# What is a velacity?

1. Jul 3, 2009

### lola.bonane

What is a velacity? I am so confused. Further what is a acceleration?

I tried to read the wikipedia article on position, but it didn't make sense.

"A position, location or radius vector is a vector which represents the position of an object in space in relation to an arbitrary reference point."

I don't even know what half of these terms mean.

Help appreciated :)

2. Jul 3, 2009

### Danger

Re: Velacity

Welcome to PF, Lola.
In the simplest terms, velocity is a vector rather than scalar measurement. It describes both the speed and the direction of travel. For instance, 30 miles-per-hour is a speed. 30 miles-per-hour east is a velocity.
Acceleration is a change of velocity. That can mean that the speed changes, or the direction, or both.

3. Jul 3, 2009

### lola.bonane

Re: Velacity

"In the simplest terms, velocity is a vector rather than scalar measurement. It describes both the speed and the direction of travel. For instance, 30 miles-per-hour is a speed. 30 miles-per-hour east is a velocity."

I dont understand what vecotor means because it is so hard to understand. Can you please explain? thanks.

also, my professor has been talking about - and + aceleration, but i dont get the difference. what do these mean?

4. Jul 3, 2009

### negitron

Re: Velacity

I think you mean velocity. A velocity is a vector quantity representing the speed of an object--the vector part means that direction is a component, as well. An acceleration is merely the rate of change of a velocity. The important concept here--which is difficult to grasp at first--is that an object can undergo acceleration without changing speed; since direction is a component of the velocity vector, changing direction also results in acceleration. In physics, both an increase or a decrease in velocity is called acceleration.

5. Jul 4, 2009

### lola.bonane

Re: Velacity

okay thanks so much for your guys help but i just dont understnad what is a speed and what is a velocity.

"since direction is a component of the velocity vector"

whoa whoa whoa back up the truck there. what is a component and how does that even mean velocity?

6. Jul 4, 2009

### negitron

Re: Velacity

Think of a vector as a picture of an arrow. The way the arrow is pointing represents the direction and the length of the arrow represents the magnitude (in this case, the speed). Component is simply a term which means "a part of."

7. Jul 4, 2009

### Danger

Re: Velacity

May I ask you, Lola, if English is not your mother-tongue? If it's a second language for you, we will take a different approach to explaining things.

8. Jul 4, 2009

### Kaimyn

Re: Velacity

Think of it this way. Speed is absolute. No matter what direction you are going in, you are going at 30km/h. There is no negative speed. Velocity, on the other hand, can have a direction as well as a speed.

A simple way to look at it is this. Imagine a cartesian plane. Every integer along the x-axis is another metre. Now, say there is a point moving along the x-axis, one integer per second. In this example, it makes it 1m/s. To say that as each second passes, the number under the point is getting bigger by one metre would be the same as saying that it has a speed of 1m/s, and a velocity of 1m/s. But now imagine that the point moves such that it gets smaller by one metre every second. It's speed is still 1m/s, but it's velocity is now -1m/s. In summary, speed is just how fast something is going, where as velocity shows the direction as well. You should note that the point would be moving continously, that is, it doesn't stop (i.e. after half a second it will have moved half a metre).

Now acceleration is the change in the velocity, just as velocity is the change in position*. We write this as m/s/s or m/s2. Imagaine again the point we taked about in velocity. Imagine, in the first second, it moves one metre. In the second second, however, it moves two metres. In the third second, it moves three metres and so on. If this is the case, it is accelerating. In this case, it is accelerating at 1m/s2. A negative accelaration doesn't mean that the point is moving backwards, rather it means it is slowing down, just as positive acceleration is speeding up. So if the point is moving at 6m/s, and deccelerates at 1m/s/s, after the first second it will be going 5m/s, the second 4m/s and so on.

Sorry if you don't understand metres. If you don't, just replace all the metres and km with something like feet or miles, or something that is familiar to you.

*If you have taken calculus, it should be obvious to you that velocity is the derivative of the position, and acceleration is the derivative of velocity. Just as a side note, jerk is the derivative of acceleration. However, if you have never stepped into a calculus class (or rather, do not know calculus), just ignore what I just said (or rather, typed...).

Last edited: Jul 4, 2009