Change a world. See what gravity does.

The source uses a spherical Newtonian model. Surface gravity equals G times body mass divided by radius squared. Hold body mass at the Earth preset, five point nine seven two times ten to the twenty four kilograms. Start with radius six thousand three hundred seventy one kilometers. The input marker is at one reference radius. Gravity is about nine point eight two meters per second squared. The output marker lies on the same formula curve. Radius must be converted to meters before squaring. Now increase radius while leaving body mass fixed. The top marker tracks the radius input, from one to two reference radii. The lower marker follows the inverse square curve. Its horizontal position uses that same radius ratio, and its vertical position uses the acceleration actually calculated from that radius. The falling value is a mathematical comparison of spherical bodies, not an actual transformation of Earth. Hold the radius at twelve thousand seven hundred forty two kilometers, twice its initial value. Gravity is now about two point four five meters per second squared, exactly one quarter of the initial acceleration within this model. The markers stop while we read that result. Doubling body mass at a fixed radius would instead double gravity; that is a separate comparison. These formulas ignore density changes and general relativistic corrections. Keep the original Earth mass and radius fixed, so surface gravity stays about nine point eight two meters per second squared. Object mass is a separate input. Start with seventy kilograms. Weight equals object mass times surface gravity, so the initial weight is about six hundred eighty seven point four newtons. The upper marker shows object mass and the lower marker shows the weight on a straight line through the origin. Mass is measured in kilograms; weight is a force in newtons. Increase only the object mass from seventy to one hundred forty kilograms. The shared horizontal coordinate follows the mass input. The lower marker rises by the exact weight formula at each intermediate mass. Changing this input does not alter the body mass, radius or calculated surface gravity. The straight line makes the proportional relationship visible; it is not a decorative reveal of a fixed answer. Hold the object mass at one hundred forty kilograms. Weight is now about one thousand three hundred seventy four point eight newtons, twice the initial weight. The markers remain still while that number is spoken. The calculator accepts positive body mass, radius and object mass, and nonnegative orbital altitude. Invalid inputs retain the last valid stored result. Presets, calculation, reset and local saved state remain available in the tool above. Circular orbital speed equals the square root of G M divided by R plus altitude. Hold Earth body mass and radius fixed. Start at the source default altitude, four hundred kilometers. The circular speed is about seven point six seven two kilometers per second. Surface escape speed is about eleven point one eight six kilometers per second. The horizontal reference line shows that surface escape value. It stays fixed because changing orbital altitude does not change the surface radius in this calculator. Increase only orbital altitude from four hundred to four thousand kilometers. The upper marker tracks altitude, and the lower marker moves along the exact circular speed curve. More altitude means a larger distance from the center, so the circular speed decreases. This animation compares circular orbit conditions; it does not simulate a spacecraft accelerating or climbing between those orbits. Hold altitude at four thousand kilometers. Circular speed is now about six point one nine nine kilometers per second, while surface escape remains about eleven point one eight six. These two speeds are evaluated at different radii. The square root of two escape to circular speed ratio applies only when both are evaluated at the same radius. The tool ignores drag, spin, propulsion and relativity. Download Gravity Brief exports its actual inputs and computed values as text; the download control remains above this video.