2. Physics (cont. 2)Physics (cont. 2)
QUANTITIES AND UNITSQUANTITIES AND UNITS
Length of the table = 2 meter
Speed of the car = 75 meter/second
Mass of stone = 5 kg
Fundamental quantity
QUANTITY
Derived quantity
Fundamental quantities: length, mass, time, temperature, electric current,
luminous intensity, amount of substance
Derived quantities: speed, area, volume, etc. (See p. 3 – deriving the
quantities)
3. Physics (cont. 3)Physics (cont. 3)
UNITSUNITS
Every measured quantity comprises of aEvery measured quantity comprises of a
number and a unit. For example, timenumber and a unit. For example, time
elapsed = 15 minutes.elapsed = 15 minutes.
Time = quantityTime = quantity
1515 = number= number
minutes = unitminutes = unit
Fundamental unit
UNIT
Derived unit
NoNo QuantityQuantity SymbolSymbol UnitUnit
11 LengthLength ll meter (m)meter (m)
22 MassMass mm kilogram (kg)kilogram (kg)
33 TimeTime tt second (s)second (s)
44 TemperatureTemperature TT kelvin (K)kelvin (K)
55 Electric currentElectric current ii ampere (A)ampere (A)
66 Luminous intensityLuminous intensity II candela (cd)candela (cd)
77 Amount ofAmount of
substancesubstance
NN molemole
(mol)(mol)
4. Physics (cont. 4)Physics (cont. 4)
MEASUREMENTMEASUREMENT
We need standard and stable methods of measurement to communicateWe need standard and stable methods of measurement to communicate
scientific work.scientific work.
Measuring the length of an object
Apparatus: ?
How: ?
5. LengthLength
In our daily life, length is used forIn our daily life, length is used for
measuring distance, thickness of anmeasuring distance, thickness of an
object, etc. In science, lengthobject, etc. In science, length
represents the distance between tworepresents the distance between two
points, for instance the length of thepoints, for instance the length of the
side of a triangle is the distanceside of a triangle is the distance
between two corners of the triangle.between two corners of the triangle.
Length uses SI unit in meter (m). OneLength uses SI unit in meter (m). One
standard meter is the same as thestandard meter is the same as the
distance traveled by the light in adistance traveled by the light in a
vacuum in 1/299792458 second. Forvacuum in 1/299792458 second. For
our life, measuring tools have referredour life, measuring tools have referred
to a standard meter, such as ruler,to a standard meter, such as ruler,
vernier caliper, and meter tape. Thevernier caliper, and meter tape. The
smallest measurement unit for a metersmallest measurement unit for a meter
tape and ruler is 1 milimeter, while fortape and ruler is 1 milimeter, while for
a vernier caliper it is 0.1 mm.a vernier caliper it is 0.1 mm.
Length can also be stated in smaller unitLength can also be stated in smaller unit
than a meter by adding prefixes asthan a meter by adding prefixes as
shown in the following table.shown in the following table.
The SI is easy to use because it uses theThe SI is easy to use because it uses the
10 multiplying factor as seen in the10 multiplying factor as seen in the
table. The prefixes before the basictable. The prefixes before the basic
unit of SI show 10 with certain figureunit of SI show 10 with certain figure
as the chosen exponent. For example,as the chosen exponent. For example,
kilo uses figure 3 as the exponent orkilo uses figure 3 as the exponent or
1000 = 10?. One (1) kilometer is 1,0001000 = 10?. One (1) kilometer is 1,000
meters.meters.
PrefixPrefix SymbolSymbol Multiplying factorMultiplying factor
kilokilo kk 1000 = 10?1000 = 10?
hectohecto hh 100 = …100 = …
decadeca dada 10 = …10 = …
decideci dd 0.1 = …0.1 = …
centicenti cc 0.01 = …0.01 = …
milimili mm 0.001 = …0.001 = …
micromicro μμ 0.000001= …0.000001= …
nanonano nn 0.000000001=…0.000000001=…
6. If the length of an object is in meter, how can we state it in centimeter? WeIf the length of an object is in meter, how can we state it in centimeter? We
know that 1 m = 100 cm. One hundred shows the comparison betweenknow that 1 m = 100 cm. One hundred shows the comparison between
meter and centimeter, called ratio. To convert meter to centimeter, multiplymeter and centimeter, called ratio. To convert meter to centimeter, multiply
meter with the ratio and to convert the centimeter to meter, just divide it bymeter with the ratio and to convert the centimeter to meter, just divide it by
the ratio.the ratio.
Example:Example:
3m = 3 x 100 cm = 300 cm3m = 3 x 100 cm = 300 cm
20 cm = 20 / 100 m = 0.2 m20 cm = 20 / 100 m = 0.2 m
Thus, to convert the units you have to: 1) find the ratio between the two units, 2)Thus, to convert the units you have to: 1) find the ratio between the two units, 2)
convert them from the large unit to the small one, just multiply them with theconvert them from the large unit to the small one, just multiply them with the
ratio, while from the small unit to the larger one, divide them by the ratio.ratio, while from the small unit to the larger one, divide them by the ratio.
Exercise:
1. The length of a table is 2 meters. What is the length of the table in millimeter?
2. The width of a book is 15 centimeters. What is the width of the book in
decimeter and meter?
3. The distance between two houses is 5 kilometers. State this distance in meter.
7. Vernier CaliperVernier Caliper
This apparatus can be used for measuring: 1) the outside diameter or width ofThis apparatus can be used for measuring: 1) the outside diameter or width of
an object, 2) the inside diameter or width of an object, and 3) the depth ofan object, 2) the inside diameter or width of an object, and 3) the depth of
an object.an object.
Reading a vernier caliperReading a vernier caliper
1.1. Read the centimeter mark on the fixed scale to the left of the 0 – mark onRead the centimeter mark on the fixed scale to the left of the 0 – mark on
the vernier scale.the vernier scale.
2.2. Find the millimeter mark on the fixed scale that is just to the left of the 0 –Find the millimeter mark on the fixed scale that is just to the left of the 0 –
mark on the vernier scale.mark on the vernier scale.
3.3. Look along the ten marks on the vernier scale and the millimeter marksLook along the ten marks on the vernier scale and the millimeter marks
on the adjacent fixed scale, until you find the two that most nearly line up.on the adjacent fixed scale, until you find the two that most nearly line up.
4.4. To get the correct reading, simply add this found digit to your previousTo get the correct reading, simply add this found digit to your previous
readingreading
Parts of a vernler caliperParts of a vernler caliper
1.1. Outside jaws: used to measure external lengthsOutside jaws: used to measure external lengths
2.2. Inside jaws: used to measure internal lengthsInside jaws: used to measure internal lengths
3.3. Depth probe: used to measure depthsDepth probe: used to measure depths
4.4. Main scale (cm)Main scale (cm)
5.5. Main scale (inch)Main scale (inch)
6.6. Vernier (cm & inch)Vernier (cm & inch)
7.7. Retainer: used to block movable part to allow the easy transferring aRetainer: used to block movable part to allow the easy transferring a
measurementmeasurement
