MadSci Network: Physics

Re: What is the relationship between velocity and acceleration?

Date: Fri Aug 3 09:15:07 2007
Posted By: Keith Jones, Head of Physics/Deputy Head, Rhyl HS
Area of science: Physics
ID: 1186077237.Ph

Hi Lisa.

Velocity is one of those words that everyday folk get confused about. They just think of speed and velocity as being the same thing. But we know different, don't we?!

A velocity doesn't just tell you how fast you're going; it also tells you which way you're headed.

For example, travelling at 13 metres per second *up* Maine Street is the same speed as travelling 13 metres per second *down* Maine Street, but because you're heading in different directions the velocities are not the same.

Now, acceleration is when there is a change of *velocity*, which could be a change of speed (getting faster/slower) or just a change in direction.

[added by MadSci Admin: So if you're not changing direction but the speed (the magnitude of the velocity) *IS* changing, then there is an acceleration. The average acceleration that causes the change in velocity is just the change in velocity divided by the time interval during which the change in velocity occurs.]

Now, let's return to this idea of a change of direction being an acceleration! This is why an object going round in a circle (e.g. whirling a bucket at the end of a rope!) needs a force (if you let go of the rope, away flies the bucket!). As the object goes round in a circle there is a continuous change of direction, which means a change of velocity, which means an acceleration. [added by MadSci Admin: In this case the speed (magnitude of velocity) is not (necessarily) changing.]

Hope this helps you Lisa.

Keith "Sunny" Rhyl, Wales, U.K.

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