what causes the drag force?

Question

please include ideas about particles in your answers

Answer 1

D = 1/2 rho Cd A v^2; where D is drag force, rho is air density, Cd is the coefficient of drag, A is the cross sectional area, and v is the velocity relative to the moving object.

The air density is of course a measure of how many air molecules (the particles) there are per volume. Thus, you can see that when everything else is the same, the drag goes up relative to the air density or number of particles per unit volume. That is, drag is proportional to the number of particles per volume the moving object runs into at velocity v.

Cd is a fixed coefficient for each specific object. It is usually found experimentally because the factors that go into its value are too complex to derive the coefficient. A is just the area perpendicular to the direction the object is going. A is easy to find; for example, A = pi R^2 for a sphere with radius R.

Of interest is that D ~ v^2, which means doubling the velocity over the object will quadruple the drag acting on it. And this means, if the object is to continue going forward with a constant acceleration, the thrust has to quadruple as the velocity accelerates to twice what it was.

Answer 2

Drag force is caused by particles temporarily bonding at the surfaces. This is most apparent when looking at drag between sliding metal plates. It is also caused by the momentum of particles hitting into the other object's particles when talking about, for example, a parachute dropping from altitude. The parachute encloses more particles than can escape, and so the velocity of the falling parachute decreases in proportion.

Answer 3

First tell me why you're angry?!(just kidding!)
see sweetie,you know that the molocules of a substance are attached to eachother by some forces like the hyrogenic or ionic or coalanci(i'm not sure the dictation is right) and these forces cause the drag force of a stuff.for example when the surface of a plate is greecy,if u pure some water on it,they will take the shape of drops and it's because that the surface drag force between water molocules is more stronger that the one between water and the greecy plate so they become like drops.Another example,u've seen that when there's some water in a glass,it's surface is concave,it's also because that the beneath molocules,drag the molocules on the surface toward themselves and this force in stronger in between,so the surface become cocave.

Answer 4

Drag on an airplane is caused by mometum transfer of particles hitting the surfaces. Also, drag is caused by boundary layers and their resistance to slipping.

Answer 5

In an airplane, it's usually turbulence produced by the airframe, which is why the right airframe design is important. Wind tunnel tests reveal areas of high turbulence to be eliminated.

Answer 6

friction