Tuesday 27 March 2012

The Scientific Method

(Updated on 2/10/2013 to include latest SPM 2012 questions)

Analysing Scientific Investigations
·        Before the time of Galileo Galilei (1564 ~ 1642), natural phenomena were commonly explained by pure thinking alone – for this reason, physics was then also known as natural philosophy.

·        However, this pure thinking or philosophical approach had led to many false beliefs - among which were that:
·        Our Earth was flat;
·        Our Earth was the centre of the universe;
·        A heavier object would fall freely faster than a lighter object…

·        Galileo adopted the approach that all hypothesis put forth to explain a natural phenomenon must be systematically investigated by experiments to prove its validity before it can be accepted as a law of nature or theory of physics – this systematic approach in verifying the validity of a hypothesis by experiments was, in essence, the scientific method.  Galileo was thus regarded by many including Albert Einstein as the father of experimental physics and of modern science.

·        Using the scientific method, Galileo proved that all objects – heavy or light – would fall freely from the same point with the same acceleration, g, which depends on the gravitational field strength at that point. Earlier authoritative “pure thinking theory on free-falling objects” was therefore proven wrong.

·        Laws of nature and physic are formulated by an inductive process – that is, from hypotheses on specific cases which have been proven right by scientific experiments. (As a simple illustration: This is how the law of nature which states that “the Sun rises in the east” may come about by an inductive process:

Man noticed that each time he looks at sunrise, the Sun seems to rise in a particular direction. He noticed from his compass the direction is east. So, he offers the hypothesis that “the Sun always rises in the east”. In all subsequent occasions that he or others look at sunrise, the Sun is still observed to rise in the same eastern direction. Hence, his hypothesis is accepted as a law of nature.)

·        Once accepted as a law of nature or physics law, the law can be applied to make deductions or predictions for subsequent specific instances. (Thus, when lost in the jungle, Man can deduce that the direction in which the Sun rises must be the east because the accepted law of nature is that “the Sun rises in the east”.)

The Scientific Method – The Main Steps:

1.      Making Observation (of a natural phenomenon or event that interests us) using our 5 senses of sight, hearing, smell, taste and touch – for example, observing movement of a swing in a playground.

2.      Making Inference – i.e. making early conclusion or recognition on the existence of a relationship between 2 variables observed in the phenomenon – For example, after careful observation, concluding that the time taken for a swing to make a complete swing depends on the length of the swing - there is a relation between the variable length and the variable time of the swing. The former is known as the independent or manipulated variable and the latter, the dependent or responding variable.

3.      Identifying Problem – i.e. asking questions based on the inference made: For example, what exactly is the nature of the inferred relationship? How does the length of the swing affect the period of its swing? A scientific report on an experiment usually begins with the problem statement or aim of the experiment which is usually worded as follows: “To study (or investigate) how one variable ( the manipulated variable, say, the length of the pendulum) affects another variable (the responding variable,say, the period of its oscillation)”.

4.      Making Hypothesis – i.e. making an early intelligent guess or sensible general statement about the exact nature of the inferred relationship between the 2 variables. There are at least 2 different ways to state the same hypothesis. Take the pendulum swing for example again:
a)    the period of oscillation increases as the length of the pendulum increases – i.e. hypothesizing how the responding/dependant variable changes as the manipulated/independant variable changes; or,
b)   as the length of the pendulum increases, the period of oscillation increases – stating the changes in the manipulated/independent variable first before hypothesizing how the values of the responding/dependant variable will be affected.

5.      Identifying Variables – i.e. identifying all other variables that may affect the responding/dependant variable other than the variable already identified (i.e. the manipulated/independent variable) so that all other variables that can affect the responding/dependent variable are fixed, controlled or kept constant. Therefore, a scientific experiment must identify all 3 sets of variables:
a.       Manipulated/Independent Variables
b.      Responding/Dependent Variables
c.       Fixed Variables

(2009 P1 Q3 pg. 186 - Test on understanding of the 3 variables)
(2010 P1 Q2 pg. 230 - Test on understanding of the 3 variables)

6.      Controlling Variables – i.e. planning and deciding:
               i.            how to manipulate the independent variable;
             ii.            how to measure the responding/dependent variable; and
            iii.            how to keep the fixed variables constant.

7.      Planning Experiment – means determining:
a.       what apparatus, instruments and materials to use;
b.      the procedure of the experiment;
c.       the method of collecting data;
d.      the ways to analyse and interpret the collected data.

8.  Collecting Data – means
               i.      making observation and description of qualitative data; or
             ii.      taking measurement of quantitative data; and, recording the data systematically by tabulation:
a.       Top Row of Table Must Contain: 1) Name of Variable, 2) Symbol and 3) Unit of Measurement
b.      First Column Contains: Values of Manipulated Variable at Uniform Intervals & in Ascending or Descending Order
c.       Second Column (with sub-colums for repeated measurements and average values) for: Measured Values of Responding Variables
d.      Third Column, if any, for Values Derived From Responding Variables for Use in Plotting Graph
e.       Values in Each Column Must Be Stated to the Same Number of Significant Numbers or Decimal Places; But Derived Values May Have an Additional Number of Decimal Places.

9.  Interpreting Data – this is the part that involves the study of the recorded data, the making additional calculations where necessary and the drawing of graphs to see whether the relationship between the 2 variables is as originally hypothesized. Discussion is usually involved. The six common graphs, their meanings and how they look like:
               i.            Responding Variable Increases as Manipulated Variable Increases:
             ii.            Responding Variable Decreases as Manipulated Variable Increases
            iii.            Responding Variable Increases Linearly with Manipulated Variables
           iv.            Responding Variable Decreases Linearly with Manipulated Variable
             v.            Responding Variable is Directly Proportional to Manipulated Variable
           vi.            Responding Variable is Inversely Proportional to Manipulated Variable (i.e. Responding Variable is Directly Proportional to the Inverse or Reciprocal of Manipulated Variable)

(SPM 2006 P1 Q2 Pg. 48 on graph for F = kx)

(SPM 2012 P3 Q1(d) & (e) pg 375: Plot the graph of x against 1/a (as in x = λD/a) and state the relationship between x and 1/a )
* Any graph of y against 1/x - or x against 1/a as in the above SPM 2012 P3 Q1 -  which is a straight line with a positive gradient must not be described as "y is directly proportional to 1/x" because such a straight line graph will never pass through the origin as 1/x will never be zero (in the case of the SPM question, 1/a will never be zero). For such a graph, the relationship is: y increases linearly with 1/x (or, x increases linearly with 1/a in the case of the SPM 2012 P3 Q1(e))

1  10.  Making Conclusion – this involves making a statement on the findings of the experiment:
a.       Whether the inference made was correct; and,
b.      Whether the hypothesis put forth is valid or to be rejected.

1  11.  Writing Report – Writing a report on the whole experiment so that:
a.       Its findings can be critically evaluated by others; and, if necessary, the experiment can be repeated to verify its findings;
b.      The findings are recorded for understanding, use or application by others.

Relevant Past-Year Questions: Most Paper 3 questions are related to scientific method of investigation - of direct relevance to Form 4 Chapter 1 are:
  • SPM 2010 Paper 3 Q1 at Pg. 268
  • SPM 2009 Paper 3 Q1 at Pg. 220
  • SPM 2008 Paper 3 Q1 at Pg. 174

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