Hello and welcome to physicscatalyst.com. In this video learn about the concept of speed
So let's first define what is speed. Speed is defined as distance covered per unit time
So in form of mathematical formula we can write speed is equal to distance divided by time
To understand this concept further let us consider a cyclist who covers 30 meters in
a time of 3 seconds. Now the speed of this cyclist would be speed is equal to distance
travelled divided by time taken to cover this distance which is equal to 30 meters divided by
3 seconds. So the speed of cyclist is 10 meters per second. Now here meter per second is the
unit of measurement of a speed. So there are many units for the measurement of a speed
and for long distances which are covered using motor vehicles we generally use kilometer per
hour or mile per hour as the unit of speed and for shorter distances we generally use
meter per second as the unit of speed. If you talk about systems of units then in SI system of units
meter per second is the unit of speed and another system of units that is generally used is
CGS system of units and in CGS system of units centimeter per second is the unit of a speed. Also
the dimensions of speed is m to the power 0, l to the power 1 and t to the power minus 1
Here this m is the dimension of mass, l is the dimension of length and this t is the dimension
of time. Now there are some very important points that you must remember about speed. So first
point is speed is a scalar quantity. This is because it has only magnitude and no direction
So while specifying the speed of a moving object or a body we only specify the magnitude
of the speed and the direction of speed is not taken into consideration
Another important point about speed is as we know that speed of a object is distance travel
divided by time taken and we know that distance travelled by an object is either positive
or zero. It cannot be negative. So speed of the object under consideration may be positive
or zero but it can never be negative. Let us now have a look at different types of speed. So first one is uniform speed
Uniform speed. So an object is said to be moving with uniform speed if it covers equal distance
in equal amount of time
and it doesn't matter how small these time intervals may be. To understand this further
let us consider a person moving along x-axis and this person is covering 2 meters of distance
in 60 seconds. Now if this person keeps on moving a distance of 2 meters in next 60 seconds
and then after that it again covers a distance of 2 meters in this 60 seconds then this person
is said to be moving with uniform speed and for example if this person covers 2 meters
in 60 seconds for first interval and in second interval it covers 3 meters in 60 seconds
then in this case the person is not moving with uniform speed. Now second type of speed
is variable speed. Now an object is said to be moving with variable speed if it covers
unequal distances in equal intervals of time. For example, during first interval of motion
if a person is traveling 2 meter in 60 seconds and in second interval of motion he is traveling
3 meter in 60 seconds and in third interval he is again traveling 2 meter in 60 seconds
then in this case you can note that the person is traveling unequal distances in equal amount
of time. So in this case the moving person has a variable speed or we can say that speed of the
person in this case is variable. Now third type of speed that we would discuss here is average speed
Now we calculate average speed of a moving object or body in the cases when the body is moving with
variable speed in general. So for an object moving with variable speed the average speed
is the total distance traveled by the object divided by total time taken to cover that
distance. Now fourth type of speed is instantaneous speed. Now instantaneous speed is the speed of
the object at a particular instant of time or at a particular point or at a particular time in its
path. Now to explain further let us consider an object covers a distance delta x in small time
interval delta t then in this case average speed is given by delta f upon delta t
Now the limiting value of this average speed is when this time interval delta t approaches zero gives us the instantaneous speed at any time t
So instantaneous speed is given by the relation v is equal to limit delta t tends to zero
delta x upon delta t which is also written as dx upon dt. Now here this dx upon dt
is the first order derivative of distance x with respect to time t
So this is it for now thanks for watching