Weigh the impacting object on your mass scale. Be sure you are measuring in kilograms.
Determine the impact velocity of the object. If the object is falling to the ground, its impact velocity will be equal to the square root of the product of the height of its fall multiplied by 19.6 (two times the acceleration due to gravity). If the object in question is a projectile, the impact velocity will be equal to its launch velocity.
Square the result calculated in Step 2, and multiply it by one-half of the value of the mass measured in Step 1 to determine the object's kinetic energy.
Divide the kinetic energy calculated in Step 3 by the distance traveled by the object after the point of impact to determine the impact force of the object in Joules.