Currently in my investigation I am trying to find the relationship between crater diameter and the kinetic energy of the ball bearing Iím dropping (changing the kinetic energy by dropping it from a greater height). I found a theory online that explains the relationship that should be seen but I am confusing about one part of it.
Anyway here is the theory behind it. I will underline and bold the part that confused me:
The last statement, about the scaling for any shaped crater, is the one that has me. How can this theory be true for any shape with any scaling factor? As most craters are spherical I donít know how this above theory can be applied to that?
Here is an approach you may find helpful:- the formation of a crater is akin to digging a hole.
To start with let us consider the minimum potential energy change that occurs when a cubic hole, side-length s, is created in sand.
This will be the same as lifting a similar-sized amount of material onto nearby ground.
D = length of one side of the cube
d = density of the impact material
m = mass of sand
Volume of hole = D^3 where D is the length of one side of the cube
Mass of material moved from hole
Mass = volume x density = D^3 * d
Weight of this material = mass * Acceleration due to gravity
Weight = g * D^3 * d
Potential energy gained = weight x height lifted; as the height lifted is equal to the length of one side of the cube so this is height through which the mass must be lifted:
E = g * D^3 * d * D
E = g * D^4 * d
As the density and the acceleration due to gravity are constants this can be re written as
E = kD^4 where k is a constant.
This will be true as the scaling factor for any shape of crater.
This is a math question as it is not the physics that confuses me but rather the mathematics.