Lesson focus: Reliable measurements depend on choosing equipment with suitable scales and unitThe agreed measure written after a number, such as metres (m), seconds (s) or grams (g)..
Select measuring equipment and record a measurement with an appropriate unit and precision.
Build on earlier learning
Introduction and safetyRevisit how measurements become evidence in a scientific investigation.
Practical
Measuring with laboratory equipment
- Choose a measuring cylinder whose scale suits the volume: 10 cm³ for small volumes, 100 cm³ for larger ones.
- Read the bottom of the meniscus at eye level.
- Measure a mass on a balance after zeroing it with the empty container (tare).
- Record a temperature only when the thermometer reading has stopped changing.
Record: A table of each quantity with its unit and the resolution of the instrument used.
Safety: Carry glassware with two hands and report breakages; do not pick up broken glass.
You will be successful when you can…
- Match common apparatus to the quantity it measures.
- Distinguish range, scale division and resolution.
- Read an analogue scale without parallax error.
- Record a value with a unit and sensible precision.
Words that carry the science
- quantity
- A property that can be measured, such as mass, time or temperature.
- unit
- An agreed standard used to state a measurement.
- range
- The lowest to highest values an instrument can measure.
- resolution
- The smallest change an instrument can display or distinguish.
- parallax
- A reading error caused by viewing a scale from an angle.
Choose, read and record measurements
01Match the tool to the quantity
A ruler measures lengthHow long something is, measured in metres (m), centimetres (cm) or millimetres (mm)., a balance measures massHow much matter (stuff) is in an object, measured in grams (g) or kilograms (kg); it stays the same wherever the object is, unlike weight., a measuring cylinder measures volumeHow much space something takes up, measured in cubic centimetres (cm³) or millilitres (mL)., a thermometer measures temperatureHow hot or cold something is, measured in degrees Celsius (°C). and a stopwatch measures timeHow long something takes, measured in seconds (s), minutes or hours.. The correct unitThe agreed measure written after a number, such as metres (m), seconds (s) or grams (g). tells the reader what the number means.
Choose an instrument whose rangeThe spread from the lowest to the highest value, such as the values an instrument can measure or the values in your results. includes the expected value. A 10 mL cylinder cannot measure 40 mL, however fine its scale.
02Use the scale division
The smallest marked interval sets a sensible resolutionThe smallest change a measuring instrument can show, such as 1 mm on a ruler.. On a cylinder marked every 1 mL, readings such as 27 mL are defensible; 27.000 mL suggests information the scale does not provide.
Timing by hand has the same problem. A stopwatch may show 0.01 s, but a person takes about 0.2 s to react and press the button, so those last digits are not really known.
For an analogue scale, read at eye level. For liquid volume, use the correct part of the meniscus specified for that liquid—usually the bottom of the concave meniscus for water.
03Record evidence consistently
Put the unitThe agreed measure written after a number, such as metres (m), seconds (s) or grams (g). beside the table heading, not after every value. Use consistent precision when readings come from the same instrument.
Check for zero errorWhen a measuring instrument does not read zero when it should, so every reading is wrong by the same amount. before measuring: for example, tare a balance so it reads zero with the empty container. A measurement should then be recorded immediately and honestly, not changed to match an expected result.
Suitability depends on the quantity, expected range and useful resolution.
- 30 cm rulerLength; rangeThe spread from the lowest to the highest value, such as the values an instrument can measure or the values in your results. 0–30 cm; divisions commonly 1 mm.
- 100 mL cylinderLiquid volume; range 0–100 mL; read the marked divisions.
- Digital balanceMass; check the displayed resolution and tare before use.
- ThermometerTemperature; immerse the sensing region and read the stated unit.
Read a measuring cylinder
The bottom of a water meniscus lies halfway between 36 mL and 38 mL on a scale marked every 1 mL.
- Identify adjacent marked values: 36 mL and 38 mL.
- Count the divisions: the halfway division represents 37 mL.
- Read at eye level to avoid parallaxA reading mistake made when you look at a scale from an angle instead of straight on..
- Record 37 mL; do not invent unsupported decimal places.
How to make the reasoning visible: State the value and unit, with precision justified by the scale.
Apparatus decision table
Choose the most suitable option and justify it using range or resolution.
| Task | Option A | Option B | Better choice |
|---|---|---|---|
| Measure 18.4 g | Kitchen scale to nearest 1 g | Balance to nearest 0.1 g | Balance |
| Measure 8 mL | 10 mL cylinder, 0.2 mL divisions | 100 mL beaker, 20 mL marks | 10 mL cylinder |
| Time a 12 s reaction | Wall clock, 1 min marks | Stopwatch, 0.01 s display | Stopwatch |
| Measure 42 °C water | Thermometer, −10 to 110 °C | Room thermometer, 0 to 40 °C | −10 to 110 °C thermometer |
You need to measure 8 mL of liquid. Why is the 10 mL measuring cylinder better than the 100 mL beaker?
A stopwatch shows a time of 12.34789 s. Does writing all of those digits make the time more accurateClose to the true value, like a scale that shows exactly 100 g for a 100 g mass. (closer to the true value)?
Use the table. Why is the room thermometer (0 to 40 °C) not suitable for measuring 42 °C water?
Check your understanding
Answer from memory, then check against the suggested answer.
What does the range of an instrument tell you?
What is resolution?
How do you avoid parallax error (a wrong reading from looking at the scale at an angle)?
Which instrument measures mass?
Which instrument measures the volume of a liquid accurately?
You need to measure 23.6 mL of water. You can use a 25 mL cylinder with marks every 0.2 mL, or a 250 mL beaker with marks every 50 mL. Which should you use? Give a reason.
A balance shows mass to 0.01 g. With nothing on it, it reads 2.00 g. Will the student’s results be correct? Explain.
You need to measure 50 cm of string and 0.5 mm of wire thickness. Would you use the same ruler for both? Explain.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A student needs to measure about 9 mL of liquid. They can use a 10 mL measuring cylinder with marks every 0.2 mL, or a 100 mL beaker with marks every 20 mL. Answer the parts to justify choosing the cylinder.
Is 9 mL inside the range of the cylinder (the smallest to biggest value it can measure)? Explain.
(1)Compare the gaps between the marks (the scale divisions) on the cylinder and the beaker.
(1)Why does this make the cylinder the better choice? Start: “Smaller gaps between the marks mean …”
(1)Total for this question: 3 marks
Command word: For justifyA command word: give a reason or evidence that backs up your choice or answer., make a choice and give the reason for it, using a comparison.