Drag, Lift and Terminal Speed
Drag in relation to velocity
\[D\propto v^2\]
What 3 things affect drag?
- Surface area
- Velocity
- Density of the fluid you are going though
A skydiver is falling towards the earth at a terminal velocity of \(45ms^{-1}\). Describe what she could do to change her terminal velocity.
- The skydiver could increase her surface area by spreading her arms out. This would increase the air resistance on her and increase the drag force overall.
A rubber ball of mass 0.120kg is dropped from a tall building. Calculate the magnitude of the drag force as it falls through the air at it's terminal velocity.
- \(F=ma\)
- \(F=0.120 \times 9.81=1.1772N\) of force going downwards.
- At terminal velocity, the upwards force = the downwards force, therefore the drag = \(1.1772N\).
At \(10ms^{-1}\), the drag force acting on a car is 1.0kN. What is the drag force acting on the same car travelling at \(30ms^{-1}\)?
- \(9.0kN\)
Determine the instantaneous acceleration of each object.
- Skydiver with 800N downwards and 300N upwards.
- \(F=ma\)
- \(\frac{800}{9.81}=81.5kg\)