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.xphysics said:But why are there 2 different equation? Why didn't prof. WL just use the drag force one?
Perhaps you're not reading the fine print. E.g. http://en.wikipedia.org/wiki/Drag_equation:xphysics said: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)
http://en.wikipedia.org/wiki/Drag_%28physics%29:The formula is accurate only under certain conditions: the objects must have a blunt form factor and the fluid must have a large enough Reynolds number to produce turbulence behind the object.
where the Reynolds number depends on the speed (linearly). I.e. the linear term of the full equation has been hidden inside the drag coefficient.The drag coefficient depends on the shape of the object and on the Reynolds number:
At low Reynolds number, the drag coefficient is asymptotically proportional to the inverse of the Reynolds number, which means that the drag is proportional to the speed.
The drag force equation is a mathematical formula that calculates the force of air resistance on an object moving through a fluid, such as air. It is a function of the fluid density, the velocity of the object, the object's cross-sectional area, and the drag coefficient.
For spheres, the drag force equation is simplified to Fd = 1/2pv2CdA, where Fd is the drag force, p is the fluid density, v is the velocity, Cd is the drag coefficient, and A is the cross-sectional area of the sphere. This equation is used to calculate the drag force on a spherical object moving through a fluid.
The drag force equation is the same for all objects, but the values for the variables may differ depending on the shape and characteristics of the object. For example, a streamlined object will have a different drag coefficient than a rough, irregular object.
The drag coefficient, denoted as Cd, is a dimensionless quantity that represents the amount of drag experienced by an object. It takes into account the shape, size, and surface characteristics of the object. A lower drag coefficient means that the object experiences less drag, while a higher drag coefficient means that the object experiences more drag.
The velocity of an object has a significant impact on the drag force experienced by the object. As the velocity increases, the drag force also increases. This is because at higher velocities, there is a larger amount of fluid passing over the object, resulting in a greater force of air resistance. This relationship is represented by the squared term in the drag force equation.