# Speed or velocity?

1. Jul 7, 2007

### jaysun_83

What is the difference between speed and velocity?

2. Jul 7, 2007

### Meir Achuz

The usual meanings are that velocity is a vector, having magnitude and direction, while speed is just the magnitude of velocity.

3. Jul 7, 2007

### Mr Virtual

Suppose you are heading east with a speed of 1 m/s. If you change your direction towards north but keep your speed=1 m/s, then though your speed has not changed, your velocity changes. This is because velocity depends both on the speed with which one is going, and the direction in which he/she is going.
So how does velocity make a difference when used instead of speed? Suppose that you have to go straight north with a speed x m/s to reach a shop. Now you get out of your home and start walking southwards. What is your speed? x m/s. But with this speed, are you ever going to reach your market? No (unless you are brave enough to walk the whole length of earth, to reach that point). Why? If you are travelling with the required speed, what is the problem in reaching the market? The problem is that your direction is wrong or, in other words, your velocity is just opposite to what you should actually have.
So, are you now able to grasp the difference between speed and velocity?

regards
Mr V

4. Jul 7, 2007

### Danger

Just to add something that might clear up misconceptions that appear to be common: that change of direction is an acceleration, even though the speed remains constant.

5. Jul 7, 2007

### jaysun_83

Yeah, thanks Mr. Virtual. And thanks for the addition Danger, understanding that change of direction is an acceleration explains alot to me also.

6. Jul 7, 2007

### Danger

No worries, mate. The whole point is that 'acceleration' is defined as a change of velocity. If either the magnitude or the vector changes, then the term applies.