大象传媒

Key points

  • Developing a method is an important part of planning an investigation.
  • In an experiment, evaluate the validity of the steps leading up to the conclusion for it to be valid.
  • Random and systematic errors can contribute to the uncertainty of a measurement.

What is the name of a set of instructions that is followed when doing an experiment?

Back to top

Video

Watch this video on how writing a scientific method helps to get the correct amount and quality of data.

While you are watching, look out for the difference between types of errors that can happen.

Back to top

Writing a method

Scientists need to be able to clearly show how they carry out experiments and what they find out. When this is done properly, other scientists can check their work to find strengths and weaknesses with the experiment.

A describes how an experiment is carried out. It should contain a set of written instructions with numbers or letters to show the order in which the steps are carried out.

A diagram can be included to show how the experiment should look when it鈥檚 set up.

Each step should describe one action during the experiment. The used should be described, using scientific terms. Everything that was done to complete the whole experiment should be listed in the method, so somebody else could follow it and get a similar outcome.

Here is an example method for heating different volumes of water using a Bunsen burner.

Two school boys conducting experiment using a bunsen burner; both are wearing goggles.

What can be used alongside a list of numbered instructions in a method to make the experiment clearer?

Back to top

Accurate and precise data

The measurements that are taken in an experiment are called data. It is important to collect data that is and .

Accuracy is how close a measurement is to its . To make sure data is accurate, calculate a . Make sure that are not included in the calculation.Precision is how close are.

An illustration of dart-boards showing accuracy and precision variables.
Figure caption,
Accurate measurements may or may not be precise, and similarly, precise measurements may or may not be accurate.

If repeat measurements are similar, the data is said to be .If someone else does the investigation and gets similar results, the data is said to be .

If results are repeatable and reproducible, it can help lead to conclusions. Valid conclusions are drawn from valid data.

What word is used to describe a result that is close to its true value?

Back to top

A step-by-step guide on planning an experiment

Image gallerySkip image gallerySlide 1 of 6, Person doing science experiment - plotting results on a graph - test tubes to left, Plan an experiment well to get accurate and precise data. Without good quality data, conclusions won't be meaningful.

True or false?

If an experiment is planned well, the data produced after following the method is more likely to be precise and accurate.

Back to top

Types of error

Errors can happen when taking a measurement, usually leading to a spread in data. There are two types of error that affect scientific measurements: and .

Random error

This can alter the spread of data and cause outliers, as some measurements may be affected and not others. This can happen when equipment isn't used properly or a reading is taken incorrectly during measurements.

An example of this is . This is caused when a measurement is not taken at eye level. The reading recorded can end up being too high or low.

A ruler on the left with three lines coming from it to three positions of eyes, showing how a reading can be read too high or too low depending on where the eye is.
Figure caption,
Parallax error is caused by a student not reading the measurement at eye level. It can lead to the reading being too high or too low.

Systematic error

This can make measurements less accurate. It may happen if equipment is not used properly and can cause each result to differ by the same amount.

Examples of systematic error include not resetting a mass balance to zero and measuring from the end of a ruler instead of from zero.

Name the two types of error that can happen during an experiment.

Back to top

Test your knowledge

Quiz - Planning an experiment

Back to top

Play the Atomic Labs game! game

Try out practical experiments in this KS3 science game.

Play the Atomic Labs game!
Back to top

More on Working scientifically

Find out more by working through a topic