An object's motion is affected by the initial speed and
acceleration and the forces that interact with it, the most
important being:
Gravity - that is affected by the gravitational constant g - which
is affected by altitude;
Air friction - that depends on the speed of the object and it's
volume and air density;
Surface friction - depends on the size of the surface of contact,
the force that the object exerts on the surface, the surface and
the object's coefficient of friction;
All the above forces are proportional to the mass of the object.
Acceleration aka Force, and Mass
