# Drag Force Equation?

## Homework Statement

Hi, i have a peculiar question after watching MIT lecture:http://ocw.mit.edu/courses/physics/...echanics-fall-1999/video-lectures/lecture-12/

What is the difference between the equation representing the drag force for a sphere: C(sub1)rv+C(sub2)r^(2)v^(2) and this drag force equation: (1/2)pv^(2)C(sub d)A

## The Attempt at a Solution

lightgrav
Homework Helper
viscous resistance is proportional to velocity (1st term), drag resistance is proportional to v² (2nd term).
at very slow speeds, the viscous term is larger ... at high speeds, the drag term dominates.

But why are there 2 different equation? Why didn't prof. WL just use the drag force one?

Sent from my iPhone using Physics Forums

haruspex
Homework Helper
Gold Member
But why are there 2 different equation? Why didn't prof. WL just use the drag force one?
It is very well explained in the lecture that C1rv+C2r2v2 is the general equation, but if you are in a regime where one of those terms is very much larger than the other then you can omit the smaller term. If that doesn't answer your question, please specify the section of the video (minutes from start) that's puzzling you.

I completely understand the lecture it's just that the equation represents the total resistive force on the object and I have a question on how is that equation(from the lecture) is different from the drag equation(google it) since they both shows the resistive force(if I'm correct)

haruspex