# Newton's First Law of Motion is Wrong (Proven Wrong in This Thread)

1. Mar 17, 2014

### NewtonWasWrong

First law: When viewed in an inertial reference frame, an object either remains at rest or moves at a constant velocity, unless acted upon by an external force.

Here is an experiment to prove this First Law wrong.
Consider two balls rolling at a constant velocity directly toward each other on a frictionless plane. Ball A is heading due east at 5 m/s and Ball B is heading due west at 5 m/s. The balls engage in an inelastic collision. The balls will both come to rest. This can be proven experimentally.

Please note that Newton's Second Law describes Force = Mass * Acceleration. Neither ball has an acceleration, meaning that neither ball has any force associated with it. So despite not being acted upon by any FORCE, during the collision, the balls change velocity from 5 meters/second to zero. This simple experiment clearly shows that an object will not necessarily stay in motion at a constant velocity despite not being acted upon by an external force.

2. Mar 17, 2014

### Staff: Mentor

This is silly. When the balls collide they exert forces on each other!

3. Mar 17, 2014

### NewtonWasWrong

Please note Newton's Second Law of Motion:

Second law: The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object; thus, F = ma.

Please note that the acceleration of both balls are equal to 0. Please note that mass*0=0. Consequently, neither ball produces a force (or rather, produces a force equal to 0).

4. Mar 17, 2014

### Staff: Mentor

Only before they collide! Once they collide, they certainly have a non-zero acceleration. You indicated such yourself!

5. Mar 17, 2014

### Staff: Mentor

In the collision, both balls change their speed from five meters/second to zero meters per second. That's an acceleration, and you can even calculate its average value throughout the collision: If the time between when the balls first touch andwhen they stop moving is $\Delta{t}$ seconds, the average magnitude of the acceleration will be $\frac{\Delta{v}}{\Delta{t}} = \frac{5}{\Delta{t}} m/sec^2$.

Non-zero $a$, non-zero $m$, gotta be a non-zero $F$.

6. Mar 17, 2014

### Staff: Mentor

Next time, before posting an obviously wrong and completely ignorant challenge to an established theory it might be good to exercise a little humility and actually learn enough of the theory to be able to use it correctly.

You completely failed to recognize the obvious forces acting on the objects, and therefore completely failed to correctly apply the theory. Furthermore, you arrogantly assumed that you were the only person in the last 300 years smart enough to have correctly analyzed an inelastic collision using the theory.