Unit 1: About Science

eText Material

The eText for this course is a digital textbook that you can access through the link in the Course Orientation or on the course home page.

Throughout this Study Guide, unless otherwise indicated, all references are to the course eText, Conceptual Physics, 13th edition, by Paul G. Hewitt (Pearson, 2021).

Supplementary learning resources are available on Pearson’s Mastering Physics learning platform. Refer to the Course Orientation for instructions to access the site.

Additional Reading

Physics and Measurement

It’s sometime back in the mid-1980s. You’re driving home, listening to the hockey game on the car radio. You hear the excited voice of the commentator—he’s almost screaming—“Gretzky is waiting at the blue line; Kurri is at the corner digging out the puck! Kurri passes the puck. Gretzky is moving away from the blue line; now he has the puck. Gretzky is moving, faster and faster! He makes a beautiful move and splits the defence. He shoots. He SCOOORES!!!”

If you were a hockey fan in the ’80s, you were happy, but not surprised. You expected such wonderful plays from Wayne Gretzky, possibly the greatest hockey player of all time, one whose moves were described by ecstatic sportswriters as poetry in motion. What may surprise you is that those few lines of the commentator describing Gretzky’s goal can be used as starting points for several topics in this course.

Consider the following statement: “Gretzky is waiting at the blue line.” For the split second Gretzky is waiting, he is in a state similar to that of a book on a tabletop or a hot-air balloon suspended in the air—a body at rest, in the language of a physicist. As Gretzky moves faster and faster, a physicist observes an accelerating object, like an airplane during takeoff. And when Gretzky shoots the puck, the physicist thinks of elastic and inelastic collisions, conservation of energy and momentum, the forces of friction, and so on.

Physics, contrary to popular belief, does not only deal with things that are out of this world; the physical world we live in is also the subject matter of physics. This world is governed by laws that apply to everything happening within its boundaries, be it Gretzky’s breakaway goal or one air molecule colliding with another. Some of these laws we already know; others are yet to be found. Our purpose in studying physics is to learn the known laws, how they were discovered, and how they explain our observations of what is happening around us. With that knowledge behind us, we can attempt to discover those laws that are as yet unknown.

Units and Dimensions

Christine: “How much coffee do you drink, Mary?”
Mary: “About four.”
Christine: “Four what?”

In this conversation, Mary’s answer is incomplete because she gives a quantitative value without specifying the units. There is a big difference between four extra-large cups per day and four small cups per week!

Similarly, you won’t make much sense if you tell a person the distance between two points, A and B, is 100. The person will demand to know if you mean 100 kilometers, 100 feet, or maybe 100 angstroms! Physical quantities are expressed in numbers, but numbers are meaningless until you make it clear what unit of measurement is being used. Furthermore, a physical quantity changes depending on the choice of unit. For example, if you mean the distance between A and B is 100 miles, a person using kilometers as the unit of measurement will say the distance is 161 kilometers. The number 100 changes to 161 because a different unit of measurement is chosen.

Physicists consider themselves fortunate because all measurable physical quantities can be expressed using the units of length, mass, time, and electric current (or, alternatively, electric charge). These four fundamental units can be combined in various ways to express other units of measurement. The unit of velocity, for example, is expressed in terms of the units of length and time as follows: \begin{equation} \text{Unit of velocity} = \frac{\text{unit of length}}{\text{unit of time}} \end{equation}

At one time, there were many different sets of units, just as there are still different currencies in different countries. The English favored the foot–pound–second system (FPS system, also called the British Imperial System), in which length was measured in feet, mass was measured in terms of weight expressed in pounds, and time was measured in seconds. The rest of Europe at that time worked in the centimeter–gram–second system (cgs system) for the units of length, mass, and time. Now, the scientific world has agreed to use one set of units, called the International System of Units (or SI units, from the French Système international d’unités), in which length is measured in meters, mass is measured in kilograms, time is measured in seconds, and electric current is measured in amperes.

SI units are used in PHYS 210. However, keep in mind that there is nothing absolute about this system of measurement; it was chosen for standardization and convenience. One system of units can always be changed to another, the same way you can change dollars to euros and yen to pounds.

(Note: Although the animated videos in this course were originally created for PHYS 204, they cover the concepts presented in PHYS 210 and will enhance your learning.)

Questions

The following questions are selected from the end of Chapter 1 of the eText. It is important to your learning that you try to answer each question independently before you read through the answer and explanation given.

Additional Question

Answer the following additional question (not found in your eText).

Exercises

Spend some time completing the following exercises to test your understanding of the main concepts in Chapter 1 and increase your efficiency in answering exam questions.