1. Chapter 1
The Nature Of Science
Section 1.2 – Methods of Scientists

2. 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.

3. International Units System
To 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:
Kilograms – kg Kilometers - km
Meter – m
Second – s

4. Measurement We will learn of 6 different SI units as follow: Length
Weight and Mass
Area and Volume
Density
Time
Temperature

5. 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).

6. 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.

7. 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).

8. 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.

9. 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.

10. 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).

11. 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).

12. Time
Time is the interval between two events and usually measured with a watch or clock.
The SI unit of time is second (s).

13. 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.

14. 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.

15. 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.

16. Try these What is the SI unit for the following quantities: Mass
Temperature
Weight
Length
Area
Volume
Time
Density
Mass -
Temperature - Kelvin
Weight- Newton
Length
Area – square meters or square centimeters
Volume – Cubic meter or cubic centimeters
Time – seconds
Density

17. Try these What is the scientific notation for the following:
m/s (the speed of light)
kg (the mass of an electron)