# Speed vs Acceleration?

1. Oct 30, 2006

### MoMo

Could someone please explain what the difference is between speed and acceleration? I would sincerely appreciate it, thanks!

2. Oct 30, 2006

### Cyrus

What are their definitions?

3. Oct 30, 2006

### MoMo

speed - a scalar quantity, which refers to how fast an object is moving

acceleration - a vector quantity, which is defined as the rate of change of velocity

...erm let me add velocity's def here as well:

velocity - a vector quantity, which refers to the rate at which an object changes its position and is computed from the displacement/time ratio

See, what confuses me is when I compare speed and acceleration in terms of a car. When a car accelerates, doesn't its speed increase? What does velocity have to do with these two terms as well? Btw thanks again :-)

4. Oct 30, 2006

### geoffjb

Acceleration is the rate of change of the velocity. So as long as acceleration and velocity are in the same direction, acceleration will result in increased velocity.

Don't forget that when you hit the brakes, the car also accelerates--just in the opposite direction to the velocity vector (or at least you hope it does).

Velocity is the speed of the car and its direction.

Last edited: Oct 30, 2006
5. Oct 30, 2006

### MoMo

That makes sense. Thank you :-)

6. Oct 30, 2006

My pleasure.