Everyday Physics
Why the sky looks a certain color at a given sun angle, how buoyancy works in a bathtub experiment, or whether a smartphone projector setup will actually focus: physics questions you'd run into day to day, less formal than the rest of the physics subcategories.
Calculators & Tools
Sun Angle Calculator
The sun angle calculator computes solar elevation (altitude above the horizon), azimuth (compass bearing), declination, hour angle, solar noon, air mass, and shadow length for any latitude, longitude, date, and time. It uses the standard NOAA solar position algorithm: declination from the day of year, equation of time for clock-to-solar-time conversion, and the spherical trigonometry equations relating elevation to declination, latitude, and hour angle. Additional outputs include sunrise and sunset times, day length, optimal solar panel tilt by season, and golden hour windows for photography. The hour-by-hour table shows all positions across the full day.
Sunrise Sunset Calculator
The sunrise and sunset calculator computes the precise times of sunrise, sunset, solar noon, civil twilight, nautical twilight, astronomical twilight, golden hour, and blue hour for any latitude, longitude, and date. It uses the NOAA solar position algorithm with the standard 0.833-degree atmospheric refraction correction that shifts sunrise earlier and sunset later by 2 to 5 minutes compared to the geometric horizon. All six twilight periods (morning and evening for each type) are computed by solving for the hour angle at which the sun crosses each depression angle. Day length, azimuth at sunrise and sunset with compass direction, the equation of time correction, and a day-length trend compared to the previous day are included. A practical use-cases panel translates solar times into Islamic prayer windows, hunting and fishing legal light, Jewish Shabbat candle-lighting, and photographer golden-hour windows. An annual calendar table shows weekly sunrise, sunset, and azimuth data for the full year.
Buoyancy Experiment Calculator
This calculator applies Archimedes' principle to find buoyant force, net vertical force, apparent weight and whether an object floats, sinks, or achieves neutral buoyancy. Enter volume directly or compute it from sphere, cylinder, rectangular prism, or cone dimensions. Choose from ten built-in fluids including fresh water, seawater and mercury, or enter a custom density. Enable the mass or material section to unlock float/sink verdicts, percentage submerged, and a step-by-step worked solution.
Smartphone Projector Calculator
A DIY smartphone projector uses a single convex lens to form a real, inverted image of the phone screen on a wall or screen. The thin lens equation (1/f = 1/do + 1/di) links the focal length of the lens, the phone-to-lens distance, and the throw distance. Magnification equals the ratio of those two distances, and the projected image diagonal equals the phone screen diagonal multiplied by the magnification. This calculator solves for any unknown, outputs exact box dimensions for the build, and rates projected brightness based on magnification.
Flat vs. Round Earth Calculator
This calculator uses exact spherical geometry to compute hidden height, surface drop, and horizon distance for any observer and target combination. Enter distance, observer eye height, and optional target height to see what a spherical Earth predicts versus what a flat Earth predicts. A side-by-side globe vs. flat comparison shows the difference instantly. Toggle atmospheric refraction to see how standard air bending extends the horizon by roughly 7%. Four modes cover hidden height, horizon distance, surface drop, and two-point line-of-sight.
Hair Diffraction Calculator
This calculator measures the diameter of a human hair using single-slit laser diffraction. Enter your laser wavelength (with built-in presets for red, green, blue and violet pointers), the distance to the screen, and the fringe spacing you measured. It returns the hair diameter in micrometres using the exact formula d = m*lambda/sin(theta), plus an uncertainty estimate from your ruler precision. Multi-order averaging mode lets you enter readings for m = 1 through 4 to significantly reduce random error, and a reverse mode calculates the laser wavelength from a known calibration fibre.
Immersed Weight Calculator
An object submerged in fluid experiences a buoyant force equal to the weight of fluid it displaces, reducing its apparent weight by exactly that amount. The two-weight method -- weighing an object in air and again fully submerged -- lets you calculate its density without measuring its volume directly, a technique Archimedes used to test the king's crown. For body composition, hydrostatic weighing uses this principle with temperature-corrected water density and residual lung volume to derive body density and body fat percentage via the Siri or Brozek equations.
Age on Other Planets Calculator
Calculates your age on all 9 planets (Mercury through Neptune) plus the Moon and Pluto. Input: date of birth (for exact calculation) or age in Earth years. Optional weight input (kg or lb). Outputs for each body: age in planetary years, number of birthdays celebrated, countdown to next birthday (in Earth days/months/years), weight under that planet's gravity, and total sunrises witnessed (toggle). Planet data: orbital periods from NASA Planetary Fact Sheet; surface gravity ratios; sidereal rotation periods. Includes fun fact per planet. Earth summary shows total Earth years, days lived, and hours lived.