# What is the difference between relative velocity and resultant velocity?

1. May 1, 2012

### suryanarayan

relative velocity and resultant velocity???also in a connected(with strings) pulley system,how can we calculate the acceleration and velocities of the pullies and the masses connected onto it???

2. May 2, 2012

### tiny-tim

hi suryanarayan!
resultant velocity is an alternative (and in my opinion less satisfactory) name for relative velocity

eg if the velocity of the wind is u, and the velocity of the plane relative to the wind is v,

then the velocity of the plane relative to the ground is u + v, which is sometimes called the resultant velocity since it is the resultant of the two vectors
if there's only one string, call the height of one of the pulleys "a", and see what happens to the heights of the other items

then differentiate once for speed, and twice for acceleration

(if there's n strings, you need to start with the heights of n items, and solve the simultaneous equations)

3. May 2, 2012

### sophiecentaur

Loosely, I'd say that relative velocity refers to how one observer in his own frame would see another moving object. Resultant velocity would be the velocity of an object (in some fixed reference frame) when there are more than one influences on its motion. OR, what you get when you start off by Resolving the motion of an object into two arbitrary directions (e..g. vertical and horizontal) to make your calculations easier. You then you add the two vectors together to get the overall resultant velocity.

The word 'resultant' is used for the sum of many vectors in general (forces, acceleration. magnetic field etc.)