Topic Two (1.2): Estimation
Introduction
Enrico Fermi was an Italian Physicist who created the world’s first nuclear reactor. He would amaze his colleagues by making very accurate estimations of experiments without knowing the exact measurements. He made calculations using only the power of ten for each quantity. For example, imagine someone asked you “How many ants would it take to make a line which is 10 metres long?”. We can start by finding the nearest power of ten for the length of an ant, would it be 10–1m, 10–2m or 10–3m ? Well ants are certainly shorter than 10 cm and longer than 1 mm, so we can say 1 cm (10–2m). Now divide 101m (10m) by 10–2m (0.01m) and we get an answer of 1,000 ants. This works for pretty much anything that equations can be used to calculate and has led to the famous Drake Equation which is used to estimate the amount of Intelligent alien civilisations in the Milky Way Galaxy.
Skills of estimation are invaluable for being aware whether results are reasonable for a situation. Use this skill throughout the course, and it will rescue you from a lot of errors!
Reading
Edexcel AS/A Level Physics Student Book 1 pages 12 to 13
Tasks
Complete the following:
- Read pages 12 to 13 of the textbook.
- Complete the questions on page 13. You will find the answers in General Resources under the heading Textbook Answers.
Extend
WATCH – Drake Equation Visualized by Carl Sagan (YouTube) Links to an external site.
Top Tips
Make sure that you understand the following key points:
- We don’t need the first part of the standard form number to make estimations. For example, the height of an average human is 1.7 x 100 metres, but we can just say 100m.
- By eliminating the first part of the standard form number we are rounding up or down. But when we use the rounded powers to calculate an estimation all of the ‘roundings’ cancel out and we get a surprisingly accurate result.
- Use estimation to always stay aware whether values are reasonable in context. If not, do a careful check for errors!
Key Terms
Add the following key terms with definitions to your word list:
- Standard form
- Power of ten