CHAPTER 1

The Nature Of Science

Section 1.2 – Methods of Scientists

LE SYSTEME INTERNATIONAL

D’UNITES - SI

This system is a modern version of the metric system.

SI is based on a decimal system that uses the number 10 as the base unit.

INTERNATIONAL UNITS SYSTEMTo critically evaluate the merit and validity of

scientific research and experiments, it is essential that scientists communicate using the same system of measurements.

Most scientists used SI.

The basic units in this system are:1. Kilograms – kg Kilometers - km2. Meter – m3. Second – s

Measurement We will learn of 6 different SI units as

follow:1. Length2. Weight and Mass3. Area and Volume4. Density5. Time6. Temperature

Length The SI unit to measure length is the meter

(m). 100 cm = 1 m 10 mm = 1 cm 1000 m = 1 km

Long distance is measured in kilometers (km).

Weight and Mass Weight is a measure of the gravitational

force on an object. Weight is typically measured with some

type of scale. Unlike mass, weight varies with location. The weight of the astronaut on the moon

is about one-sixth the astronaut weight on Earth.

Weight and Mass

This is because the gravitational force exerted by earth on the astronaut is one-sixth the force exerted by Earth on the astronaut.

Weight is a Force and the SI unit is Newton (N).

The SI unit for mass is kilogram (kg).

Weight and Mass Mass is the amount of matter in an object

and depends on number and kinds of atoms that make up the object.

The mass of an object, unlike weight does not change with an object’s position.

Area and Volume Area requires a combination of SI units. Area is the amount of surface included

within a set of boundaries and is expressed in square units of length, such as square meter (m²) or square centimeters (cm²).

Area = length x width.

Volume is the amount of space occupied by an object.

Area and Volume

The SI units of volume for regularly shape, solid object is the cubic meter (m³) or cubic centimeter (cm³)

The SI units of volume for liquid are usually made in milliliters (mL), or liter (L).

Density Density is a measure of the amount of matter

that occupies a given space.

Density = mass / volume.

Density SI units is often expressed in grams per cubic centimeter (g/cm³), or grams per milliliters (g/mL), or kilograms per cubic meters (kg/m³).

Time

Time is the interval between two events and usually measured with a watch or clock.

The SI unit of time is second (s).

Temperature Temperature is a measure of the average

vibrations of the particles that make up a material.

A mass made up of particles that vibrate quickly has a higher temperature than mass whose particles vibrate more slowly.

Temperature is measured in degrees with a thermometer.

Temperature In science usually the temperature units is

Celsius (C).

The SI units of temperature is Kelvin (K).

The coldest possible temperature is absolute zero, or 0º K, which is equal to -273ºC.

Scientific Notation In a scientific notation, a number is expressed as a

value between 1 and 10 multiplied by a power of 10.

The power of 10 is the number of places the decimal point must be shifted so that only a single digit remains either to the left or right of the decimal point.

If the decimal point is shifted to the left the exponent of 10 is positive.

If the decimal point is shifted to the right the exponent of 10 is negative.

TRY THESE What is the SI unit for the following

quantities: Mass Temperature Weight Length Area Volume Time Density

TRY THESEWhat is the scientific notation for the following:299 792 490 m/s (the speed of light)

0.000 000 000 000 000 000 000 000 000 000 911kg (the mass of an electron)