Gravitation Lab

Everywhere

• Topic tabs (under the title) switch between simulations in this lab. Some topics have smaller buttons under the stage for their screens.
• Teach shows live equations with the current numbers and "What to notice" points. Practice gives a numeric problem and a quiz.
• Move the sliders or tap the chips in the right-hand panel. The readings box updates live.
• Pause / Restart control the animation. Clean view hides everything except the stage, for projecting or recording; press Esc to leave it.
• In Practice, type a number (e.g. 12.5 or 3.2e-10), press Check or Enter. Show it on the stage sets the simulation to that problem.
• Nothing is saved: scores reset when the page is reloaded.

Language

• Choose English or বাংলা once on the home page (top right); every lab then opens in that language — tabs, controls, readings, equations, notes, problems and quizzes.

Newton's law

• Two masses: two people, an apple and the Earth, the Earth and the Moon, or the Earth and the Sun; change the separation and watch the inverse-square graph.
• Field round a planet: field lines, g = GM/r² at any distance, and g at the surface of the Moon, Mars, Earth and Jupiter.

Variation of g

• With height: the exact gR²/(R + h)² against the approximation g(1 − 2h/R), up to 20 000 km.
• With depth: only the sphere below you pulls; g ∝ r inside, 1/r² outside.
• With latitude: the spinning Earth, the centripetal term ω²R cos²λ, and the measured curve from 9.78 to 9.83 m/s².

Potential & escape

• Potential well: V = −GM/r, the energy of a chosen mass, and the work to climb out.
• Escape velocity: throw something straight up from Earth, Moon, Mars or Jupiter at any speed; it either falls back or escapes, with the KE / PE / total-energy bars beside it.

Satellites

• Circular orbit: set the height; v = √(GM/r), T = 2π√(r³/GM), the energies, and the v–h and T–h graphs with the 24 h line marked.
• Geostationary: the Earth turns, the geostationary satellite turns with it over Dhaka, and a low satellite laps them both.
• Weightlessness: a person on a scale in a lift; N = m(g + a), down to the free-fall case a = −g that a satellite lives in.

Kepler's laws

• 1st law: an ellipse with the Sun at a focus, eccentricity from 0 to 0.85, with the speed varying correctly along the orbit.
• 2nd law: two slices swept in equal times, with their areas worked out to show they are equal.
• 3rd law: the eight planets on a log–log plot of T against a, slope 3/2, and T²/a³ for each.

Full guide with teaching tips: User manual (also as a PDF).