The law of universal gravitation $F = G\dfrac{m_1 m_2}{r^2}$, the force of gravity $F = mg$, weight and weightlessness.
| Symbol | Name | Unit |
|---|---|---|
| magnitude of the force of attraction | N | |
| gravitational constant | N·m²/kg² | |
| mass of the first body | kg | |
| mass of the second body | kg | |
| distance between the bodies (between centres) | m |
Note. Valid for point masses and for spherical bodies (the distance is between the centres). . Twice the distance gives a force 4 times smaller. For example, two bodies of each, apart: .
| Symbol | Name | Unit |
|---|---|---|
| magnitude of the force of gravity | N | |
| mass of the body | kg | |
| acceleration of free fall | m/s² |
Note. Near the Earth's surface ; in problems is often used. On the Moon , on Mars . For example, a 2 kg body on Earth (): .
| Symbol | Name | Unit |
|---|---|---|
| weight of the body | N | |
| mass of the body | kg | |
| acceleration of free fall | m/s² |
Note. Valid if the body is at rest (or moves uniformly) on a horizontal support or hangs from a suspension. Weight acts on the support or suspension, the force of gravity acts on the body; they are equal in magnitude. In free fall (weightlessness).
Set the quantities with the sliders. The graphs and the formulas with your numbers update at once.
The bodies attract each other with forces equal in magnitude (Newton's third law). r is the distance between the centres; the bodies are drawn schematically.
The force is in millinewtons: 1 mN = 0.001 N. Click the graph to set the distance.
The mass of the body is the same on every planet, while the force of gravity (and the weight of a body at rest) is proportional to g. The g values are rounded table values.