Learning Objective

In this lesson we will learn how scientific knowledge is accumulated through a rigorous and methodical process of inquiry.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe the steps involved in the scientific method.

  • Define qualitative and quantitative observation, inference and prediction.

  • Describe how a fair test is conducted, including independent and dependent variables, control variables, test groups and control groups.

  • Explain how the accumulation of scientific knowledge may lead to theories or laws, and differentiate between the two.

 

BUY THE YEAR 7 CHEMISTRY WORKBOOK

 

Introduction

  • Science is about making observations, interpreting and attempting to explain these observations, and then testing if our ideas about them hold true.
  • This accumulation of scientific knowledge and understanding follows a process of inquiry known as the scientific method.
  • The scientific method involves a series of steps:
    1. Making an observation.
    2. Making an inference and prediction based on the observation.
    3. Conducting an experiment to test the prediction.
    4. Developing a theory or law based on multiple experiments.

 
scientific method ongoing process

The scientific method is an ongoing process.

(Image: Whatiguana, Wikimedia Commons)

 

1. Making Observations

  • An observation involves noticing and recording a particular occurrence.
  • Being able to make careful and accurate observations is an important skill in science.
    We can formulate and test ideas based on our observations, thus gaining a better understanding of the world around us.
  • There are two types of observations: qualitative observations and quantitative observations.

 
microscope observation

Making an observation is the first step in the scientific method.

(Image: Yakuzakorat, Wikimedia Commons)

 

Qualitative Observations

  • Qualitative observations relate to qualities and involve descriptions.
  • They often involve our senses and include things like colour, odour or texture.
    For example, “the car is yellow”, “the fumes are pungent”, the “leaf is smooth”.
  • Qualitative observations are often subjective. That is, they can be interpreted differently by different people.
    For example, you might describe the colour of a stone or the sound of a bird quite differently to someone else.
    This can make analysis of qualitative observations more difficult than quantitative observations; nonetheless, they are an important part of the scientific process.

 
smell qualitative observation

Describing how something smells is an example of a qualitative observation.

(Image: Free-Photos, Pixabay)

 

Quantitative Observations

  • Quantitative observations relate to quantities and involve measurements.
  • They can be described with numerical values and units of measurement, and include things like mass, temperature or speed.
    For example, the “dog weighs 16.5 kg”, “the air temperature is “16 °C”, “the train is travelling at 80 km/hr”.
  • Quantitative observations are objective. That is, different people should make the same observation.
    For example, if you measured the height of the classroom door, you should get the same answer (or a very similar answer) as someone else in your class.
    This makes analysis of quantitative observations easier than qualitative observations; therefore, they are the most useful type of observation in the scientific process.

 
quantitative observation measurement

Quantitative observations usually involve measurements.

(Image: Júlio Reis, Wikimedia Commons)

 

2. Inferring and Predicting

  • Observations on their own are of little use in science until we analyse them.
  • An inference is an interpretation of an observation and an attempt to explain it.
    For example, “the dog weighs 16.5 kg, which is an increase of 1.5 kg, which means the new brand of dog food has probably caused it to gain weight”.
  • Once we have made an inference about our observations, we can use this to make a prediction, also known as a hypothesis.
    For example, “eating the new brand of dog food will cause dogs to gain weight”.

 
hypothesis dog eating food

A hypothesis is a prediction based on an observation.

(Image: Counselling, Pixabay)

 

3. Conducting a Fair Test

  • Once we have developed a hypothesis, the only way to find out whether it is true or not is by conducting an experiment and observing the results.
  • A key component of any scientific experiment is that it is a fair test, also known as a controlled experiment.
    This means that the experiment is designed in a way that gives a reliable and unbiased answer to the question being investigated.
    The design of an experiment is fundamentally important as it will have a big effect on the reliability of the results.
    A poorly designed experiment will yield outcomes with little significance, but a well-designed experiment can have very significant outcomes.

 
scales measurement fair test

A fair test is a scientific way of testing a hypothesis.

(Image: Skitterphoto, Pixabay)

 

Variables

  • In designing the experiment, the variables need to be identified.
  • A variable is any factor that can change during an experiment.
  • There are three kinds of variables: independent variables, dependent variables and control variables.
    We will look at these, using the above example about dog food.

 
variable fair test experiment

A variable is anything that can change during an experiment.

(Image: olafpictures, Pixabay)

 

Dependent and Independent Variables

  • The dependent variable is the factor being measured, to see if it changes.
    In the example, the dependent variable is the weight of dogs. We want to know whether it changes and by how much.
  • The independent variable is the factor that the investigator will change during the experiment, to see what effect it has on the dependent variable.
    In the example, the independent variable is the brand of dog food. We want to see if it affects the weight of dogs.

 
dog food weigh independent dependent variable

In an experiment testing the effect of different types of dog food on the weight of dogs, the independent variable is the type of dog food, and the dependent variable is the weight of the dogs.

(Image: eminens, Pixabay)

 

Control Variables

  • A fair test has only one independent variable.
    Otherwise, the results will be confusing, because if more than one independent variable is changed by the investigator, they will be unable to determine which one caused the change in the dependent variable.
    For example, if the investigator used different brands of dog food but also different amounts of dog food, they would not know whether any weight changes observed were caused by the brand of dog food or the amount of dog food, or whether it was a combination of both.
  • Therefore, every other factor that could change, but needs to be kept the same, should be identified.
    These factors are called control variables, as they need to be controlled (kept constant) by the investigator.
    So, other than the amount of dog food, additional control variables might include:
    • Breed of dog
    • Age of dog
    • Sex of dog
    • Whether the dog has been desexed or not
    • Length of time the experiment goes for
    • Number of dogs in the trial
    We don’t know whether these factors will affect weight gain, but we need to control for them just in case they do have an effect. We are only testing the effect of the brand of dog food.

 
control variables fair test

Any factor that could affect the dependent variable, other than the independent variable, must be kept constant.

(Image: skeeze, Pixabay)

 

Control Groups and Test Groups

  • A fair trial will therefore involve two types of groups: control groups and test groups.
  • A control group is the group where the independent variable has not been changed.
    There must be one control group in every fair test.
    In the example, this is the group that will be given the original brand of dog food.
  • A test group (also called an experimental group) is a group where the independent variable has been changed.
    There may be more than one test group in a fair test.
    In the example, this is one test group – the group that will be given the new brand of dog food.
  • When designing a fair test, the only difference between a control group and a test group should be the independent variable.
    All other factors, that is, all the control variables, must be kept consistent between the control group and test groups.
    For example, the test needs to be conducted either with the same breed of dog in each group or the same mix of breeds in each group. This way we can be sure that the breed of dog is not contributing to different results between the two groups.

 
food weight control test group

When setting up a fair test, the only variable that should differ between control groups and test groups is the independent variable.

(Image: jagdprinzessin, Pixabay)

 

Interpreting Results and Making Conclusions

  • Once an experiment has been conducted, the results can be analysed.
    In the example, this would include a conclusion about whether or not the brand of dog food had an effect on the weight of dogs.
    There are three possible conclusions:
    1. The brand of dog food had no effect.
    2. Therefore, the hypothesis is rejected.

    3. The brand of dog food had a clear effect.
    4. Therefore, the hypothesis is accepted.

    5. It was unclear whether the brand of dog food had an effect.
      This might be because there was only a small difference, and it was not clear whether this was due to the brand of dog food or just a result of chance.
    6. Therefore the hypothesis requires further testing, perhaps with larger groups or over a longer time period.

  • The analysis may also make some suggestions for further study. These might include:
    • Determining what component of the dog food was causing the increase in weight (if the results did show an increase).
    • Determining whether other factors contribute to weight gain (these could include any of the control variables).
  • So, the scientific process is ongoing.
    Each investigation will answer some questions, but also create new ones!

 
interpreting experiment result conclusion

Interpreting an experiment’s results can lead to a hypothesis being accepted or rejected.

(Image: PublicDomainPictures, Pixabay)

 

4. Development of Theories and Laws

  • When a hypothesis has been tested many times by different scientists, and the results are all in agreement, then a broader conclusion can be made.
    This conclusion can take the form of a theory or a law.
  • A scientific theory is an explanation of some aspect of the natural world that has been well-substantiated by multiple tests.
    It is the best interpretation based on current knowledge, but is subject to refinement or even rejection as new evidence is acquired.
    An example of a scientific theory is the atomic theory, which is a model that attempts to explain the structure of atoms, based on experimental evidence. This model has developed over hundreds of years and continues to evolve.
  • A scientific law is a descriptive generalisation about some aspect of the natural world that holds true all of the time.
    For example, Isaac Newton’s laws of motion describe the mathematical relationship between forces, mass and motion of objects. These laws are fixed and have not changed since they were first stated.

 
newton einstein gravity theory law

When hypotheses are repeatedly confirmed, theories or laws may be developed.

(Images: Godfrey Kneller, Wikimedia Commons; NASA/JPL-Caltech; F. Schmutzer, Wikimedia Commons)

 

Theories vs Laws

  • Although both theories and laws are developed from the scientific method, they are separate and non-interchangeable.
  • Theories are explanatory, mostly based on inferences – they deal with the “how”.
    They are generally broad in focus and are based on the accumulation of multiple sources of congruous evidence.
    They are comprehensive accounts of natural phenomena, but can never be proven.
  • Laws are descriptive, mostly based on observations – they deal with the “what”.
    They are generally narrow in focus and specific to a certain set of conditions.
    They do not require an explanation or mechanism, they are simply truths that have been proven by repeated testing.
  • Theories can change, but laws are unchangeable.
  • A theory can never become a law.
    For example, even though the vast majority of scientists agree that the evidence for evolution is overwhelming, it will always be a theory as we cannot travel back in time and conduct experiments that involve taking measurements over millions of years.

 

theory evolution                law gravity

Theories, such as theories about evolution, can change over time; laws, such as the laws of gravity, are unchangeable.

(Images: Daniel Mietchen, Wikimedia Commons; Dennis Nilsson, Wikimedia Commons)

 

Facts

  • A fact is simply an observation that is indisputable.
    For example, it is a fact that the Sydney Harbour Bridge was opened on the 19th March 1932.”
  • A scientific fact is an occurrence that has been repeatedly confirmed by testing.
    For example, it is a scientific fact that water is formed from the elements hydrogen and oxygen.
  • So in the context of the scientific method, quantitative observations are facts and laws are scientific facts, whereas hypotheses, inferences and theories are neither.

 
scientific facts

Facts are indisputable.

(Image: geralt, Pixabay)

 

Summary

  • The scientific method is a systematic approach that characterises the way in which scientific knowledge is acquired.
  • The main steps in the scientific method are:
    1. Making an observation.
    2. Making an inference and prediction.
    3. Conducting an experiment.
    4. Developing a theory or law.
  • An observation involves noticing and recording a particular occurrence.
  • Qualitative observations relate to qualities and involve descriptions. They are subjective and usually involve our senses.
    Quantitative observations relate to quantities and involve measurements. They are objective and involve numerical values and units of measurement.
  • An inference is an interpretation of an observation and an attempt to explain it.
  • A hypothesis is a prediction based on an inference.
  • A fair test or controlled experiment is an investigation that tests a hypothesis.
  • A variable is any factor that can change during an experiment.
    A dependent variable is a factor being measured during an experiment.
    An independent variable is the factor being investigated during an experiment, by observing what effect it has on the dependent variable.
    A control variable is any factor kept constant during an experiment.
  • A test group (experimental group) has a modified form of the independent variable in an experiment.
    A control group has an unmodified form of the independent variable in an experiment.
  • Following an experiment, a hypothesis is either accepted or rejected, or may require further testing if the results are inconclusive.
    Experimental results often create new questions that can be tested.
    The acquisition of scientific knowledge is a continual process.
  • When a hypothesis is tested multiple times with the same result, it may lead to the development of either a theory or a law.
  • A theory is an explanation of some aspect of the natural world that has been well-substantiated by multiple tests.
    A theory is an interpretation that can evolve as new evidence is acquired. However, it can never become a law.
  • A law is a descriptive generalisation about some aspect of the natural world that holds true all of the time.
    A law is constant and not subject to change.
  • A scientific fact is an occurrence that has been repeatedly confirmed by testing.

 
old science books

(Image: jarmoluk, Pixabay)

 

(Header image: Blue Planet Studio, Adobe Stock)

 

BUY THE YEAR 7 CHEMISTRY WORKBOOK