Speed Vs Velocity
Understanding the Difference
What makes velocity different from speed?
By Kashyap Vyas
Velocity is the rate of
change of motion in a specific direction. The definition seems very simple, yet
this vector quantity is complex in more ways than one.
The equation of average velocity is as follows:
Where,
Δx = position or displacement
Δt
= Time interval
The line or sometimes an
arrow over ν signifies that this value is a vector.
According to the equation,
the value of velocity increases as the time required for displacement
decreases.
So, we say high velocity when
the time required to cross a distance is low.
Likewise, low velocity is a
result of more time required to make a displacement.
Displacement or distance
You might have noticed that
we use the term displacement with velocity rather than distance.
There is a reason why we
chose to do so!
Distance is a scalar quantity
and is a measure of the magnitude of distance covered. It is just a number that
specifies how much an object has traveled from point A to point B.
Now imagine two points,
separated by a distance. There are infinite ways to connect them.
The shortest distance would be a single line connecting these two points.
However, you can also connect
two points using curved lines. But the distance will be different for every
type of line you choose to connect the two points.
We cannot say the same for
displacement because it is the measure of how far the second point is from the
reference point.
Therefore, displacement has
both magnitude and direction, making it a vector quality.
When defining velocity, you
are defining not just the rate of motion, but also its direction.
Speed vs Velocity
This is another comparison
that leaves many scratching their heads.
People often use the term
velocity and speed interchangeably, but they both have very distinct qualities.
Let us examine the equation
of speed.
There’s a striking similarity between the equation of speed and velocity. The equation tells us that speed is the rate of distance covered in a specific time frame.
But here, we are concerned
only about the distance.
Hence, speed is a scalar
quantity that gives us the rate of motion without any information about the
direction.
However, when we re-examine
velocity, we can see that distance is replaced by displacement. This gives us
an idea about the direction of the object.
Therefore, the velocity and
speed of an object are both defined differently.
For example, let us imagine
that a car travels at 20 kmph. If you ask a physicist, he/she would say that
the speed of the car is 20 kmph but the velocity is unknown.
But if you know that the car
is traveling at 20 kmph to the North, then the physicist would say that the
speed of the car is 20 kmph and its velocity is 20 kmph in the North direction.
Can the speed and velocity of an object be different?
There is always a comparison
drawn between speed and velocity regarding the motion of an object.
These two entities are constantly pitted against each other to see which is superior.
But there is no point
comparing vector and scalar quantities because they are distinct in their ways.
To give a rough idea,
consider an object traveling in a perfect circle at 20 kmph.
Since this is a perfect
circle and we have defined a constant rate of motion for it, speed and velocity
should be the same, right?
Wrong! In this case, the speed
of the object is constant, but the velocity is always changing.
This is because we consider
direction when defining velocity. So when an object travels in a circle, we
find that its direction is always in a state of change.
If we find out the direction
of that object at any given point, it will be tangential to the outline edge of
that circle.
Instantaneous Velocity and Instantaneous Speed
When we talk about the
standard equation, almost always, we are talking about average speed and
average velocity.
However, sometimes it is necessary to know the velocity or speed at an instant.
The velocity of an object at
a specific point in time is known as instantaneous velocity. The general
equation for instantaneous velocity is:
The speed of an object at a specific point in time is known as instantaneous speed. The general equation for instantaneous speed is:
Where,
x =
Displacement
s =
Distance
The most common example of
the measurement of instantaneous speed is a speedometer.
Speedometers show the speed
of an object in a particular instant, not its average value.
Why is velocity important?
Why bother having two equations for the rate of motion with respect to the time when you can simply use speed, which has a simpler equation?
The reason why velocity is of
high importance is that, in physics, the direction of an object carries great
importance.
Consider an airplane en route
to its destination. To get detailed information on the airplane, air control
terminals use velocity instead of the speed.
Vectors also play a very
important role in helping us determine how the velocity of one object may
influence another object.
For example, if two objects
collide in a nonlinear fashion, understanding their velocity before impact will
help us understand their behavior (direction and speed) after impact.
This is not possible if you
are using only the speed of the two objects. There are many more examples that
you can draw when it comes to the importance of velocity in physics.
Conclusion
Velocity often gets
overlooked because it doesn’t serve major roles outside of physics.
However, within the realm of
physics, it takes the center stage while speed is regarded with a lesser
importance.
Irrespective of how important both these quantities are, understanding the differences between velocity and speed gives us great insight into the different aspects of science and its applications.
Kashyap Vyas
is an entrepreneur, marketer and writer. He holds a Master’s degree in Thermal
Engineering with several research papers to his credit. Kashyap primarily
authors in-depth content in the science & technology space. You can find
more about him on LinkedIn.
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