Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: The sign of g



I usually say something like this:

"We will learn later that an acceleration is always due
to a net force acting on an object. Keep this in mind. In
this case the force of gravity is causing g; it is directed
down. If you decide to make 'up' positive then the
'down' must be negative, and vice versa."
Ludwik Kowalski

Tina Fanetti wrote:

I know we have discussed this before I think, and I read about it in
Aarons..

How do I explain to a student that when we choose up (+y) to be
increasing, we say that the sign of g is negative, regardless of
whether the ball is going up or going down.

My students seem to get that when the object is going up, g is
negative. They want to make the ball going down positive g.
But it stays negative because of the choice of axis.

I am at a loss because until I read Aarons I thought that it
changed signs too...