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Scientific Method

SCIENTIFIC METHOD

The scientific method is a logical and rational order of steps by which scientists come to conclusions about the world around them. The scientific method helps to organize thoughts and procedures so that scientists can be confident in the answers they find. Scientists use observations, hypotheses and deductions to make these conclusions, just like you will use the scientific method in your science fair project. The steps of the scientific method are:

  • Observation/Research
  •    Hypothesis
  •    Prediction
  • Experimentation
  •   Conclusion

 

OBSERVATION

This step could also be called “research”. It is the first stage in understanding the problem you have chosen. For this stage of the scientific method, it is important to use as many sources as you can find. The more information you have; the better the design of your experiment is going to be.

HYPOTHESIS

The next stage of the scientific method is known as the “hypothesis”. This word basically means “a possible solution to a problem, based on knowledge and research”. The hypothesis is a simple statement that defines what you think the outcome of your experiment will be.

PREDICTION

The hypothesis is your general statement of how you think the scientific phenomenon in question works. Your prediction lets you get specific-how will you demonstrate that your hypothesis is true? The experiment that you will design is done to test the prediction. An important thing to remember during this stage of the scientific method is that once you develop a hypothesis and a prediction, you shouldn’t change it, even if the results of your experiment show that you were wrong. An incorrect prediction doesn’t mean that you “failed”. It just means that the experiment brought some new facts to light that maybe you hadn’t thought about before.

EXPERIMENTATION 

This is the part of the scientific method that tests your hypothesis. An experiment is a tool that you design to find out if your ideas about your topic are right or wrong. The experiment is the most important part of the scientific method.

CONCLUSION

The final step in the scientific method is the conclusion. This is a summary of the  experiment’s results, and how those results match up to your hypothesis.

There are two options for your conclusions: Based on your results, either you can reject the hypothesis, or you cannot reject the hypothesis. A hypothesis cannot be proved with a single experiment, because there is a chance that you made an error somewhere along the way. Hence, on the basis of results of many experiments, what you can say is that your results support the original hypothesis.

If your original hypothesis didn’t match up with the final results of your experiment, don’t change the hypothesis. Instead, try to explain what might have been wrong with your original hypothesis. What information did you not have originally that caused you to be wrong in your prediction?

What are the reasons that the hypothesis and experimental results didn’t match up? The flow sheet for the scientific method is shown in Fig. 2.19.

EVALUATE YOURSELF

I. Objective Type Questions

Select the most appropriate choice from the options given as (a), (b), (c) and (d) after each question:

1 Two students A and B report the mass of the same substance as 12.0 g and 12.00 g,  Respectively. Which of the following

(a) Both are equally accurate

(b) A is more accurate than B

(c) B is more accurate than A

(d) Both are scientifically inaccurate.

 

2. Which of the following is incorrect about SI units?

(a) Density in kg m-3              (b) Force in Newton’s

(c) Pressure in Pascals             (d) Amount of substance in mol L-1

 

3. Picometer (pm) and nanometer (nm) are correctly related as

(a) 1 pm = 10 nm                     (b) I nm = 10 pm

(c) 1 pm = 100 nm                   (d) 1 nm = 1000 pm.

 

4. kg m-1 s-2 is the unit of

(a) momentum                         (b) velocity

(c) pressure                              (d) acceleration.

 

5. The prefix atto (a) stands for

(a) w-9                                      (b)10-12

(c) I0-18                                    (d)10-15.

 

6. Acceleration is the increase in velocity of a body per unit time.

The correct unit for it is:

(a) N kg-1

(c) Jm-1

(b) m2 s-2

(d) kg m-3.

 

7 Which of the following is not an SI unit?

(a) kelvin         (b) metre          (c) ampere      (d) yard.

 

8. A sample of compound contains 20.45% of chlorine. The chemical analysis of the sample by two methods A and B gave a mean value of 20.60% and 20.54% respectively. The  percentage accuracy of

(a) A is less than B hence B is more accurate

(b) A is greater than B but B is more accurate

(c) A is less than B hence A is more accurate

(d) Both the results are accurate.

 

9. Which of the following reported values is more precise

(a) 20.45 ± 0.15           (b) 20.60 ± 0.05

(c) 20.20 ± 0.10           (d) 20.50 ± 0.02.

 

10. Four students A, B, C and D reported the percentage of Aluminum in the sample as

Student           Student          Student          Student

A                     B                    C                    D

20.50               20.75               20.20               20.20

20.48               20.65               20.25              20.40

20.52               20.40              20.15              20.00

20.50               20.28              20.20              20.60

On the basis of these results it can be concluded that

(a) A has good precision and good accuracy

(b) B has good precision but low accuracy

(c) C has good precision and good accuracy

(d) D has poor precision but good accuracy.

 

II. Fill in the Blanks

11 . Complete the following sentences by supplying appropriate words:

(i)                 A systematic error which makes all the measurements wrong by a certain amount is known as ………… .

(ii)               Two numbers are reported as 2.7182820135423 and 2.718281828. Among these numbers first is more ……….. . and second is more …………

(iii)             The mass of moon is reported as 7.3 x 1022 kg. In a calculation it is found to be 6.9 x 1022 kg, the accuracy of calculation is ………… .

(iv)             A femto (f) is ………… whereas a peta (P) is ………… .

(v)               Force is expressed in terms of unit newton (N.). Its expression in terms of SI basic units will be ………… .

(vi)             If joule is the unit of energy than the unit of power is

(vii)           There are ………… basic SI units.

(viii)         A block of substance weighs 48 ).lg. Its mass in SI units will be ………… .

 

III. Discussion Questions ———–

12. Match the following prefixes with their multiples

Prefixes                       Multiple

(i) yocto                       1024

(ii) atto                        1021

(iii) zetta                      10-24

(iv) yotta                     10 18

 

13. Convert each of the following:

(i) 456 run to metres                (ii) 45.6 mL to microlitres

(iii) 10 mg to kilograms           (iv) 50 km/h to metres per second.

 

14. Density is usually reported as grams per cubic centimetre. Convert this to SI unit of density. Indicate clearly the conversion factor used.

15. Convert the following into metre

(i) 7 nm (diameter of small virus)

(ii) 40 Em (thickness of milky way galaxy)

(iii) 1.4 Gm (diameter of sun)

(iv) 41 Pm (distance of nearest star).

 

16. Convert into kilogram

(i) 0.91 X l0-27 (mass Of Electron)

(ii) 1 fg (mass of human DNA molecule)

(iii) 500 Mg (mass of Jumbo jet)

(iv) 3.34 x 10-24 g (mass of hydrogen molecule).

 

17.  Define precision and accuracy.

18.Give the unit of the final answer obtained after each of the following operations:

(i) A density in gram per cubic centimetre is divided by a mass in gram.

(ii) A volume in cubic centimetres is divided by an area in square metres.

(iii) A mass in kilograms is multiplied by velocity in metres per second and divided by energy in joules.

 

1 Study the number of significant figures in· each of the following:

(i) 2.56 X 103              ‘(ii) 256            (iii) 5000

(iv) 0.00256                 (v) 0.0320        (vi) 13.560.

 

20. A block of wood having the dimensions 10 cm x 5 cm x 20 cm weighs 1.5 kg. What is the density of wood, expressed in grams per cubic centimetre?

21. Express the following SI base units using power of 10 notation

(i) 1.35 mm      (ii) l day           (iii) 6.45 rnL

(iv) 48 ).lg       (v) 0.0426 in.

22. Vanadium metal is added to steel to impart strength. The density of Vanadium is 5.96 g/cm3. Express in SI unit (kg/m3).

23 Can you make a measurement that’s very precise, but not very accurate?

24. Your partner uses a ruler to measure the length of a pencil and states that the length is 20.35232403 cm. What is your response to the given precision?

25. Outline the steps of a scientific method.

26. The mass of moon is 7.3 x 1023 kg. If a student reports the mass as 6.9 x 1022 kg, what is the accuracy of his calculation?