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Measurements and Calculations • Measurement is an integral part of physics like any other scientific subject. • Definition measurement: defined as comparison of an unknown quantity with some known quantity of the same kind Dr/Amira A tef.

Measurements and Calculations • Measurement of an object consists of: 1- the unite of measurement 2- the number of units the object measures Dr/Amira A tef.

Measurements and Calculations • Measurements Each measurement is associated with a physical quantity • Characteristics of standards for measurements • Readily accessible • Possess some property that can be measured reliably • Must yield the same results when used by anyone anywhere • Cannot change with time Dr/Amira A tef.

• There are two type of observations 1- Quantitative observations: involve measurements or estimates that yield meaningful, numerical results. 2-Qualitative observations: yield descriptive, non numerical results. Although all the observations we can make on a phenomenon are a valuable, quantitate observations Dr/Amira A tef.

• Pick out quantitate and qualitative observations from each phrase. 1- 3.0 grams of Nacl dissolve in 10 militers of H2o to produce a clear solution. Dr/Amira A tef.

Solutions Quantitative: 3.0 grams and 10 militers Qualitative: clear solution.

• 2- the spider on the wall has only seven legs remaining but is still big and hairy Dr/Amira A tef.

Solutions Quantitative: 3.0 grams and 10 militers Qualitative: clear solution.

Fundamental and derived SI units • The fundamental units are the base units defined by intentional system of units. These units are not derived from any other unite, therefore they are called fundamental units. • The seven base units are 1- Meter (m) for length 2- Second (s) for time 3- Kilogram (kg) for weight 4- Ampere (A) for electricity 5- Kelvin (k) for temperature 6-Mol (mol) for amount of substance 7- Candela (cd) for luminous intensity Dr/Amira A tef.

• Derived unite are units of measurements derived from the seven base unite specified by the international system of unite (SI) they are • Speed - measured in meters per second (m s-1). Acceleration - measured in meters per second per second (m s-2). • density - measured in kilograms per meter3 (kg m3). Dr/Amira A tef.

System of measurement • System of measurement is collection of units of measurement and rules relating their to each other. • SI system is a special set of metric units Dr/Amira A tef.

International System (SI) base units: Mass(m) Kilogram Kg Length(L) meter M Time(t) second S Temperature(T) Kelvin K Electric Current intensity (I) Ampere A Luminous Intensity Candela C Amount of substance mole D mole.

o All of the other SI units are derived from these base units base unit of length: meter(m) 1 kilometer(km) = 1000meter{m) 1 centimeter(cm) = 0.01 meter{m) 1 nanometer (nm) = 1 109meter{m) base unit of mass: gram {g) 1 kilogram {kg) = 1000 gram (g) 1 milligram {mg) = 0.001 gram {g) base unit of volume: liter (L) base unit of time: second {s) 1 milliliter (mL) = 0.001 liter{L) 60 seconds{SJR1 minute {min) 1000milliliter(mL) = 1 liter (L) 60 minutesfmin) = 1 hour{h) Prefix (symbol) Value giga {G) 109 mega (M) 106 kilo (k) 103 deci (d) 10' cent! (c) 10 = milli On) 10 3 micro (|j) 10^ nano {n) 109 1 mL = 1 cc = 1cm3.

Volume = length x width x height = m x m x m Density = mass / volume = kg / m3 Speed = distance/ time Acceleration = velocity/ time Force = mass x acceleration newton (N) Pressure = force / Area pasjcal (Pa) Work = Force x Displacement joule (J) Power = work done / time watt (W) = m3.

Prefix Abbreviation Power nano n −9 10 micro m −6 10 milli m −3 10 centi c −2 10 deci d −1 10 kilo k 3 10 mega M 6 10 giga G 9 10.

Scalar quantities:-Scalar quantities are quantities that have magnitude only. Two examples are shown below:.

Vector quantities:- Vector quantities are quantities that have both magnitude and direction Dr/Amira A tef.

Scalars Vectors distance displacement speed Velocity mass weight time acceleration pressure force energy momentum volume density Dr/Amira A tef.

r j Uncertainty and error in measurement Some error is inevitable even with high precision instruments Two main types of errors • Random errors • Systematic errors.

Systematic error Random error •Is the one that remains constant or changes in regular fashion in repeated •is repeatable error associated with equipment or a flawed experiment design •Random errors in experimental measurements are caused by unknown and unpredictable changes in the experiment these changes may occur in the measuring instruments or in the environmental conditions. •Random error →has no pattern one minute your readings might be too small. The next they might be too large. •Minimize by improving design of the apparatus Minimize by repeated taking the reading • Dr/Amira A tef.

1- Which one of the following is not a unit of length: Angstrom Micron Radian Light year 2- Which is not a base unit in SI units? Kilogram Joule Ampere Kelvin 3-An example of derived unit is Candela Ampere Coulomb Mole Dr/Amira A tef.

4-Candela is the SI unit of Charge Luminous intensity Power Refractive index 5- Which is a derived unit: Candela Ampere Kelvin Newton 6- The unit of force is and its symbol is which is the correct pair? length, n mass, N density, n newton, N Dr/Amira A tef.

10-The prefix pico is equal to a) 10–6 b) 10–12 c) 10–18 d) 10–11 11- The SI unit of intensity of light is: Mole Kelvin Candela Ampere 12- A light year is a unit for a) Time b)Distance c)Velocity d)Time period Dr/Amira A tef.

15- Error in measurement may occur due to a) Inexperience of a person b) The faulty apparatus c)In appropriate method d) Due to all reasons in a, b and c 16- Error is the one that remain constant or changes in regular fashion in repeated a) Systematic Error b) Random Error c) Personal Error d)None Dr/Amira A tef.