Tuesday, January 20, 2009



1.) Producing
a logical plan

a) Defining the problem

Involves identifying two measurable quantities that are related to each other and suggesting a clear statement of the task to be undertaken.

Example 1: How does the temperature of a squash ball affect its bounce?
The bounce of the squash could be associated with the height of rebound of the ball(measurable quantity)

A suitable statement of task can be: The two Measurable quantities,

Example 2:

You are to design an experiment to see if elastic bands are suitable to be used as a simple spring balance,

This task would be more clearly defined if we investigate how the extension of the elastic band is changed by the weight attached to it. If there is a direct proportionality between extension and weight, we can calibrate the elastic band to measure forces. hence, a simple spring balance.

A suitable statement of task can be
To investigate the relationship how much the elastic band is affected by the number of weights,

b) Identify Independent and Dependant variables

Example: The number of weights is the independent variable (x-axis)
The extension of the elastic band is the dependent variable. (y-axis)

c) Identifying Constant Variables

In practice, there are many independent variables that will affect a chosen dependent variable. To obtain a reliable insight into the relationship between two physical quantities, it is very important to identify these independent variables constant throughout the experiment.

Constant Variables

How to keep these variables constant

......... of ball

Use the same ball throughout the experiment

......... of material

Use the same ball throughout the experiment

.......... of impact

Ensure ball falls vertically

...... at which ball is released

Ensure ball is released at the same height for all readings.

d) Choose Appropriate Procedures
  1. Draw a labelled diagram of the experimental set-up
  2. List the apparatus needed of the investigation. Where appropriate, give a brief description of the features of the apparatus and its mode of operation.
  3. The experimental procedure should be step-by-step, logical and clear. It should be capable of meeting the goals expressed in the statement of task.
  4. A table of results with proper headings/units should be presented.
  5. Plot a graph to display the relationship between the dependent variable (plotted on y-axis) and the independent variable (plotted on x-axis)
  6. Several statements of precaution should be written. It should be able to answer two important questions, namely


    Precautions can fall into two categories:
    i) Precautions to ensure safety of experimenter and those around him/her.
    For example:

    Place a heavy weight on the retort stand to prevent it from toppling and hitting someone.
    ii) Precautions to ensure reliability of results.
    For example:

    Stir hot water continuously in order to obtain uniformity of temperature.

2.) Evaluating procedures and modifying plans

a) Evaluate the Plan and procedures

Discuss the degree to which your experiment could yield results that are reliable and accurate. Consider the following questions:

is there a need to simply procedures so that measurements can be reproduced with by another person?

Are the measuring instruments chosen appropriate?

Does the experiment produce results with a constant trend?

Are repeated measurements close to each other or differ widely?

How much scattering are there in the plotted graph?

Are the constants obtained from gradient and intercepts consistent with known accepted values?

b) Modifications and Improvements

eg1: Visual estimation of the rebound height could be replaced by the use of data loggers(such as motion sensor)

Increase the range of readings (eg. 50.0-90.0 cm to 20.0-90.0 cm)

Increase the number of readings within a certain range. This is necessary if your graph is a curve and more values are required around the turning point.

Modifying techniques in order to make the experiment as precise and reproducible as possible.

Modify techniques to avoid sources of error

Modify techniques to reduce random error.  

1 comment:

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