The net force F on a body is proportional to the acceleration a(t) of the body, where m denotes the mass of the body as the constant of proportionality.
F1 is the force exerted by the first body (on another body) (N)
F2 is the force exerted by the second body (on another body) (N)
Notes
Every action has an equal and opposite reaction. In other words, the force F1 exerted on the second rigid body by the first is equal in magnitude and in the opposite direction to the force F2 exerted on the first rigid body by the second.
|d| is the Euclidean norm of the distance between the center of mass of two bodies (m)
ˆd is the unit vector directed from the center of the large mass to the center of the smaller mass (m)
d is the distance between the center of mass of the rigid bodies (m)
Notes
Two rigid bodies in the universe attract each other with a force F that is directly proportional to the product of their masses, m1 and m2, and inversely proportional to the squared distance |d|2 between them.
The net torque τ on a rigid body is proportional to its angular acceleration α, where I denotes the moment of inertia of the rigid body as the constant of proportionality.
We also assume that all rigid bodies involved are two-dimensional (from A:objectDimension).