Professor Howard Brooks / How Things Work: Thinking Through Physics

A Few Words about Physics

Nature does what nature does. In Physics, we create models that allow us to predict what nature does.

When we’re trying to solve a problem, we ask whether the model we have in mind leads to a reasonable answer. If our model predicts that a mouse will run across a room at four kilometers an hour, or a cat will jump up fifty feet in the air, we need to rethink our model.

Physicists create a toolbox of models -- a handy kit of designs that help explain the physical world. We like to think of these models as spherical chickens.

What is a spherical chicken? you may ask.

If you are exploring, say, how objects move, you may imagine a chicken running across a road. But the feathers and beak and so forth are a distraction to your problem-solving, so you imagine your chicken to be a sphere, a little dot in space.

Getting Up to Speed in Physics I

Physics 120 begins with a study of motion in one dimension. Then we move to Newton’s Laws, enlarging the study of motion to two dimensions. After this, we put our minds to momentum and the conservation of energy.

To do well, the first step is to understand the problem you’re being asked to solve. Read the problem as a kind of story; then transform that story into visual images. Sketch the different parts of the problem; imagine it’s a movie unfolding in separate frames. Have fun with this.

Avoid distractors. Physics problems contain more information than you need. Sort through this information, putting aside numbers and circumstances that, while useful for other questions, are not useful in finding the answer to the question you have been asked to solve.

Equip yourself with a loose-leaf version of the textbook for Physics I, as it will make your learning and lab work more effective. As a bonus, you can use this book again in the next two semesters of Physics, if you decide to continue.
cont.
Read with a paper notebook open in front of you. When the text asks you to Stop and Think, do exactly that: stop and solve the problem in your notebook.

Read the assigned chapter more than once. New ideas will occur to you each time you read. Pay attention to what you didn’t notice the first time, but that you see clearly on re-reading.

Physics and Poetry

Physics, like poetry, asks us to think about the whole universe -- the vast, the tiny, the visible, the invisible.

Physicists, like poets, choose their words carefully.

Physics has its own language, and its key terms have very specific meanings. Often these meanings go back to the theory in which they first appeared. The word force, as used in Physics, comes from Sir Isaac Newton in the 17th century.

Over the centuries, a theory comes to read like a poem. Consider Newton’s Laws of Motion. Although we may explain these three Laws in various ways, they appear in our Physics textbooks today in the very words that Newton used when he explained them in 1687:

Every object persists in its state of rest or uniform motion -­ in a straight line unless it is compelled to change that state by forces impressed on it.

Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.

For every action, there is an equal and opposite reaction.

 You may find that these beautiful words ring a bell.