introduction physics

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CHAPTER 1INTRODUCTION TO PHYSICS

Understanding Base and Derived QuantitiesPhysical Quantity1. A physical quantity can be measured.2. A physical quantity is a property ascribed to phenomena, objects, or substances that

can be quantified.Examples :• angle of refraction—angle is the quantity and refraction is the phenomenon• area of rectangle—area is the quantity and rectangle is the object

• pressure of hydrogen gas—pressure is the quantity and hydrogen gas is thesubstance

3. To quantify a quantity is to measure that quantity and to give it a numerical value.Examples:(i) Length of a string = 2 500 centimeters = 2 500 cm

Here the quantity is the length, 2500 is its numerical value and cm is the unitused in the measurement.

(ii) Speed of a car = 90 kilometers per hour = 90 km h-1 The quantity here is the speed, 90 is the numerical value and km h -1 is the unit.

Scientific Notation and Unit Abbreviations

1 Scientific notation is used for large and small numbers. The general form of a number inthe scientific notation is A x 10n where A is a number between 1 to 10 and n is aninteger:

i) 2 500 cm is written as 2.5 x 103 cm and

ii) 0.0000 42 cm is written as 4.2 x 10-5 cm.2 Examples:

1. l000 m = 103 m = 1 km2. 2000000 m = 2 x 106 m = 2 Mm3. 3 000 000 000 m= 3 x 10

9 m =3 Gm

4. 0.001 m = 1 x 103 m= 1mm5. 0.000 001 m = 1 x 10-6 m = 1 µm

6. l 0000 s = l0 x l0

3

s= l0 ks7. 0.000 1 s = 0.1 x 10-3 s = 0.1 ms8. 3 x l05 Hz = 3 x l02 x l03 Hz = 3 x 102 kHz = 300 kHz


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Base and Derived QuantitiesBase Quantities:

Derived Quantities:Quantities which are derived from the base quantities.


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Example:From the formula for calculating velocity:

velocity =displacement

time=

lengthtime

as displacement is the base quantity length..’. The unit for velocity is m s-1.

Understanding Scalar and Vector Quantities

1. Distance always refers to how much ground an object has covered.2. Displacement refers to how far an object is from a reference point.3. The scalar quantity only has magnitude whereas the vector quantity has both

magnitude and direction.4. Properties of scalars and vectors

Worked Example 1.3A


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Fauziah travelled from Kuala Lumpur to Kangar, a distance of 507 km. After that, shecontinued her journey to Butterworth, a distance of 138 km. From Butterworth, Fauziahthen travelled back to Kuala Lumpur, a distance of 369 km. What is the total distancetravelled by Fauziah? What is the final displacement of Fauziah?

Solution

Total distance traveled = 507 + 138 + 369 = 1 014 km

Final displacement = 0 km

Adreen walked 3 m due east, and then 4 m due north. What is the total distancecovered by Adreen? What is the final displacement of Adreen?

SolutionTotal distance covered = 3 + 4 =7mFinal displacement = sUsing Pythagoras’ theorem,

s2 = 32 + 42 = 25.‘.s = √25 = 5 mtanθ = 4/3θ = 53.1º

Hence Adreen’s final displacement is 5 m from the starting point, 53.1 º north of east.

Precision and Accuracy

Precision (consistency) is the degree of uniformity or reproducibility of the measurements. Accuracy is the degree of closeness of the measurements to the true or accepted value.


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Figure (a) Azizah’s shots were precise and accurate because all 10 shots were consistentlyclose to each other.Figureb(b) Betty’s shots were precise but not accurate because all her 10 shots were far fromthe target but through her 10 shots were consistently close to each other.Figure (c) Devi’s shots were not precise and not accurate because all her 10 shots werespread far from the target and the spread of the shots was very wide.

Errors in MeasurementTable 1.4 Difference between random and systematic errors

Random Errors Systematic Errors

Random errors fluctuate from onemeasurement to the next. The readingsare distributed about a mean value thatis close to the true correct value.Random errors are due to:• Very small changes in the surrounding.• Outside disturbances which cannot be taken

into account.• Lack of sensitivity of the measuring

instrument:To reduce random errors:Take many readings of the same quantityand find the mean value.

The mean value will then be close to the trueor correct valueExample of random errors:Parallax errors — this is due to observernot reading the scale straight on.

Systematic errors tend to shift allmeasurements in a particular wayThe calculated mean value is displaced fromthe true or correct value.Systematic errors are due to:• Incorrect calibration of equipment.• Improper use of equipment.• Forgetting to account for some effects.To find out the systematic error in aninstruments.Use different instruments to measure thesame quantity.Comparing the data may reveal thesystematic error of a particular instrument.Example of systematic errors:Zero errors — the starting position of the pointer is not zero but some other value

..


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Figure 1.13 Zero error. Even though there is nothing on the weighing machine, the scalereading is not zero. The initial reading is +1 gram. So when using this machine to weigh anyobject, we need to deduct 1 gram from the reading to obtain an accurate result. This is anexample of a systematic error.

Understanding Scientific Investigations

The Scientific Method1. Identify the problems or questions.2. Identify the variables involved.3. Form a hypothesis connecting the variables and the question.4. Design and carry out experiments.5. Results: Collect the data and tabulate them.

6. Analyze the data.7. Interpret the data.8. Form a conclusion.

The quantity whose values we deliberately choose to change is called the manipulatedvariable. The quantity whose values depend on the manipulated variable is called theresponding variable. Those quantities whose values are kept constant throughout theexperiment are called fixed variables.

A hypothesis is a general statement of the relationship between a manipulated variable and aresponding variable in order to explain an event or observation.Manipulated variables are also known as independent variables.

A responding variable is also known as dependent variable.

NOTE-Suggestion time (30 minutes)


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Short Note• A physical quantity can be measured or calculated• Base quantities—mass, length, time,temperature, electric current.• Derived quantities—quantities derived from the base quantities.• Scalar quantities only have magnitude.• Vector quantities have both magnitude and direction.• The sensitivity of a measuring instrument is the capability of that instrument to

respond to physical stimuli or to register small physical amounts or differences inthe physical property measured.

• Any uncertainty in a measurement shows the limitations of the measuringinstrument and itself is not a mistake in the reading of the instrument.• When we take measurements errors are the mistakes we make in reading the

scales. Errors limit the accuracy of the measurement.• Precision (or consistency) is defined as the degree of uniformity or reproducibility

of the measurements.• Accuracy is defined as the degree of closeness of the measurements to the true

or accepted value.• Random errors fluctuate from one measurement to the next. The readings are

distributed about a mean value that is close to the true or correct value.• Systematic errors tend to shift all measurements in a particular way. The

calculated mean value is displaced from the true or correct value. Systematicerrors are due to incorrect calibration of the measuring instruments, or incorrectuse of the measuring instruments.

• A manipulated variable (independent variable) is the quantity whose values wedeliberately choose to change in an experiment.

• A responding variable (dependent variable) is the quantity whose values dependon the manipulated variable in the experiment.

• Fixed variables (constants) are quantities whose values are kept constantthroughout the experiment.

• A hypothesis is a general statement of the relationship between manipulatedvariables and a responding variable in order to explain an event or observation.


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AssessmentsObjective Questions1 Which of the following quantities is

not a derived quantity?

A Electric currentB Electric changesC Velocity

2 The following are scalar quantitiesexcept

A density B pressureC power D temperatureE acceleration

3 Which of the following unitconversions is true?

A 300 mm3 = 3.0x10-2 m3 B 650 mm3 = 6.5 x 10-6 m3 C 970 mm3 = 9.7 x 10-7 m3 D 2000 mm3 = 2.0x10-4 m3

4.

The figure above shows the readingof a micrometer screw gaugeobtained by a student frommeasuring 15 sheets of papers.

What is the thickness of one sheet ofpaper?

A 0.215 mm B 0.218 mmC 3.23 mm D 3.28 mm

5

The reading of the vernier calipersshown above is

A 0.15 cm B 0.18 cmC 0.28 cm D 0.51 cm


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Structure Questions

A. 1 Express each of the following in terms of its base S.I. unit.

(a) 1 km: __________________________________________________

(b) 5 ns: __________________________________________________

(c) 7 MV: __________________________________________________

(d) Choose the longest measurement from the following.

Answer: _______________________________________________________________

2 A wooden block measures 5.0 cm x 3.2 cm x 1.5 cm. The volume of the wooden blockis _______.

3 A mass of 45 µg is equivalent to ____________________ g.

B. 1 Find the derived units for each of the following physical quantities.

(a) Acceleration: ______________________________________________

(b) Speed: __________________________________________________

(c) Density: _________________________________________________

(d) Momentum: ______________________________________________

2 Which of the following quantities is not a derived quantity?

Answer: ________________________________________________________


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Essay question.

Swinger

Steel

1. Mister Potato is looking to a pendulum clock at one of the corner of his house. He findthat the speed of the pendulum increases when he shorten the steel that connect thebob and the swinger

Based on this observation:

a) State one inference that can be made. [1 mark]

b) Construct one suitable hypothesis for an investigation. [1 mark]

c) Using suitable material and apparatus, write one experiment report to test yourhypothesis. In your report, state:

i) Aim of experiment [1 mark]

ii) Experimental variables [2 marks]

iii) List of material and apparatus [1 mark]

iv) Arrangement of the apparatus [1 mark]

v) Experiment procedure including how to control the manipulated variable, how tomeasure the responding variable and repeat of the experiment [3 marks]

vi) Tabulation of the data [1 mark]

vii) Data analyse [1 mark]

Bob

introduction physics

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