Aclock on a moving train runs an identical clock at rest.

It depends who is watching it.

-- A passenger on the train says that his clock is normal, but the clock at the station he just passed is running slow.

-- A ticket agent at the station says that his clock is normal, but the clock on the train that just rolled through is running slow.

-- They're both correct, but ...

-- The difference is too small for either of them to notice, unless the train is going faster than about half the speed of light.

-- It isn't.

your answer is, orbit around the nucleus

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.