# Acceleration down a frictionless ramp- what does a y represen in this case?

1. Sep 15, 2009

### Kalibasa

Acceleration down a frictionless ramp- what does ay represen in this case?

I wish I could upload a picture or something, but I don't have a scanner! I'm looking at an object moving down a frictionless ramp; the main acceleration vector points straight down, ax of course is parallel to the ramp, and ay is pointing back "into" the ramp at an angle. It seems like ax here takes the place of a in other problems (it's the acceleration vector that actually tells you how the object is moving through space). Is this right? But then I don't understand what ay is in this case! If on a normal axis ay tells you how fast the object is accelerating in a vertical direction, what does it actually mean in this case? How can an object accelerate, even in part, back into a ramp?

I'm seriously confused! Thanks :)

(PS Sorry if this is in the wrong forum, but I'm not really doing homework, I'm just trying to understand the concept... let me know if I should have posted elsewhere)

2. Sep 17, 2009

### turin

Re: Acceleration down a frictionless ramp- what does ay represen in this c

You're right to be confused. A force vector can point into the ramp, but not an acceleration vector. The motion is constrained. Acceleration is a property of motion, and is the result of forces. Perhaps the acceleration is the "acceleration of gravity", which is not actually an acceleration. The acceleration of gravity is what the acceleration of the object would be if it were unconstrained.