# Can anyone please tell me the definition of Time, Speed, and Velocity please?

Jun 6, 2016

See below

#### Explanation:

Time is an observed phenomenon associated with an indefinite record of changes occurring in the known environment and universe. The human sense of changes from past, through present and to future.
It is one of Seven Base physical quantities which are distinct in nature and cannot be expressed in the form of other quantities. Its unit is second. Time is used to define other quantities.

Historically time has been closely related with space. These two merging to from spacetime continuum in Einstein's theories of relativity.

Before defining Speed and Velocity we must first understand Distance or Displacement. When an object changes its position from a location $A$ to another location $B$, the distance or the displacement has two attributes. Amount of change and direction of
change. As such it is a vector quantity and is denoted as
$\vec{d} = | \vec{d} | \hat{r}$
where $| \vec{d} | \mathmr{and} \hat{r}$ are the magnitude or the scalar part and unit direction vector respectively.

Now the rate of change of its position is called Velocity. As such it is also a vector quantity. It is denoted as $\vec{v}$.

And Speed of an object is the magnitude of its velocity. It is a scalar quantity. Therefore, once direction of the speed is indicated it becomes velocity.

Mathematically,

Speed $v = | \vec{v} | = | \dot{\vec{r}} | = | \frac{\mathrm{dv} e c r}{d t} |$
where it is magnitude of the derivative of the position vector $\vec{r}$ with respect to time