MEASUREMENT

• We obtain an understanding of our environment by observing the physical world through measurements.

• Measurement is a comparison of physical quantity with a standard unit.

MEASUREMENT• It is expressed with numbers and units.

• Physical characteristics can be expressed in terms of fundamental quantities.

• Our comprehension of the physical world is based on fundamental quantities.

FUNDAMENTAL QUANTITIES

Four quantities have been identified and specified as fundamental.

These are:• Length• Mass• Time• Electric charge

They form the basis for other quantities necessary to describe and understand the physical sciences.

Length

• We use length to measure location or size.

• Length is defined as the measurement of space in any direction.

Note: Space has three dimensions, each is measured by length.

• Consider a box:Length (l)Width (w)Height (h)

Time

• Time is the continuous forward flow of events.

• Events allow us to precise time, without events, we have no innate awareness of time.

Mass

• Mass quantifies matter.

• Mass refers to the amount of matter an object contains.

Electric Charge

• Electric Charge is the property associated with some particles, that gives rise to electric forces and electrical phenomena.

STANDARD UNITS

• A standard unit is a fixed and reproducible value for the purpose of taking accurate measurements.

• A set of standard units is referred to as a system of units.

British System

British System uses the familiar unit of:Length: foot Mass: Slug Weight: pound Time: SecondElectric Charge: Coulomb• Note: It is also called the Gravitational System

of Units.

Metric System

Metric System is considered to be simpler than the British System as the conversion is by a factor of ten.The standard units of:• Length – meter, m• Mass – kilogram, kg• Time – seconds, s• Electric Charge: Coulomb

They are called the International System of Units (SI units).

Systems of units

Metric System• Length – meter, m• Mass – kilogram, kg• Time – seconds, s• Electric Charge -

Coulomb

British System

Length: foot

Mass: Slug

Time: Second

Electric Charge: Coulomb

Weight: pound

International System of Units

There are seven base units of the International System of Units.• Meter, m, measures length.• Kilogram, kg, measures mass.• Second, s, measures time.• Ampere, A, measures electric current.• Kelvin, K, measures temperature.• Mole, mol, measures amount of substance.• Candela, cd, measures luminous intensity.

Derived Quantities

• Derived Quantities are formed by combining two or more of the fundamental quantities.

Examples:• Area = length x width• Volume = length x width x height• Speed = distance/time• Density = mass/volume

Density

Density refers to how compact or crowded a

substance is, that is, the amount of mass

located in a definite volume.

Density is simply the mass per unit volume.

Density = mass/volume

Measurement Errors

Systematic Errors:

• Systematic errors are associated with instruments or the technique used.

They are as a result of:

• Improperly calibrated instrument

• Error incurred from observer’s reading

Measurement Errors

Random Errors:

• Random Errors result from unknown and unpredictable variations in experimental situations.

• Such as fluctuation in electrical voltage.

• Changes in temperature, pressure, etc

Accuracy / Precision

• Accuracy indicates how close measurement comes to the true value.

• Precision refers to the agreement among repeated measurement, that is, how close they are together.

Converting Quantities

1. Use a conversion factor, a ratio relating

one unit to another.

2. Choose the appropriate form of the conversion factor(s) so that the unwanted units cancel.

3. Check to see that the unit cancel and that

you obtain the desired unit.

Converting Quantities

Desired quantity and units = given

quantity and units x conversion factor

Common relationships

• 1 kg = 2.2 lbs.

• 1 lb. = 453.6 g

• 1 inch = 2.54 cm

• 1.06 qt = 1 L

• 1.0 mile = 1.609 km

Temperature

A measure of hotness or coldness of an

object .

Types of temperature scales:

• Fahrenheit: on this scale the normal freezing and boiling points of water are taken to be 32F and 212F respectively.

• Celsius: Boiling point is 100C and the freezing point is 0C

0ºC 32ºF

0ºC = 32ºF

100ºC 212ºF

100ºC = 212ºF

0ºC 32ºF

0ºC = 32ºF

Relationship Between oC and oF

There is no direct relationship between K

and oF. Therefore, one must go through oC

in order to get temperature in K.

oF = 1.8 oC + 32

K = oC + 273