by Bradley Knockel
In addition to being fascinating and directly useful in future classes and many professions (especially the professions in this modern economy), physics is useful in real life in at least three ways:
Physics may not help with personal relationships or acting professional, so it probably isn't even super important, but employees and voters having the ability to take and pass a physics course would be very advantageous for everyone. Physics classes are hard, so find the course that matches your current math ability, and be sure that you will have lots of time for studying! Physics may not be your or your children's strongest area, but it is important, and good grades should be encouraged.
Studies show that skills don't quickly transfer from one field to another. Just because you become good at physics, doesn't mean that you are necessarily good at anything else! We still have to learn whatever specific skills we need, though this can occur much more quickly if a similar skill is already mastered. The idea of learning physics is to have a great foundation for the technical or logical skills that we will need. Who can say exactly what skills we will need in 5 or 50 years. Let's build a strong foundation.
This one is sort of obvious and is far from being unique to physics. Keeping track of subscripts, minus signs, symbols, units, and significant figures throughout a physics calculation develops an ability to organize detail. I don't have to explain why this is important to anyone who works with computers, scheduling, strategy, cooking, money, filing systems, or any type of system (that is, anyone with a job). In the real world, a minor mistake often completely ruins the result, just like it does in physics. Physics students would have higher test grades if it weren't messing up details like units, not knowing the precise meaning of terms, or not rereading the question and checking their math.
For people newly learning physics, they often talk about gravity when they actually mean acceleration of gravity (g), the force of gravity (weight = w), constant of gravity (G), or even mass (m). Although mass is very related to gravity via w = m g, we can have mass without gravity, so it doesn't really even belong under gravity. Just thinking of all these things as gravity is ambiguous and will lead to all kinds of errors, and we must be more careful.
If you haven't learned about acceleration, forces, and weight yet, just ignore the following equations, but please read through the words to get the gist of it!
In chemistry, we could get away with not understanding the difference between mass and weight and just thinking of there being a conversion factor between kg (unit of m) and N (unit of weight), and we never need to worry about the acceleration of gravity or the constant of gravity. So 3.00 kg as a weight is...
3.00 kg (9.80 N / 1 kg) = 19.4 N
where the conversion factor
9.80 N = 1 kg
is what we would remember. To any physics person, this conversion factor is obviously untrue since N and kg are like apples and oranges (in fact, 1 N = 1 kg m/s2), but chemistry people are lucky and can get away with a certain sloppiness here because the force of gravity is basically the same everywhere on Earth's surface.
In physics, we want to think about any situation, not just a chemistry tabletop, so we need to understand the differences. What if an elevator on Earth is accelerating downward so that a scale on the floor pushes up on a person with a force of 60% their weight, and we want to know the acceleration (a) of the elevator? There is no conversion factor to do this since we don't know their weight or mass (asking the person is rude!), so we need the equation w = m g, which has the physics in it by carefully showing how quantities are related. We also need ΣF = m a, which is Newton's second law, since it can relate forces to acceleration (in the vertical direction)...
ΣF = m a
0.6 w - w = m a
-0.4 w = m a
-0.4 m g = m a
-0.4 g = a
a = -0.4 g
where g = 9.80 m/s2 since on Earth's surface, and a is negative since the elevator is falling. Note that we still don't know the weight or mass! It turns out that we can't know it from what's given, but we don't need to! In fact, we just solved the problem for all people in the elevator regardless of their mass, and I'll get back to this point in my third section.
If we follow this logical and careful way of thinking, we can get the correct answers. Common sense is very important in life and science, but common sense is often wrong, especially in science and math because we do not directly experience them on a daily basis (Google the Monty Hall problem for a good example!). Physics makes us learn how to think using logic, which guides our way when our common sense fails and teaches us the valuable lesson that many of the things we believe are wrong. Ideally, as we do physics more and more, it can even teach us how to expand our common sense to make it more correct! One of many important goals of getting an education is to not only show us that our common sense is often wrong, but to show us that we can improve upon it by trusting scientific fact. Common sense is only useful on small daily interactions. But, science allows us to go to outer space and technology allows us to form a global technological civilization and economy. For things vastly more complex than simple daily life, common sense fails, and we must become informed on scientific facts to make the best decisions. Sadly, many people still trust their common sense over proven fact when it comes to various political beliefs.
A real world analogy to carefully thinking about gravity is carefully using the word marriage. The word is very useful, but people often ambiguously use it when they shouldn't because they really mean wedding of marriage, the legal contract of marriage, the lifelong commitment of marriage, or even love. Just like mass had nothing and everything to do with gravity, love has nothing and everything to do with marriage. Love can happily exist without marriage.
The next time someone says "marriage is just a legal contract," they are wrong, but not necessarily for the reasons you might think. They are not necessarily saying that romantic relationships have nothing to do with love, but they could just be defining the ambiguous word marriage differently than you, which is not a real problem (although a few people think that love isn't important to romantic relationships). Often, the only problem with the statement is that they are using the word marriage too ambiguously—although maybe not if there is a certain context. If talking in a legal context, marriage means the contract. In a religious setting, marriage often refers to the commitment. It is important to understand these types of subtleties to prevent many of the useless arguments and conversations that occur.
With this careful way of thinking, we can actually answer some important questions. Should a person be able to marry a dog? Well, a dog cannot speak to participate in the wedding, cannot consent to a legal contract, and cannot express a lifelong commitment in a way that we could be certain (maybe a dog cannot even conceive of the future in a way that it could understand commitment). Should two people of the same sex be able to marry? Well, from a similar type of reasoning I just made, I don't see why not since people, unlike dogs, can fully participate, consent, and commit. No scientific/careful reasoning has shown any good reason for it not to happen. But notice that this careful way of thinking can miss some of the complexities: feelings of people. Gays want acceptance for who they are, which is a basic desire, so I hold their feelings above those who value forcing tradition on others (and far above the feelings of those who are insecure, think stereotypically, and maybe even are hateful). As a civilized society, we must protect those who are different and in the minority. After all, we are all in the minority in one way or another. Great ways to understand the feelings of people are diverse life experiences and film. Often, knowing an openly gay person is what helps us understand the issue on an emotional level. Other complexities to the issue of gay marriage are the legal arguments that need to be made to bring about the change that should occur, which involves being familiar with the legal system, the history of what types of legal arguments have been used to cause similar change, and how specifically the legal policy should be. Ignoring these legal issues regarding how to change things, scientific/careful reasoning has shown that people are born within a wide spectrum of brain type, hormonal makeup, sex chromosomes, and sexual organs, and there is evidence that what happens after we are born can determine our sexuality (though it's not a direct choice). The single scientific reason against gay marriage is that procreating is difficult, but all people have their personal challenges, so this really doesn't matter, especially considering that sterility—which is certainly worse than not being able to easily procreate—has never legally stopped marriages before and having members of society that do not have kids is likely good for the society. If this example of careful thinking inspires you to consider reinterpreting your religious text in the way that openly gay bishops do, that's good because a point of this example was to show that careful thinking is always difficult, always requires rethinking things, and is often painful in the short term.
Without knowing how to carefully think for ourselves, others who do not necessarily value the truth are most certainly thinking for us. Especially in this globally-connected technological world, careful thinking allows us as a representative democracy to choose our best path forward into the future.
Physics often oversimplifies complexities, so it is not the only thing required for thinking about complex things. Due to their very high complexity, the feelings of people cannot be understood analytically in any reasonable amount of time, but the type of analytical thinking that physics teaches can and must play a role in any decision involving laws, devices, or any other tool.
In the gravity example of the previous section, we found a general result, a = -0.4 g, that does not depend on mass or even the planet (the planet only determines the value of g). To do this, we had to use general formulas and use symbols like m for mass without ever having to know what number m stands for (in this case, m stands for any number!). Physics is about thinking generally and doesn't specialize like chemistry or other fields tend to do. We can solve a huge number of problems all at once and derive a general result and recognize when to apply that general result. For example, spinning a ball attached by a string to your hand and the Moon orbiting around the Earth can be understood to be the same phenomena described by very similar physics. The equations look exactly the same! Physics is about solving general problems and seeing how each specific situation differs from the previous situation by learning how to think in sophisticated and abstract ways. I saved this for last because it's the hardest!
In physics, we shouldn't memorize how to do a certain problem because we will never see the same problem twice. Many academic subjects that aren't physics trivially don't give us the same problem by changing numbers, but we still go through the same steps. In physics, it's all about understanding the relationships between things so that we can create our own steps. There are general problem-solving methods that we have to learn: organizing what we know in lists and pictures, being clear about what we want to know, recognizing relevant concepts, etc. These are just guidance and are not set in stone, and there are often (always?) many ways of doing a problem and getting the exact same correct answer.
I have heard people say that physics is solving word problems, which I agree with! This is why physics is so challenging and important. A situation with given quantities will be described in a physics (word) problem, and we then need to figure out some new thing that was not directly given in the problem. All word problems are different and require different combinations of equations for different reasons. We can understand physics and know how to think accurately and carefully, but word problems require something more advanced: being able to apply what we understand. It takes much effort and time to understand something well enough so that we can recognize when and how to use it. In physics, we have to understand things so well that we can make the many decisions about how to proceed when we are solving a problem.
General thinking is very useful in the real world that has real problems that have not yet been solved or have not been solved by the people we know. It's particularly useful for mathematical things, but it is also useful for planning a project or for not being that rigid employee who wastes people's time. In this modern real world, we need to know how to think if we want any real responsibility. If we learn how to do a specific task, that task will be done with different technology in a few years, and knowing how to think is how we can apply what we already know to the new environment and how to figure out which new things we should learn. If we are good at thinking, we can be the person who decides to change and manages the change to the new technology. In any type of problem solving, we need to be able to bring together the relevant things we know to start making progress on what we want to know. Physics teaches us how to think and adapt.
Real life obviously requires many skills that we keep learning along the way: communication skills, creativity, management, time management, initiative, being professional, emotional intelligence, having fun, etc. etc. But taking a physics class can help add an important piece to all of this. In fact, science itself requires many diverse skills and a strong imagination. All things are interconnected, so physics and life cannot be separated. Employers do look for people with the skills that physics can develop.
Physics isn't easy and takes lots of work, but maybe we now have a new motivation to work hard at it (in addition to curiosity and getting a diploma). In this busy world, I think that constructive motivation is at least as important as the actual doing. Physics will probably never be your favorite thing, but you can certainly gain from it by giving it your best effort, and I hope you will enjoy physics slightly more afterwards. Certain skills sometimes do not "click" until later in life after many attempts, so do not let science being presently difficult stop you!
Can you learn physics? Yes. Many people sadly think that they cannot. Science tells us that this attitude is, more often than not, a self-fulfilling prophecy that is passed within subcultures and within families. Any person's brain can do math! All people's brains benefit by doing mathematical things, just as music, socializing, and a diverse life help us all! If we listen to people who tell us we cannot, only then do we become someone who cannot. Not everyone should take the physics classes intended for technical majors, but that's another topic!
If you happen to strongly dislike physics even after many attempts at courses with various levels of math ability, I hope some science class interests you! Even the social sciences can provide many of the beneficial ways of thinking that I have described!
Hidden in all of this talk about why to learn physics are some clues on how to learn physics.
We have to be open to learning to think differently. It's not that we exactly have to change the way we think, but we have to try to add a new way of thinking. In the first physics class I took, this is what excited me and is what still excites me about physics. I can learn to see things in a new way that allows me to understand how they work. Being able to understand and describe the world is empowering and profoundly fascinating!
Seeing things in a new way takes lots of the right kind of thoughts! We should always try to connect what we learn to the real world we see every day and do it in a precise, careful, and general way. To see physics when we're driving, playing a musical instrument, cooking, playing sports, or anywhere, and trying to make sense of these daily things is really how we understand and enjoy physics, and we see that the ordinary world really is far from ordinary. Often, this just involves being mystified and trying to understand something, which is half the fun, and I think we need to try to understand in ten ways that are incorrect before we can actually understand the thing that is correct. I think we have to engage the ideas since just being told how things work isn't really the same.
But how specifically do we need to learn to think? Part of this is never letting ourselves not understand something before moving to the next thing, which is especially true in the beginning of a new topic such as classical mechanics or electromagnetism. Let's take classical mechanics as an example. We need to understand the first few chapters on kinematics, because that will provide the mathematical foundation on which everything in later chapters will be built. We must understand Newton's 3 laws because all of classical mechanics is based on them. We then must understand energy and momentum. Even when we "leave" classical mechanics to start learning electromagnetism, we will still need to understand all of these things I mentioned about classical mechanics, and we will be wasting some time if we try to learn the new thing without caring to still understand the old. Often, the best way to understand a thing is to move on to things based on it, but we need to make sure our understanding is as good as possible before moving on. A good level of understanding to aim for is the ability to do randomly chosen physics problems in a reasonable amount of time, which we learn to do by doing lots of physics problems! Try to predict things about the answer before you begin and then evaluate its meaning after you find it (try to understand why it is the correct answer). Clearing up points of confusion after every lecture is also very helpful! Try doing some problems slowly and neatly, then try doing some quickly, and just mix it up! As previously mentioned, focusing on why certain equations are used is better than trying to memorize how to do each problem. If we can know a small list of formulas that can be used to solve all problems and know how to use them by doing lots of examples, we are in a great situation!
There are many other tips for how to learn physics. An important one is to be involved by either participating in class or having conversations with classmates, tutors, and instructors. Another is to try to see math as a language that describes the world. For example, w = m g tells us that weight depends on mass and the gravitational acceleration at our location, which is an important way to see the difference between mass and weight. It can also be very useful to realize that we try to "trick" you in physics to make you question and fix your naive and usually incorrect assumptions, so think about things as we show you rather than either using your often incorrect common sense or just trying to learn the procedure instead of actually understanding things.