Thread: Why does v represent speed in the KE Equation?

I was reading some physics stuff today, and I saw that in the Kinetic Energy Equation (KE = 0.5mv^2), v is used, but v represents speed instead of velocity. I understand why Kinetic Energy is related to speed and not merely velocity, but why is v used to represent it? v represents velocity in many other equations. It seems really screwed up because there is already common confusion about the difference between speed and velocity. Also, is there any other symbol for speed itself in physics? I know that c represents the speed of light, but I am talking about just general speed.

I looked at a bunch of web sites, and lots of them said that v represents velocity. That doesn't seem to make sense because total distance and not merely distance in a given direction would be what counts for energy usage. If something zigzags at a certain speed in a given direction, it uses more energy than it does if it moves at the same speed in a straight line for the same distance in the given direction. So it seems.

Thanks.

You'd need to know in advance that the Kinetic Energy and Work equations are scalars. Anyways, I drew this to demonstrate that KE can still be written in terms of velocity (and not speed) v.

Because a vector to the second power yields a scalar, so it doesn't matter if you use speed or a velocity. And v is a common symbol.

My God, now I know how this guy feels.



Okay, I sort of see what you are saying, but I need to learn about several things before I fully understand it. You two seem a few hundred miles ahead of me on this stuff. Thanks for your efforts.

So KE = 0.5(mv^2) where v represents velocity is a legitimate form of the Kinetic Energy Equation? I'm pretty sure that's what you are saying. It has something to do with several sub-velocities taken into account? It is very clear to me why the equation would work for an object moving in a straight line. It's just when curved paths and so forth come into it that I don't totally see how it's possible.

What other symbol can be used to represent speed?

Your equation is incomplete

KE = (mc^2 / (sqrt(1 - (v^2/c^2))) - mc^2


And usually if you want to represent speed in an equation you would use ds/dt or |v|. |v| is more common.

*Why doesn't DV support special characters anymore? Those d's should be deltas.

Originally Posted by ninja9578

Your equation is incomplete

KE = (mc^2 / (sqrt(1 - (v^2/c^2))) - mc^2

WTF?

http://www.google.com/#hl=en&source=...96bd6416f4afd8

Also, c represents specifically the speed of light.

Originally Posted by ninja9578

And usually if you want to represent speed in an equation you would use ds/dt or |v|. |v| is more common.

Absolute value of velocity? That's not necessarily speed.

I am talking about just a single variable.