Year 7 Science · Unit 4 · Lesson 4
Master Worksheet
Learning Goals
Compare the instruments
Three balances are tested by weighing the same object, which has a true mass of 50.0 g. Study the data table, then answer the questions below it.
| Balance | Smallest step it shows | Reading for the 50.0 g object |
|---|---|---|
| Balance X | 1 g | 50 g |
| Balance Y | 0.1 g | 50.0 g |
| Balance Z | 0.1 g | 53.4 g |
(a) Which two balances are the most sensitive, and how can you tell from the table?
(b) Which balance is sensitive but not accurate? Explain your choice.
Plan a fair measurement
Scenario
Your class is investigating how much water evaporates from an open dish left on a sunny windowsill over one school day. You expect the change to be quite small, perhaps only a few grams. You have a measuring cylinder marked in 1 mL steps, a digital balance reading to 0.01 g, kitchen scales reading to the nearest 1 g, and a stopwatch. Your job is to choose the right instruments and explain why, thinking about range, sensitivity and accuracy.
(a) Which instrument would you use to measure how much water is lost, and why is its sensitivity important when the change is small?
(b) Describe your method. Explain what you would measure at the start and end, how you would read the instrument correctly, and how you would work out the change.
(c) Evaluate this statement: "A digital instrument is always better than an analog one because it gives a number." Do you agree? Justify your answer using the ideas of range, sensitivity and accuracy, and give a real example.
Wrap Up
In one sentence, what was the main idea of this lesson?