Oscillations
Class 11 · Physics
4 ideas in Class 11 Physics, explained in plain words, with games and quizzes to practise.
Periodic Motion and SHM Basics
Part of: Rhythm and Simple Harmonic Motion
Repeating motion is periodic, timed by period and frequency. Simple harmonic motion is the special sine-form repeat about a mean, fixed by amplitude, angular frequency and starting phase. Circle projections and combined sines all trace it.
Why it matters. Clocks, hearts, bridges and radios tick on repeats. Sorting true SHM from casual repeats guides every later analysis.
Formulas
- Frequency = 1 / period
- Angular frequency w = 2 pi x frequency
Key words
- Periodic motion
- : Repeating motion timed by period and frequency.
- Period
- : Time for one full repeat.
- Frequency
- : Repeats per second, measured in hertz.
- SHM
- : Sine-form repeat about a mean position.
- Phase constant
- : The marker fixing the cycle position at time zero.
Try it in two minutes
- Time ten heartbeats and find the rate.
- Swing a pendulum and count cycles.
- Sketch a sine wave and mark its repeat.
Try at home. Time a fan's rotation and a dripping tap.
Velocity, Acceleration and Force in SHM
Part of: Rhythm and Simple Harmonic Motion
SHM speed peaks at the mean and vanishes at the ends; acceleration peaks at the ends aimed home, following minus frequency-squared times displacement. The force behind it is minus stiffness times displacement, a straight line through origin with negative slope.
Why it matters. One sign rule predicts every extreme: fastest middle, hardest pull at ends. It diagnoses SHM from any graph.
Formulas
- a = - w^2 x
- v = w root(A^2 - x^2)
- F = - k x
Key words
- Restoring force
- : The home-pulling force, minus stiffness times displacement.
- Amplitude
- : The farthest reach from the mean.
- Mean position
- : The centre about which SHM swings.
- Extreme position
- : A turning end where speed vanishes.
Try it in two minutes
- Watch a swing: fastest low, still at tops.
- Feel spring pull grow with stretch.
- Plot pull against stretch and note the slope.
Try at home. Time a mass on a band at middle versus ends.
Energy in SHM
Part of: Energy, Pendulums and Resonance
Energy swaps between motion and spring storage: kinetic rules the mean, storage rules the ends, and each peaks twice per cycle. The total is half stiffness times amplitude squared, fixed for the whole dance.
Why it matters. Energy shares explain speed anywhere without clocks. One constant total tames every position.
Formulas
- E = (1/2) k A^2
- U = (1/2) k x^2; K = (1/2) k (A^2 - x^2)
- vmax = A w
Key words
- Elastic potential energy
- : Stored spring energy, peaking at the ends.
- Kinetic share
- : Motion energy, peaking at the mean.
- Total mechanical energy
- : Fixed sum, half stiffness times amplitude squared.
- Damping
- : Friction bleeding amplitude and energy.
Try it in two minutes
- Release a spring from rest and watch it race mid-way.
- Mark where motion looks fastest.
- Halve the pull and quarter the energy.
Try at home. Compare bounce heights from two pull lengths.
Pendulum, Damping and Resonance
Part of: Energy, Pendulums and Resonance
Small pendulum swings time two pi root length over gravity; a metre ticks about two seconds. Friction bleeds amplitude while pace holds for light damping. Matched driving builds giant swings, which engineers dodge and radios exploit.
Why it matters. Clocks, bridges, vehicles and tuners all live here. Matching rhythm is power; mismatching is safety.
Formulas
- T = 2 pi root(l / g)
- Length grows with period squared: l = g (T / (2 pi))^2
- Resonance needs driving at natural frequency.
Key words
- Simple pendulum
- : A small-angle swinger timing two pi root length over gravity.
- Seconds pendulum
- : A metre-long pendulum ticking two seconds.
- Resonance
- : Giant swings from driving at natural pace.
- Damped motion
- : Amplitude decay with pace nearly held for light damping.
Try it in two minutes
- Time long and short pendulums.
- Push a swing off-rhythm versus on-rhythm.
- Watch ripples die after stirring stops.
Try at home. Tune pushes to grow a swing highest.
What your child will practise
- Energy in SHM: Jungle Quick Fire (Quick Fire)
- Pendulum, Damping and Resonance: Candy Puzzle (Clue Puzzle)
- Pendulum, Damping and Resonance: Candy Quick Fire (Quick Fire)
- Periodic Motion and SHM Basics: Desert Quick Fire (Quick Fire)
- Velocity, Acceleration and Force in SHM: Space Puzzle (Clue Puzzle)
- Quiz: Energy in SHM (8 questions)
- Quiz: Pendulum, Damping and Resonance (8 questions)
- Quiz: Periodic Motion and SHM Basics (8 questions)
- Quiz: Velocity, Acceleration and Force in SHM (8 questions)