Chapter #1 Ms. Hanan Anabusi The Science of Physics Chapter #1 Ms. Hanan Anabusi

1-2 Measurements in Experiments Objectives List basic SI units and the quantities they describe. Convert measurements into scientific notation. Distinguish between accuracy and precision. Use significant figures in measurements and calculations.

Numbers as Measurements Numerical measurements are required in Physics. Numerical measurements are different from the numbers used in a mathematics class. In science, numbers has dimension. Dimension is the description of what kind of physical quantity is represented by a certain measurement . The basic dimensions are length, mass, and time

SI Standards SI (System International) is the standard measurement system for science. In 1960, an international committee agreed on the SI measurement system. The base SI units of length, mass, and time are the meter (m), kilogram (kg), and second (s). Units can be combined to form derived units (m/s, m/s2, etc..) SI uses prefixes to accommodate extremes. See table 1.3 on page 12. Build conversion factors to convert a measurement from its prefix form (32.7 mm to meters). Both dimension and units must agree.

Prefixes Ladder

Sample Problem A typical bacterium has a mass of about 2.0 fg (femto gram). Express this measurement in terms of grams and kilograms.

Solution Given: mass = 2.0 fg Unknown: mass = ? g mass = ? kg Build conversion factors from the relationships given in Table 1-3. Two possibilities are shown below. Only the first one will cancel the units of fg to give units of g. Then take this answer and use a similar process to cancel the units of g to give units of kg.

Classroom Practice 1- The mass of an average woman is 60000000 mg. express this in grams and kilograms 2- The mass of a proton is . Express this in g, mg, and kg

Even questions (2 and 4) as class-work, and Practice A Page 15 Questions 1, 2, 3, 4, and 5 Even questions (2 and 4) as class-work, and odd questions (1, 3, and 5) as homework