Lesson overview
Measuring and the pendulum: How can you time one swing of a pendulum accurately?
Read a rule and a measuring cylinder without parallax or zero errors, then time a pendulum with your own finger on the stop-clock: one swing, then twenty, then other lengths, and plot period against length.
Suggested sequence
- Lesson 1 · Read the scale. Reading rulers and measuring cylinders, and measuring small distances by multiples. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Time the swing. Timing with clocks and timers, and the period of a pendulum from many swings. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 2 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 2 questions, 15 min, lesson closed.
Learning goals
Part 1: Read the scale
- Describe how to use a ruler and a measuring cylinder to find a length or a volume (1.1.1)
- Find the average size of a small distance by measuring a multiple of it (1.1.3)
Part 2: Time the swing
- Describe how to measure time intervals with clocks and digital timers (1.1.2)
- Find the average value of a short time, such as the period of a pendulum, by timing many oscillations (1.1.3)
- Record readings in a table with quantity / unit headings and consistent precision, plot them on a graph and describe the pattern
Misconceptions to listen for
- “The length is the reading at the far end, 6.4 cm.” — That is only true when the object starts at zero. This key starts at the 1.0 cm mark, so subtract 1.0 cm.
- “Add the starting mark: 7.4 cm.” — The first centimetre of the ruler is not part of the key. Subtract the starting reading from the end reading.
- “6.4 mm, because the marks are millimetres.” — The numbered marks on this ruler are centimetres. And the key starts at 1.0 cm, so subtract: 6.4 cm − 1.0 cm = 5.4 cm.
- “8.0 ÷ 40 = 0.2, so one coin is 0.2 mm.” — 0.20 is the answer in centimetres, because the stack was measured in centimetres. In millimetres: 80 mm ÷ 40 = 2.0 mm.
- “Multiply: 8.0 × 40 = 320.” — One coin is much thinner than the whole stack, so divide the height of the stack by the number of coins.
- “Read the top edge, where the water touches the glass.” — The water climbs the glass at the edges, so the edges are higher than the true level. For water, read the bottom of the meniscus.
- “Look down from above so you can see the whole scale.” — From above, your line of sight crosses the scale at the wrong mark. That is parallax. Bring your eye level with the surface.
- “4.0 ÷ 250 = 0.016, so one sheet is 0.016 mm.” — 0.016 is the thickness in centimetres, because the stack was measured in centimetres. Convert: 4.0 cm = 40 mm, and 40 mm ÷ 250 = 0.16 mm.
- “Divide the number of sheets by the thickness: 250 ÷ 40 = 6.25.” — That is how many sheets fit in each millimetre, not the thickness of one. Thickness of one = total thickness ÷ number of sheets.
- “33 cm³, because that is where the water reaches the glass.” — The edges climb the glass, so they read too high. Read the bottom of the meniscus: 32 cm³.
Scope
Using rulers and measuring cylinders to find a length or a volume (1.1.1), measuring time intervals with clocks and digital timers (1.1.2), and finding the average of a small distance and a short time by measuring multiples, including the period of a pendulum (1.1.3), with the practical skills of tables and graphs. Vectors and scalars (1.1.4–1.1.7) are in the Resultant force module.