I know that if you are accelerating upward in an elevator, you will have more weight (if you are on a scale) due to normal force of the elevator pressing up into you? Would that happen if you are currently moving downward and (negative velocity) if you accelerate upward? Would that change the effect of acceleration on your weight?
[Physics] Does the velocity you travel affect your weight in an elevator
accelerationgravitynewtonian-mechanicsvelocityweight
Related Solutions
Just don't start writing equations without a complete Free-Body-Diagram(may be rough diagram) according to the frame of reference..
1)Ground Frame
Now . Newtons law. $$\sum \vec{F_{ext}}=\frac{dp}{dt}=ma(for\ constant \ mass)$$
So, $$N-mg=\sum \vec{F_{ext}}=ma$$ Where system is boy in ground's frame.
Here we equate the net external force to the acceleration of body . $ma$ is not a force it is the measure of net force which causes body to accelerate.
2)In a accelerating frame(non-inertial)
here we have to add a fictious force $-m\vec{a}$ where $\vec a$ is the acceleration of frame .
Here too $$N-mg-ma=\sum \vec{F_{ext}}=0(as \ in \ frame \ of \ elevator \ boy \ is \ at \ rest)$$ Again you get $$N-mg=ma$$
As you said correctly: as you accelerate upwards, the normal force acting on you will increase. Now look at the situation from the scale's "perspective" -- consider the forces acting on the scale:
Since the ground (i.e. the scale on which you stand) applies a normal force $F_N$ (upwards) on you, Newton's 3rd law says that you must also be applying a force $F_N$ (downwards) on the scale.
To summarize: the scale will measure the magnitude of the normal force acting on you; which is also the magnitude of the force you exert on the scale (by Newton's 3rd law).
Best Answer
you are moving currently downward,but your speed is decreasing ,that would mean you are accelerating upward. In that case also your apparent weight will be given by,
$n=m(g+a)$ ,where $m$ and $a$ are mass of you and acceleration of the elevator respectively. Only acceleration matters not your current velocity ,this is a consequence of Newton's laws.