Constant Velocity 'Force'? According to Newton's second law, $F = ma$. If acceleration is zero then the force must be zero, but assuming you have an object moving with a constant velocity of say $2 \mathrm{ms^{-1}}$, and that object strikes you, then obviously some sort of 'force' would be felt by you, so my question is what do you call that 'force' since it actually is not a 'force' and is there an equation to calculate it?
 A: Some students learning physics for the first time mistakenly think that objects that are accelerating have force.
Force is not a property possessed by an object, but rather something you do to an object that results in the object accelerating (changing its speed), given by the equation F = ma.
That is, Forces cause acceleration, not the other way around.  This means that if you observe an object accelerating, then it implies a force is acting on the object to cause such an acceleration.
In this case, as the object strikes the hand, your hand applies a force to the ball causing it to slow down (decelerate), and the ball applies an equal and opposite force to your hand causing it to accelerate ever so slightly (Newton's third law), which is detected by your sensory neurons.
A: When two objects (of mass $m_1$ and $m_2$) collide with relative speed $v_{rel}$ then there is an exchange of momentum (called an impulse) of magnitude
  $$ J = \frac{(\epsilon+1)\,v_{rel}}{\frac{1}{m_1}+\frac{1}{m_2}} $$
where $\epsilon$ is the coefficient of restitution and it describes if the objects bounce or stick.
This impulse changes the speed of the object by $\Delta v_1 = -\frac{J}{m_1}$ and $\Delta v_2 = \frac{J}{m_2}$.
The actual force cannot be found from this as it changes rapidly with time, but an average force can be computed if you know that the impact takes $\Delta t$ time to occur.
$$F_{average} = \frac{J}{\Delta t} $$
PS. The definition of the impulse is $J = \int F(t)\,{\rm d}t$. 
A: When an object, moving at a constant velocity, hits something, it will either stop, decelerate (or accelerate in some cases), or bounce back. During this collision time, there is a change in velocity (acceleration/deceleration) of the moving object, hence force is exerted on the wall (or in this case, on you), due to change in velocity. Hence we can use Isaac Newton's 2nd Law:
 $$ F= ma = m(dv/dt) = m(d^2x/dt^2)$$
A: Assume a ball 0.1 kg hits a wall with a speed of 2 m/s and bouce back in 0.2 sec, deceleration will be 2/0.2=10 m/sqsec, and force will be 1.0 N.
A: Resistance or reaction that stopped a striking object is a (d'Alembert's) force that causes you pain on impact deceleration ( high velocity reduced to zero in a small distance) $ =v^2/( 2 s).$
