# Calculating equatorial velocity

1. Mar 12, 2010

### awygle

I'm confused about some results I've been getting. I tried calculating the equatorial velocity of Earth by the equation $$R\varpi=v$$, and I got ~465 $$m/s$$. According to various resources, this is correct. But then I tried to calculate it again, using $$g=a_{c}=\frac{v^{2}}{R}$$, and I got ~8000 $$m/s$$.

Obviously, the second is wrong. My question is why? My only guess is that maybe g doesn't work as $$a_{c}$$ in this case due to the normal force from the Earth or something of the sort, but that seems a weak explanation...

2. Mar 12, 2010

### Stonebridge

It's wrong because the equation is not the correct one to use.
You have calculated the speed an object would have to travel in orbit around the Earth if its path was literally just above the surface. In other words, its centripetal force was provided by its weight.

3. Mar 12, 2010

### SAINATHAN

earth has both rectilinear and rotatory motion.but you take a=v^2/r.so your assumption is wrong.

4. Mar 15, 2010

### SAINATHAN

hi,friend in your equation how we have take a=g.that is for surface on earth and although 'g' is not constant at all.