ConceptMechanics
← All conceptsSimple harmonic motion & mechanical waves
SHM restoring force F=-kx and a opposite to x, period of mass-spring/pendulum T=2·π·√L/g, displacement/velocity/acceleration sign relations on graphs; mechanical waves transverse/longitudinal, v=f·λ, frequency set by source (unchanged across media)
15 ways this goes wrong. Each one is a named misconception the questions are built to catch.
- Acceleration not opposite displacementTakes acceleration in the same direction as displacement, missing that a=-(k/m)x always opposes x.→
- Amplitude affects speedAssumes a larger-amplitude wave travels faster in the same medium.→
- Frequency changes across mediaBelieves a wave's frequency changes when it enters a new medium, where frequency is fixed by the source.→
- Max acceleration at equilibriumPlaces maximum acceleration at the center rather than at maximum displacement.→
- Max speed at the extremesPlaces maximum speed at the amplitude extremes instead of at the equilibrium position.→
- Medium particles travel with waveBelieves the medium's particles move along with the wave rather than oscillating about fixed positions.→
- Pendulum period depends on massThinks the simple pendulum's period depends on the bob mass rather than only on L and g.→
- Restoring force sign wrongWrites F=+kx (away from equilibrium) instead of the restoring F=-kx directed toward equilibrium.→
- SHM period depends on amplitudeBelieves a larger amplitude lengthens the period of an ideal SHM oscillator.→
- Spring period k/m invertedUses T proportional to √k/m instead of √m/k, inverting the mass and stiffness roles.→
- Total SHM energy oscillatesBelieves total mechanical energy varies through the cycle, rather than KE and PE interchanging at constant total.→
- Transverse/longitudinal swappedClassifies sound as transverse or a wave on a string as longitudinal, swapping the oscillation-direction relationship.→
- Velocity and acceleration same signAssumes velocity and acceleration always share a sign in SHM, ignoring that they oppose while the body moves back toward equilibrium.→
- Wavelength read off time graphReads wavelength from a displacement-time graph (which shows period) or period from a displacement-distance graph.→
- v=f·λ misusedRearranges v=f·λ incorrectly, e.g. λ=v·f, or treats frequency as inversely proportional to speed.→
