A student wants to estimate the time it takes for a human heart to beat once. Explain how the student could arrive at a reasonable estimate, including a final value with appropriate units.

AQA A-Level Physics (7408) — 3.1.3 Estimation of Physical Quantities · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

Count the number of heartbeats in a known time interval, for example 60 s (1 min). Use a timer or watch to record the time accurately. Count the beats in that minute – a typical resting heart rate is about 60–80 beats per minute. Divide the time interval by the number of beats to obtain the period per beat: 60 s ÷ 70 beats ≈ 0.86 s per beat. Thus the heart takes roughly 0.75–1 s to beat once (≈0.8 s).

Examiner tips

  • Use the correct formula: period = time ÷ beats; don’t invert the rate.
  • State a realistic resting heart rate (60–80 bpm).
  • Show the calculation and give the unit seconds.

Common mistakes

  • Using the rate (beats per minute) directly as the period.
  • Giving the answer in minutes instead of seconds.
  • Not showing the division step or the chosen heart‑rate value.

Mark scheme (5 marks)

  1. Method: count the number of heartbeats (pulse beats) in a known time interval (e.g. 60 seconds / 1 minute)
  2. Uses a timer / clock / watch to measure the time interval accurately
  3. Divides the time interval by the number of beats to find the time per beat (correct method for calculating period from rate)
  4. States a reasonable value for resting heart rate used in the calculation, e.g. approximately 60–80 beats per minute
  5. Gives a final estimate of approximately 0.75–1 second per beat with correct unit (seconds)

Key terms in this question

units

Related

More Estimation of Physical Quantities questions

▶ Try answering this question with AI marking (free) →