Physical Quantities and Measurement Techniques

2026 Syllabus Objectives

By the end of this topic, you should be able to:

Core:

  1. Describe the use of rulers and measuring cylinders to find a length or a volume
  2. Describe how to measure a variety of time intervals using clocks and digital timers
  3. Determine an average value for a small distance and for a short interval of time by measuring multiples (including the period of oscillation of a pendulum)

Supplement: 4. Understand that a scalar quantity has magnitude (size) only and that a vector quantity has magnitude and direction 5. Know that the following quantities are scalars: distance, speed, time, mass, energy and temperature 6. Know that the following quantities are vectors: force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength 7. Determine, by calculation or graphically, the resultant of two vectors at right angles, limited to forces or velocities only

1. Measuring Length

https://cambridgeassistant.com

Using a Ruler

A ruler (also called a metre rule) is used to measure straight lengths, usually up to 1 metre or 100 centimetres.

How to use a ruler properly:

  • Place the ruler alongside the object you want to measure
  • Make sure the zero mark of the ruler lines up with one end of the object
  • Position your eye directly above the measurement mark (perpendicular to the scale)
  • Read the measurement where the other end of the object lines up with the ruler
  • A typical ruler can measure to the nearest millimetre (mm) — this is called its precision (the smallest unit it can measure)

Avoiding parallax error: When you read a measurement, your eye must be positioned directly above the scale, looking straight down at it. If you look at an angle, you'll get a different (wrong) reading. This mistake is called parallax error. Think of it like this: if you look at a pencil on a ruler from the side instead of from above, the pencil will appear to be at a different position on the ruler.

Measuring small distances accurately: Sometimes you need to measure something very small, like the thickness of a piece of paper. One sheet is too thin to measure accurately. Instead:

  1. Stack many sheets together (e.g., 100 sheets)
  2. Measure the total thickness of the stack
  3. Divide by the number of sheets to find the thickness of one sheet

This method gives you a much more accurate result because it reduces the effect of small measurement errors.

Using Measuring Cylinders

A measuring cylinder is a container with measurement markings on the side, used to measure the volume (amount of space) of liquids.

How to use a measuring cylinder:

  • Pour the liquid into the cylinder
  • Place the cylinder on a flat, level surface
  • Position your eye level with the surface of the liquid
  • Look at the bottom of the curved surface (called the meniscus)
  • Read the volume at this point

Why measure at the bottom of the meniscus? When you pour water or other liquids into a measuring cylinder, the surface curves slightly. The liquid climbs up the sides of the glass a tiny bit, creating a curve. Always read from the bottom of this curve for an accurate measurement.

Measuring the volume of irregular objects: You can also use a measuring cylinder to find the volume of solid objects that have irregular shapes (like a stone or a key):

  1. Fill the cylinder with water and record the volume (V₁)
  2. Carefully lower the object into the water
  3. Record the new volume (V₂)
  4. The volume of the object = V₂ - V₁

For objects that float: Use a sinker (a small heavy object) to push the floating object underwater:

  1. Measure the volume of water + sinker (V₁)
  2. Add the floating object and measure water + sinker + object (V₂)
  3. Volume of floating object = V₂ - V₁

Sign in to view full notes