# How you put gravity in for the equation

1. Apr 20, 2006

### therealkellys

I realize this probably sounds like a simple question, but I was just wondering how you put gravity in for the equation. I know that gravity is equal to +/-(9.8 m/s^2). However, when you are putting it in an equation such a v=v0+at...do you use 9.8/(t^2) or just the rate...9.8? Thanks in advance for the help

2. Apr 20, 2006

### nrqed

You just put in 9.80 m/s^2 where "a" appears in the equation.

Actually, be careful about the sign. There are different conventions in the litterature.

Using a y axis pointing up, you may encounter $v_y= v_{y0} + a_y t$ in which case $a_y = -9.80 m /s^2$ or you may encounter $v_y= v_{y0} - g t$ in whcih case you use g = +9.80 m/s^2.

Patrick

3. Apr 20, 2006

### Pengwuino

Since acceleration is a vector quantity, it is always -9.8m/s