Chapter 1 Measurements, Units and Problem Solving College Physics Chapter 1 Measurements, Units and Problem Solving

Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. Why and how we measure ?

All quantities are some number of standard units All quantities are some number of standard units. Always the combination of number and unit. “this lecture is about 4 hours long” The earth’s radius is about 6,356.750 km Standard Units

Standard Units These are examples of standard units: L = meters (m) M = kilograms (kg), T = seconds (s) Standard Units

A group of standard units and its combinations is called : System of Units System of Units

The International System of Units, universally abbreviated SI (from the French Le Système International d'Unités), is the modern metric system of measurement. System of Units SI

System of Units SI the meter for distance, the kilogram for mass, the second for time, System of Units SI

the SI base unit of distance Length

The SI mass standard: the kilogram (kg) (a) The kilogram was originally defined in terms of a specific volume of water, that of a cube 0.10 m on a side, thereby associating the mass standard with the length standard. The standard kilogram is now defined by a metal cylinder. (b) The international prototype of the kilogram is kept at the French Bureau of Weights and Measures. It was manufactured in the 1880s of an alloy of 90% platinum and 10% iridium. The SI mass standard: the kilogram (kg)

The SI time standard: the second The second was once defined in terms of the average solar day. (a) It is now defined by the frequency of the radiation associated with an atomic transition. (b) The atomic fountain "clock" shown here, at NIST, is the time standard for the United States. The variation of this "timepiece" is less than one second per 20 million years. The SI time standard: the second

Prefixes The metric system uses prefixes to describe powers of 10, 1kilometer = 1km = 1000m = 10^3 meters. Prefixes

Significant figures Significant figures are the number of important digits in a measurement. If a textbook’s length is 0.2742m = 27.42cm = 274.2mm, one can see that there are 4 significant digits. To help us determine the number of significant figures, there are some simple rules: zeros at the beginning of a number are not significant, they merely locate the decimal point: 0.0254m → 3 sig. figs. zeros in the middle of a number are significant: 104.6m → 4 sig. figs. 3. zeros at the end of a number after a decimal point are significant: 215.00m → 5 sig. figs.

Units in calculation

General procedure for solving problems in physics