Physics you can pull, tune and listen to
Interactive experiments for undergraduate physics. Change a parameter and the graphs, animations and numbers respond at once. Every experiment shows the equation it solves.
Damped oscillator
Mass, spring and damper. Drag the block, change the damping and watch energy drain away.
ElectricityLRC circuit
Natural response with moving charge and energy bars, plus a resonance curve for a driven circuit.
WavesTravelling and standing waves
Frequency, wavelength and speed, transverse or longitudinal, and standing waves from a reflection.
AcousticsSound waves
Hear a tone, change its pitch and timbre, see the waveform and make beats with two tones.
LightWavelength and colour
Pick a wavelength and see its colour, frequency and photon energy. Try real laser and lamp lines.
Optics opens Ray Bench in a new tabRay Bench
Ray tracing for lenses, microscopes and telescopes, with aberrations and pupils.
Built for BU-CROCCS physics classes. Units are SI unless a control says otherwise. Use the tabs at the top to move between experiments; each one keeps its settings while this page is open.
Damped harmonic oscillator
A block of mass m on a spring of stiffness k, slowed by a damper with coefficient b. Drag the block to set where it starts.
Parameters
Results
Equation
Try this
- Set b = 0. The total energy line stays flat and the motion never decays.
- Press Critical damping. The block returns to zero as fast as possible without overshooting. This is how car shock absorbers and door closers are tuned.
- Double b beyond critical. The return gets slower again: the system is overdamped.
- Measure the time between two peaks and compare with the damped period 2π/ωd shown in Results.
- Quadruple the mass. By how much does the period change? Check T = 2π√(m/k).
LRC electrical oscillator
A capacitor charged to V₀ is connected at t = 0 to an inductor and a resistor. Energy sloshes between the capacitor's electric field and the inductor's magnetic field while the resistor turns it into heat.
Components
Results
Equations
Try this
- Set R = 0. The voltage oscillates forever at f₀ = 1/(2π√(LC)).
- Press Set R to critical (R = 2√(L/C)). The capacitor discharges fastest without ringing.
- Make C four times larger. The frequency halves. Check with the Results panel.
- Watch the energy bars: the capacitor and inductor trade energy twice per cycle, and the heat bar only grows.
- Copy the data and paste it into a spreadsheet to fit the decay envelope and find γ.
Driving source
Try this
- Slide the driving frequency through f₀. The current peaks and is exactly in phase with the source at resonance.
- Below f₀ the circuit is capacitive (current leads). Above f₀ it is inductive (current lags).
- Lower R. The peak gets taller and narrower: Q = f₀/Δf goes up.
- At resonance, the capacitor voltage is Q times the source voltage. Check VC in the table.
Travelling and standing waves
A sinusoidal wave on a 4 m string. Click anywhere on the string to track one point of the medium and see that it only moves up and down while the wave moves along.
Wave
With the speed fixed, raising the frequency shortens the wavelength (v = f λ).
Display
Results
Try this
- Follow the red point. It moves up and down; it never travels along the string. The wave carries energy, not matter.
- Lock the speed and double the frequency. The wavelength halves and the crest marker still moves at the same speed.
- Untick the lock and raise the wavelength alone. Now the speed v = fλ increases (a different medium).
- Add the reflected wave. Nodes (marked) never move and sit λ/2 apart. Track a point at a node and at an antinode.
- Switch to particles. Compressions travel, while each particle only oscillates about its home position.
Sound waves
Play a tone through your speakers or headphones, then change its frequency, waveform and loudness while you watch the pressure wave.
Tone
Beats
Two close frequencies interfere. You hear one tone whose loudness pulses |f₁ − f₂| times per second.
Air
Try this
- Sweep the frequency from 20 Hz upward. Where does the tone become audible on your speakers? Where does it disappear at the top? Hearing range narrows with age.
- Compare sine and square at the same frequency. Same pitch, different timbre: the square wave contains odd harmonics 3f, 5f, 7f…
- Turn on beats with Δf = 2 Hz and count the loudness pulses for 5 seconds. Musicians tune instruments by making beats disappear.
- Change the temperature. The speed of sound and the wavelength change, but the frequency (pitch) does not.
Wavelength and colour
Visible light runs from about 380 nm (violet) to 750 nm (red). Drag across the spectrum or type a wavelength to see the colour, frequency and photon energy.
Wavelength
Results
Equations
Try this
- Compare a red laser (650 nm) and a green laser (532 nm). Which photon carries more energy? Why does green look brighter at the same power?
- Go below 380 nm. Ultraviolet photons have more than 3.3 eV, enough to break chemical bonds, which is why UV causes sunburn.
- Go above 750 nm. Infrared is invisible but you feel it as heat. TV remotes use about 940 nm.
- Find the wavelength where the frequency is 600 THz. Check it with f = c/λ.