Measurements in Science – JSS1 Intermediate Science Lesson Note (First Term)

Why do we measure?

In everyday life, we measure things all the time. When you tell a tailor how long you want your trousers, or when you buy 2kg of rice, you are measuring.

In science, we cannot just say something is “big” or “heavy” because people have different ideas of what “big” means. We need Standard Units so that a measurement in Lagos is the same as a measurement in London or Tokyo.

The SI Units

Scientists all over the world use a system called SI Units (International System of Units). These are the “official” units of science.

Note: Although Kelvin is the SI unit for temperature, in our daily lives and in the lab, we often use Degrees Celsius (°C).

MEASURING LENGTH AND MASS

1. Length

Length is the distance between two points.

• Instruments: For short distances, we use a Metre Rule or a 30cm Ruler. For long or curved surfaces (like measuring your waist), we use a Measuring Tape. For very tiny things (like the thickness of a wire), scientists use a Micrometer Screw Gauge.

2. Mass

Mass is the amount of matter in an object. People often call it “weight,” but in science, mass is more accurate.

• Instruments: In the lab, we use a Beam Balance or an Electronic Scale.
• Units: While the SI unit is the Kilogram (kg), we use Grams (g) for smaller items.

MEASURING TIME AND TEMPERATURE

1. Time

Time tells us how long an event lasts.

• Instruments: We use a Stopwatch or a Stop-clock in the lab because they allow us to start and stop exactly when an experiment begins and ends.
• Units: Seconds (s), Minutes (min), and Hours (h).

2. Temperature

Temperature tells us how hot or cold an object is.

• Instrument: We use a Laboratory Thermometer.
• How it works: Most thermometers have a liquid inside (mercury or alcohol) that rises when it gets hot and falls when it gets cold.
• Safety Tip: Never use a clinical (body) thermometer to measure boiling water; it will bark/burst because it isn’t designed for such high heat!

ACCURACY AND ERRORS

In science, we want our measurements to be “Perfect,” but sometimes we make mistakes. These mistakes are called Errors.

How to be Accurate

1. Avoid Parallax Error: This is the most common mistake. It happens when you look at a scale from the side. To get the right reading, your eyes must be directly above the mark, at a right angle (90∘).
2. Zero Error: Always check if your instrument (like a scale) starts at 0 before you begin. If it starts at 0.1, your final answer will be wrong!
3. The Meniscus: When measuring liquids in a cylinder, the water curves at the edges. Always read from the bottom of the curve (the meniscus).

Class Activity

1. Use your 30cm ruler to measure the length of your Basic Science textbook. Write the answer in cm.
2. If a bag of beans is 50kg, what is the physical quantity being measured?
3. Why should you not look at a thermometer from an angle when taking a reading?

Teacher’s Corner

Encourage students to practice measuring the volume of water in a cylinder, specifically pointing out the “meniscus” (the dip in the water level).