PN SAFURAA BINTI MOHD BASIR

JABATAN MATEMATIK, SAINS DAN KOMPUTER

DBS1012ENGINEERING

SCIENCE

OVERVIEW Describe base quantities, derived quantities

and the International System of units.

Define scalar and vector quantities.

2. Interpret data of measurement

Apply techniques for measurement to ensure accurate data by using measurement equipments:

Describe inaccuracy and errors in measurement:

a. Ruler

b. Vernier Callipers

c. Micrometer Screw Gauge

Solve problems of unit conversion.

1.Understand physical quantities

PHYSICAL QUANTITES(Quantities that can be

measured)

BASE QUANTITY(Quantity that CANNOT BE

DERIVED from other physical

quantity)

DERIVED QUANTITY

(Quantities that ARE DERIVED from the

combination of several base quantities by multiplication and

division.

The International System of Units (abbreviated SI from systeme internationale , the

French version of the name) is a scientific method of

expressing the magnitudes or quantities of important natural

phenomena.

BASE QUANTITYBase quantities : Physical quantity that can not be derived from other physical quantities. Base

QuantityBase

Quantity Symbol

SI Unit Symbol

Length l Meter m

Mass m Kilogram kg

Time t Second s

Electric Current

I Ampere A

Temperature

T Kelvin K

Derived QuantityDerived quantities : quantities that are derived from the combination of several base quantities by multiplication or division.

DerivedQuantity

Definition SI Unit in terms of base

units

Alternative name for SI

unit

Area, A length x length m2

Volume, V length x length x length

m3

Density, mass / volume kg m-3

Velocity, v length / time m s-1

Acceleration, a

velocity / time m s-2

Force, F momentum / time kg m s-2 newton, N

Pressure, P force / area kg m-1 s-2 pascal, Pa @ N m-2

Work, W force x distance kg m2 s-2 joule, J

Power, P work / time kg m2 s-3 watt, W

SCALAR & VECTOR QUANTITIES

• Scalar quantities are physical quantities with magnitude only.

• Vector quantities are physical quantities with direction and magnitude.

• Some examples of scalar and vector quantities:Scalar Quantity Vector Quantity

Speed DisplacementDistance VelocityVolume Acceleration

Temperature Force Time Momentum

PREFIXESPrefixes are the preceding factor used to represent very small and very large physical quantities in SI units.

Example : Use the suitable prefixes to represent the

numbers below:

i) 2 500 000 watt

ii) 0.001 500 gram

Solutions:

1 m = _____mm

CONVERSION OF UNITS

Change the following quantities to the units shown.

• a) 10 km = ____________m• b) 20 kg = _____________ g• c) 30 cm = ____________ m • d) 1.2 hours = _________ seconds• e) 45 cm2 = ____________ m2

List of some basic unit conversion

Example: Complete the following unit conversion a) 12 kmh-1 = __________ ms-1 

b) 25 cm2 = __________m2

c) 31.8 g/cm3 = __________kg/m3

List of some basic unit conversion

CONVERSION OF UNITS

ERROR & types of errorError is the difference between the actual value of a quantity and the value obtained in measurement

2 main types of error:

1. Systematic Error2. Random Error

SYSTEMATIC ERRORS

Sources of Systematic errors:

Instruments• errors in scale (zero error)• errors in apparatus (damaged and is not in good condition)

Physical conditions of the surroundings• Temperature and atmospheric pressure

Physical limitations of the observer• reaction time varies from one person to another

Systematic error can be reduced by :

Conducting the experiment with care. Repeating the experiment by using different instruments.

Systematic errors are errors that produce a result that differs from the true value by a fixed amount and the measurement is always greater or less than the actual value.

RANDOM ERRORS Random errors are errors of measurements in which the measured quantities differ from the mean value with different magnitudes and directions.However this readings are closed to the real value.Random error can cause by:

personal errors such as human limitations of sight and touch. lack of sensitivity of the instrument: the instrument fail to respond to the small change. natural errors such as changes in temperature or wind, while the experiment is in progress. wrong technique of measurement (parallax error).Ways to reduce random errors Taking repeated measurements to obtain an average value. Maintaining good experimental technique (e.g. reading from a correct position)

How to reduce ERROR??

1. Conduct the experiment with care.

2. Repeat the experiment by using different instrument.

3. Taking repeated measurement to obtain average value.

4. Maintaining a good experimental technique.

5. ……6. …………

BEAM BALANCE

VERNIER CALLIPER

RULER

MICROMETER SCREW GAUGE

STOP WATCH

MEASURING

CYLINDER

EXAMPLE OF MEASUREMENT TOOLS

MEASUREMENT AND MEASURING DEVICES

What we are going to do today?

We are going to read and use the following instruments in measuring certain quantities:

Ruler Vernier Callipers Micrometer Screw Gauge

measure length

RULERRuler: A ruler is used to measure lengths from a few

cm up to 1 m. A meter rule has an accuracy of 0.1 cm (1 mm).

Precautions to be taken when using a ruler(a) Ensure that the object is in contact with the ruler to avoid inaccurate readings.

(b) Avoid parallax errors.

(c) Avoid zero and end errors. The ends of a ruler, which may be worn out, are a source of errors in measurement. Thus it is advisable to use the division mark `1' of the scale as the zero point when taking a measurement.

How to read from a ruler

Length of the block, l =3.2cm-1.0cm = 2.2 cm

Diagram below shows the correct technique to use the meter ruler:

RULER – technique

VERNIER CALLIPERS

Parts of Vernier Callipers

Vernier caliper is more accurate than a ruler, since it has the smaller scale of 0.1 mm. Measure lengths of less than 10 cm. Can be used to measure outer dimensions of objects (using the main jaws), inside dimensions (using the smaller jaws at the inside dimensions, and depths (using the stem). The accuracy is up to 0.1 mm (0.01 cm).

How to Use a Vernier Callipers? 1) To measure outer/inner dimensions of an object, the object is placed between the jaws, which are then moved together until they secure the object. 2) The screw clamp may then be tightened to ensure that the reading does not change while the scale is being read.3) Take the reading.

Correct technique to use the vernier calipers:VERNIER CALLIPERS - technique

1. Ambil bacaaan 0 , 0 berada antara 7.0mm dan 8.0mm

2. Ambil baca yang selari antara bacaaan main scale

dengan Vernier scale, 0.5mm

3. Bacaaan = 7.5mm

MICROMETER SCREW GAUGE A micrometer screw gauge is more accurate than a ruler and vernier calliper because it has the smallest scale of 0.01 mm.The range of a micrometer is 0-25 mm.The accuracy of a micrometer is up to 0.01 mm.

How to Use a Micrometer?1) Turn the thimble until the object is gripped gently between the anvil and spindle.2) Turn the ratchet knob until a "click" sound is heard. This is to prevent exerting too much pressure on the object measured.3)Take the reading.

Parts of Micrometer Screw Gauge

MICROMETER SCREW GAUGE - technique

Determine the reading of the micrometer screw gauge below:

MICROMETER SCREW GAUGE - exercise