Re: Do you have to counteract 1 pound of mass with one pound of thrust

Nick,

When we're talking about forces, we usually choose a direction for a force 
to have a positive direction and a negative direction. For our one-pound 
body, we'll say the direction toward the ground is negative and the 
direction upward is positive.

When we measure that one pound of weight for the object, the direction of 
the force is toward the ground, so it's negative one pound. 

When we apply one pound of thrust against the object's weight, we're 
pushing upward, so that push is positive one pound of force.

If we add the two forces together, we get

1 + (-1) = 0

The two forces exactly cancel one another, and our one-pound object won't 
go anywhere at all!  There has to be a net positive force for the object to 
accelerate upwards: in a one-gravity field, we have to actually apply two 
pounds of force to make the object accelerate at one gravity upwards.

Things are a little different if there is no gravitational force acting on 
the body.

If we go out to a place where gravity isn't acting on anything, then the 
object will not have a weight force pulling on it. If we apply one pound of 
force to it, then it will accelerate at thirty-two feet per second per 
second because the force we're pushing with is the only one acting on the 
body.

I hope this is helpful.