#### notes

**Measuring The Rate Of Motion – Speed With Direction:**

The rate of motion of an object can be more comprehensive if we specify its direction of motion along with its speed.

The quantity that specifies both these aspects is called velocity.

Velocity is the speed of an object moving in a definite direction.

The velocity of an object can be uniform or v ariable. It can be changed by changing the object’s speed, direction of motion or both.

When an object is moving along a straight line at a variable speed, we can express the magnitude of its rate of motion in terms of average velocity.

In case the velocity of the object is changing at a uniform rate, then average velocity is given by the arithmetic mean of initial velocity and final velocity for a given period of time.

That is,

Average velocity = `("Initial velocity" + "Final velocity") / 2`

Mathematically, v_{av} = `"u" + "v"/2`

Where v_{av} is the average velocity, u is the initial velocity and v is the final velocity of the object. Speed and velocity have the same units, that is, m s^{–1} or m/s.