Originally Posted by compressor stall
Quote:
Neither does gravity, for that matter - if a feather were as aerodynamic as a bomb, they would both fall at the same speed.
So you have two bomb shaped objects of identical shape. One is made of graphene and filled with feather fibres (ie really light) the other normal alloys and explody-bits in the middle.
Both are dropped from a B1. Which hits the ground first?
I apologise for oversimplifying.
Ballistic Coefficient is the ratio of sectional density to coefficient (aerodynamic) form. It's effectively a combination of streamlining and inertia, which are both used to overcome the forces of wind resistance (friction). The reason a feather and a bowling ball both fall at the same rate in a vacuum is because gravity is a constant in relation to the earth's mass (9.8ms/s) acting on all atoms (regardless of mass):
https://web.stanford.edu/dept/news/p...ity990825.html
Once wind resistance (friction) enters the fray, then something is needed to overcome that resistance for an object to continually accelerate at 9.8ms/s - an equal force to the opposing wind resistance.
A body in motion will not alter its course unless acted upon by an external force.
The body in motion has kinetic energy - 1/2 mass x velocity squared. Therefore, a proportional force is needed to slow its acceleration from 9.8 ms/s. That force increases as the kinetic energy of the object increases. However, the forces of wind resistance (friction) increase with air density (more atoms per equal volume = great frictional force) and the surface area of the moving object they are acting on. The square-cube law dictates that volume - and all other things being equal, mass - increases faster than surface area. So if two moving objects have the same density and form (both spherical, for example), the larger object will have more kinetic energy in relation to wind resistance. The same equation can be applied to two moving objects of the same form but different densities (mass/volume).
That answers your question as to why greater density of equal form can overcome the frictional forces of wind resistance when accelerated by the same force (gravity).
My question is, if two objects - regardless of size and mass - are moving within a constant air mass, and are not subject to wind resistance or any other physical force within that air mass, what force will cause those objects to alter their velocity?