Day 1 – May 6 – WBL 1.1-1.2

Chapter 1Measurement and Problem Solving

Every branch of physics (and most other sciences) involves measurements and comparisons. In this chapter, we will introduce the SI units of measurement; base units, derived units, and prefixes. In particular, we will focus on the measurement of time, length, and mass.

PC141 Intersession 2013 Slide 1

Next, we will show how to convert measured values between different units, and explore the concept of significant figures.The chapter will conclude with a discussion of problem solving in physics.

Day 1 – May 6 – WBL 1.1-1.2

1.1 Why and How We MeasurePhysics attempts to describe nature in an objective way through measurement.

Measurements are expressed in units; officially accepted units are called standard units.

Major systems of standard units:• SI (Le Système international d’unités)

– a.k.a. the “metric system”– adopted nearly worldwide (since 1973 in Canada)

• Imperial or British units– Prevalent only in USA, Myanmar, and Liberia (but even then, not in the

sciences).– Used for some purposes in UK and occasionally in Canada. For the most part,

even the British don’t use them any more.– foot (ft), pound (lb), second (s)…technically “slug” instead of pound, for reasons

that will be clear in a couple of weeks.PC141 Intersession 2013 Slide 2

Day 1 – May 6 – WBL 1.1-1.2

1.1 Why and How We MeasureWhat are some examples of imperial units in use in Canada?

We also use a few non-metric (but non-imperial) units – particularly when measuring time (minutes, hours, days)

PC141 Intersession 2013 Slide 3

Day 1 – May 6 – WBL 1.1-1.2

1.2 SI Units of Length, Mass, and TimeThe SI system contains seven base units, which measure length, mass, time, electric current, temperature, amount of substance, and luminous intensity. These are called “base units” because none of them can be expressed as combinations of the others.

These seven units are believed to be all that are necessary to describe all phenomena in nature.

PC141 Intersession 2013 Slide 4

PC141 only requires units of length, mass, and time, referred to in this chapter as M, L, and T.

Electric current and temperature arise quite a bit in subsequent physics courses. The mole is constantly encountered in chemistry. The candela is rarely seen in undergraduate courses.

As base units, the metre, kilogram, and second are all defined in terms of a physical standard. The textbook contains a good description of the standards currently in use, on pp. 4-6.