# B Air Resistance

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1. Mar 19, 2017

### MarcusK

If air resistance increases with velocity, then if a ball is thrown upwards, does air resistance decrease as the upward velocity of the ball decreases or does it only increase and remains constant when the upward velocity of the ball decreases?

2. Mar 19, 2017

### PeroK

What do you think? And why?

3. Mar 19, 2017

### rahaverhma

Not getting clear in your last line.

4. Mar 19, 2017

### MarcusK

it's in the question: I think that "air resistance could decrease as the upward velocity of the ball decreases or it could increase and then remain constant even when the upward velocity of the ball decreases" Air resistance could decrease because it is strictly dependent on air resistance, i.e. air resistance opposes motion, therefore increasing when the object has a velocity or is accelerating. Or Air resistance could increase right after the ball leaves the hand of the person who threw the ball, and remain constant at that amount of opposing force even if the object begins to decelerate due to gravity.

5. Mar 19, 2017

### rahaverhma

Before the release, we might have been applying the force but just after the release we are not applying any force, the ball has inherited the motion of the hands, and it is having its own velocity.
Now why to take the gravity, to know about the behavior we should go special instead of going through complicated situations.
So, after initial velocity, the air resists it let for 'dt' time, then its velocity decreases, now in again another 'dt' time it encounters with less no. Of air particles which can be calculated by the product of its velocity at that instant and dt time.
This way we conclude to the formulae

M. (dv/dt) = - k. v = - k. (ds/dt)
Where k depends on quality of air., density of air.

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