we need to know an answer so we can decide what to do. If we’re deciding whether to drive to Virginia Beach for the weekend, we need to estimate how long it will take. If we’re deciding whether to get a solar panel on our new car, we need to estimate how much gas it will save. If we’re deciding between paper and plastic, we need to estimate how much plastic is in the bags we use each year. All these questions (and many more) lead to actions. If the drive is too long, we won’t go to Virginia...

6. Chapter 2 General Questions
(pp. 11-62)

Here are some of life’s important questions, ranging from the total length of all our toilet paper through the literary efforts of a million monkeys to the amount of pee in our swimming pool. We’ll start slowly by estimating length, then area, then volume, and then more intricate questions.

If all of the toilet paper used in the United States in an entire year were rolled out, how far would it stretch?

ANSWER: To estimate this, we need to break it down into how much toilet paper each American uses daily, how many Americans there are, and how many days...

7. Chapter 3 Recycling: What Really Matters?
(pp. 63-100)

We are constantly urged to recycle in order to “save the Earth.” How much effort should we really put into recycling? Given our limited resources (including especially mental effort and available attention), where should we put our environmental efforts?

Note that there are two schools of thought about environmental and other moral efforts. The first school claims that if we can just train everybody to be environmentally conscious, then everybody will recycle, drive smaller cars, bicycle to work, and generate their own electricity during gym workouts. The second school claims that humans perform only enough “good deeds” to see themselves...

8. Chapter 4 The Five Senses
(pp. 101-138)

We view the world through our senses. Our eyes can see at noon and at midnight. Our ears can hear a whisper and a rock concert. Our senses have a remarkable range and sensitivity. Let’s explore that in this chapter.

What is the maximum amount of light that our eyes can tolerate, even briefly?

ANSWER: We need to estimate the power output of the brightest light we can look at and the area of our pupil. Because we can look directly at the Sun (at least for very short periods of time),*the maximum power density we can tolerate is...

9. Chapter 5 Energy and Work
(pp. 139-172)

Now let’s look at human energy sources.

How much energy can a human produce?

Is it really worth it?

The words “energy” or “energetic” are used loosely to describe many things, from performances to batteries and from toddlers to automobiles. In science, energy has a more restricted meaning, but it includes energy of position (potential energy), energy of motion (kinetic energy), thermal energy, chemical energy, gravitational energy, etc. In a previous chapter, we looked at energy and recycling. In this chapter, we will look at energy and motion.

There are several forms of potential energy, including gravitational and spring. Gravitational...

10. Chapter 6 Energy and Transportation
(pp. 173-222)

We use a lot of energy to move things around. We try to do this as efficiently as possible, and we worry about the relative merits of bicycles, high-speed trains, hybrid cars, electric cars, biodiesel, airplanes, solar panels, etc. Some people also worry about consuming local foods to reduce transport costs. In this chapter we will look at many of these options and try to determine the relative costs of each. Of course, we will only be able to put them into “Goldilocks” categories, but that will be good enough for most purposes.

We will look at the energy needed...

11. Chapter 7 Heavenly Bodies
(pp. 223-288)

Heavenly bodies attract each other.*They also move in circles, rotating on their axes and revolving around each other.In order to describe their interaction and motion, we need to introduce gravity, tides, and rotational motion. As a result, this chapter will be the most mathematical. Because rotational motion is complicated, it will be introduced at the end of the chapter.

We’ll consider two effects of gravity, force and potential energy, and then discuss tidal forces. When we are close to the surface of a planet, the gravitational force on us from the planet is approximately constant (Fgrav= mg,...

12. Chapter 8 Materials
(pp. 289-310)

All materials are held together by the forces between atoms. By understanding the scale of these forces and the distances between atoms, we can understand the macroscopic forces holding materials together.

The important numbers are the typical (and, I hope, familiar) atomic binding energy of 1.5 eV and the typical atomic size of 10−10m.

What is the maximum strength of a material? In other words, what is the maximum weight that a 1-cm cable or rope could possibly support?

ANSWER: When we pull on a rope, it stretches. The distance between its atoms increases, and the atoms pull back....

(pp. 311-340)

Radiation is all around us, yet it is mysterious and scary to many people. As one of my students said, “If it’s natural, how can it be bad for you?” In this chapter we will estimate some common, uncommon, and extremely uncommon radioactive phenomena.

First, we need to introduce some concepts. “Radiation” consists of high-speed, high-energy particles. They can cause damage when they interact in material (such as our bodies). There are many sources of radiation, both natural and man-made. “Radioactive materials” emit radiation. Nuclear reactors emit radiation. The Sun, supernovas, and other cosmic sources emit radiation that are called...

14. Appendix A Dealing with Large Numbers
(pp. 341-346)
15. Appendix B Pegs to Hang Things On
(pp. 347-350)
16. Bibliography
(pp. 351-354)
17. Index
(pp. 355-359)