Drag force is the resistance of a fluid, the force that it applies acting opposite to the motion of an object that is moving submerge in a certain fluid.
Drag = (density) * (square of the velocity) * (Drag coefficient) *(transversal area)
The equation is written FD = ½ ρ * v2 * CD * A
We have: FD: Drag force
ρ: fluid density
v: Relative velocity between the fluid and the object
CD: Drag coefficient
A: Transversal area or cross-sectional area Drag Formula Questions:
1) A car travels with the speed of 90 km/h have a drag coefficient of 0.32.
a. FD = ½ (1.2 Kg/m3)*(25 m/s)2 * 0.?? * ? m2 = 600 Kg*m/s2 =600 N
If the area of cross-section is 5 m2, what is the drag force? The air density is 1.2 Kg/m3.
2) what is the drag coefficient of an object moving in water and that feels a drag force of 500 N?
The sectional area is 2 m2 and is moving at 30 m/s. From the formula of drag we, can find the drag coefficient,
a. CD = 2 * FD / (? * v2 * ?) Substituting the values in the formula above, with the density of the water 1 Kg/L,
CD = 2 * 500 N / (1 Kg/L * (30 m/s)2 * 2 m2)=
CD = 2 * 500 N / (1000 Kg/m3 * (30 m/s)2 * 2 m2)= 0.00055