Practical: circular motion on a string
G5.4
By the end of this lesson you should be able to
- Investigate the net forces acting on an object undergoing horizontal circular motion on a string. G5.4
Key ideas
- Aim: investigate the net force on an object in horizontal circular motion (G5.4).
- Set-up: a bung whirled on a string through a tube, with a hanging mass M providing the tension (≈ Mg).
- Vary the hanging mass (or radius); time 10–20 revolutions to find T.
- Analysis: from \(Mg = 4\pi^2 m r/T^2\), plot \(T^2\) against 1/M (or against r) and compare the gradient with theory.
- Evaluate: keeping r constant, friction at the tube, the string not being horizontal.
Key formulas (QCAA formula book notation)
\[
M g = \frac{4\pi^2 m r}{T^2}
\]
Common mistakes
- Timing a single revolution.
- Letting the radius drift during a trial.
Do
- Read: Textbook (Oxford Physics for Queensland Units 3 & 4) section 4.4
- Do: Practical 4.4 questions
- Data skills: Data test skills and practice
Try it
Further reading
- OpenStax College Physics 2e Ch. 6 Uniform circular motion and gravitation (OpenStax, CC BY 4.0)
- Full topic notes: Gravity & Motion