# Air Resistance!

1. Oct 23, 2005

### sharonita

So, here's the question:
The speed of falling rain is the same 10m above ground as it is just before it hits the ground. What does this tell you about whether or not rain encounters air resistance?

So here's my attempt:
Since the speed of the falling rain is just the same 10m above ground as it is right before it hits the ground, then the rain clearly does not encounter air resistance. Air resistance doesn't have as much, or any effect on compact objects. The rain is solely under the influence of gravity and the object is falling at a constant acceleration rate of 10m/s(squared) so therefore it will be the same at 10m above the ground, and just before ithits the ground.

any suggestions?

2. Oct 23, 2005

### Päällikkö

Ok, I will try not to help too much, to give you a chance to figure out the problem yourself.
F = ma.
I know it's very little help, but can you figure out how to apply the given equation (Newton II) in the problem?

3. Oct 23, 2005

### sharonita

mass x acceleration?
all im given is the acceleration. how do i apply the equation?

ps. thank you so much for your help!

4. Oct 23, 2005

### Päällikkö

If the rain drop has a constant velocity, it clearly encounters no acceleration. What then must the total force acting on the rain drop be? How can this be achieved?

5. Oct 23, 2005

### sharonita

Then the acceleration would be zero? If that is so then.. the force would be zero?

6. Oct 23, 2005

### Päällikkö

Exactly. If gravity does apply a force of magnitude mg to a rain drop, what does this tell you about air resistance?

7. Oct 23, 2005

### sharonita

I have absolutely no idea. Maybe it tells you that air resistance isnt noticable when the only force is gravity?

Bear with me =\

8. Oct 23, 2005

### Päällikkö

If the only force acting was gravity, F = ma = mg $\ne$ 0, the rain drop would have acceleration. It doesn't, though, if the velocity is to remain constant. So there must be another force acting too...

9. Oct 23, 2005

### sharonita

The air resistance is the force??

10. Oct 23, 2005

### Päällikkö

Yep.
Can you figure out its magnitude?

11. Oct 23, 2005

### sharonita

I honestly don't know how.
Whats the formula for that?

12. Oct 23, 2005

### Päällikkö

Again, if there's no acceleration (that is, the speed remains constant), the sum of forces must equal zero. There are two forces acting on the rain drop, the force of gravity and air resistance.

If you are having trouble with these basic consepts, I suggest reading your physics books, as it's explained better there.

EDIT: Physics really isn't about guessing the right formula. You actually need to combine many formulas in some problems, and to understand why and how, you need to understand the formula: what they say and where they can be derived from.

Last edited: Oct 23, 2005
13. Oct 23, 2005

### sharonita

Thanks so much!! Wow this forum is amazing&thanks so much for making me solve it myself. Not many people do that!!

14. Oct 23, 2005

### Päällikkö

No problem .

Well those the forum guidelines .