# When is work done?

1. Apr 9, 2010

### pconstantino

Hello.

If a particle has some P.E. say 100J, when we release it, considering theres air resistance, will gravity do more work than if there was no air resistance?

Thanks

2. Apr 9, 2010

### Staff: Mentor

What do YOU think? What factors come into play when there's air resistance? And does gravity do work on more than just the particle when there's air resistance?

3. Apr 9, 2010

### pconstantino

i think gavity does 9.8 * distance of work, and air resistance does -X * distance of work, which at the end decreases the total energy of the particle, is that right?

4. Apr 9, 2010

### SpectraCat

Heh ... my work is *never* done. :tongue:

5. Apr 9, 2010

### pconstantino

oh come on... let me go back to my books then.

6. Apr 9, 2010

### nonequilibrium

Yup, if the distance doesn't change, the work done by gravity is the same (you did forget the factor m). The fact that the drag makes the total work done over a certain distance less was to be expected, as the mechanical energy (potential + kinetic) is known to decrease in the presence of friction.

7. Apr 9, 2010

### pconstantino

omg i forgot the mass lol, sorry. thanks mr vodka :P

8. Apr 9, 2010

### peeyush_ali

how is the force due to air resistance acting?? (like in general proportional to displacement or velocity of the particle (instantaneous)) and yes..is the collision between the particle and the air molecules is inelastic?? if so then the mass of the aprticle is increased in due course of time...??
hm.., but in general if u wud like answer the question then, the answer is "yes" for same distances in 2 cases ie., ( i) with air friction..2)without air friction)