Kinetics vs. Kinematics

Introduction

Kinetics and Kinematics, two essential arms of physics that investigate the motions of a body, have stark differences. While both the concepts are built strongly based upon Newton’s laws of motion, they show contrast in their fundamentals. Most of you are probably 7th graders trying to submit your assignments on time…or not, psst! We’ve still got you covered! Your secret’s safe with us :) So go on and dig in!

The main difference between kinetics and kinematics lies in the concepts they deal with. While kinematics deals with the mathematical explanations of an object’s motion, Kinetics deals with the factors that cause this motion in a body or an object. In other words, we can say that kinetics studies the cause and kinematics studies the result.

Since different topics are dealt with in both these concepts, different principles and laws come into the picture. Thus, kinetics uses pure physics while kinematics involves more mathematics.

Difference Between Kinetics and Kinematics in Tabular Form

Parameters of Comparison	Kinetics	Kinematics
Fundamentals	Focuses on studying the forces acting on the object that causes motion in an object.	Focuses on studying the motion of the object and calculating its mathematical elements.
Streams Associated	Kinetics is applied in biology, fluid dynamics, and chemistry along with physics.	Besides physics, kinematics is applied significantly in mechanics.
Determines	Calculating the force, torque, friction, gravity, etc.	Calculating the mathematical values of velocity, displacement, acceleration, etc.
Consideration of mass	The mass of the subjects is vital for the study of kinetics.	The mass of the subjects is not taken into consideration for any calculations.
Mathematical expressions	It does not involve a lot of mathematical expressions.	Kinematics includes several mathematical expressions that are defined in its principles.
Major Applications	Chemical kinetics, reaction kinetics, automobile design, etc.	Astrophysics, robotics, biomechanics kinematics, etc.
Other nomenclatures	Kinetics is also referred to as dynamics	Kinematics doesn't have any other references.

What is Kinetics?

Kinetics refers to the study that deals with researching the forces that are responsible for producing a motion on the specified body or object. After discussions in the 20th century regarding nomenclature, kinetics was widely regarded as dynamics, to avoid confusion with the term kinematics. Similar to kinematics, kinetics is built upon the concepts of newton’s second law. However, it deals with completely different topics. Kinetics lies in the WHYs branch of physics since it explains ‘why’ a certain motion occurs in an object, more specifically the forces that cause it. It is considered a branch of classical mechanics and is widely applied in automobile design.

When we mention the forces that cause a motion, it does not specifically mean forward motion. It could also mean forces that encourage motion in the opposite direction. Thus, it is an important factor to note that there are forces that can exist in different directions, overlapping simultaneously. This is why a physicist or a student studying kinetics tends to draw free body diagrams(FBD). These diagrams help us demonstrate the directions in which certain forces act, simplifying the problem posed and making the calculations easier.

Since we observed that there might be both kinds of forces, some that support the motion of an object in a certain direction and some that don’t. However, we do not consider them as forces that inhibit motion but instead consider them to be moving the objects in the opposite direction. Let us look at some of the causes of motion that can move the body in either of the directions:

Force: Simply put, a force can be defined as a push or a pull. Any external force acting upon a body will exert a certain acceleration or velocity upon the body that will cause the motion. This can be considered as either motion in the forward direction or opposite direction, depending upon the point of reference.
Torque: While force generally refers to acceleration upon objects that cause a straight-line motion, torque refers to the moment of force upon objects that cause a rotatory motion. Thus, angular momentum comes into the picture. Problems involving oscillating objects or a swing often involve the concept of torque. This can be either in the forward direction or the opposite direction, depending on the swing.
Friction: An inhibiting force that acts when an object slides over another object is known as friction. This restricts the movement in any given direction the exerted force acts upon. It is always applied in the direction opposite to the exerted force
Gravitational force: Problems that involve objects flung into the air directly or at an angle i.e., projectile, deal with the concept of gravity. Gravity reduces the flight time of an object as it applies force toward the earth.

While we are still on the topic of falling objects, let us bring the concept of energy conversion into kinetics. When an object is at a certain height, it stores a certain amount of potential energy. The moment it is released, the potential energy is converted to kinetic energy along the course of the fall. Once it falls, the kinetic energy converts into potential energy again. However this is subjected to the point of reference as the value of potential energy depends on the height of the object from a ground-level i.e., the point of reference. Thus, this supports the fundamentals of conservation of energy that state that ‘energy is neither created nor destroyed, only converted from one form to another!

Chemical Kinetics

However, physics is not the only stream to which the fundamentals of kinetics are limited. Another major branch of kinetics is known as Chemical kinetics, which deals with investigating the elements of a chemical reaction throughout it. This includes:

Identifying the intermediate steps in a reaction
Identifying and investigating the supporting and inhibiting factors in a chemical reaction i.e., inhibitors and catalysts.
Establishing fundamental equations i.e., rate laws for the chemical reaction.

This branch of chemical kinetics is also referred to as reaction kinetics.

What is Kinematics?

Deriving its nomenclature from the Greek term: Kinesia, which translates to motion, Kinematics is the study of describing the motion of objects by equations, graphs, and diagrams through the fundamental mathematical expressions. The whole concept of kinematics was built and expanded on Newton’s second law which provides the mathematical representation, that force is the product of mass and acceleration. However, Kinematics does not deal with calculating these forces. Instead, it focuses on calculating velocity, acceleration, and other such elements that result from the motion of a body.

With the help of certain fundamental equations, we can easily calculate the position of an object at any certain point in time. Besides this, when a certain set of factors are established for a particular object i.e., the velocity, the acceleration, the initial position, etc. any missing factor such as the final position and distance can be calculated through the equations. Thus, kinematics allows us to calculate the instantaneous positions of an object and their instantaneous behavior when enough values are known. Owing to this feature, Kinematics is said to provide us with the ‘geometry of motion’.

Thus kinematics helps predict the behavior of real-life models through mathematical expressions that provide accurate results and avoid any potential mishaps.

The Fantastic Four!

Clearly, kinematics exploits the concept of these ‘fundamental mathematical equations’ that have been mentioned repetitively. It is now time that we explain what exactly these expressions are-

v_f=v_i+a*t
d=(v_f+v_i)*t/2
v_f²-v_i²=2*a*d
d=v_i*t+(1/2)*a*t² where,

d= displacement of the object
V_i= initial velocity of the object
V_f= final velocity of the object
a= acceleration of the object
t= time for which the motion of the object lasted / instant of motion where other elements are required to be determined.

Concepts of Kinematics:-

Kinematics was initially applied to objects that move in a straight line, for convenience. Soon the question arose of how the concepts would differ if the object were not to follow a purely straight line. Thus, the circular motion came into the picture along with satellite motion. Kinematics concepts were first analyzed and then extended to discuss the accommodation for the required changes in the established mathematical equations.

Displacement:

The term displacement is defined as the shortest route between any two points. This can also be defined as the length of a straight line between any two points.

However, it is a common misconception that the words ‘distance’ and ‘displacement’ can be used interchangeably. The distance an object travels is not necessarily the displacement of an object.
There are infinite routes that can exist from any said point ‘a’ to another point ‘b’ and they can have different path lengths. Displacement is defined as the shortest of all path lengths.
It is denoted by ‘d’ in most cases.

Velocity:

It is the displacement of an object divided by the time taken.
It can be negative if the object moves backward when taken concerning the coordinate system. Thus it is a vector quantity.
It is not to be considered equivalent to speed, which is a scalar quantity. It can only be positive, representing the only magnitude and no direction.
We can find both average velocity and instantaneous velocity for a given object, considering all the required parameters are provided.
It is denoted by ‘v’ in most cases, with a suffix of ‘i’ or ‘f’ when needed to represent initial and final velocities.

Acceleration:

The term acceleration can be defined as the rate of change of velocity per unit of time.
Since acceleration is calculated with velocity or distance, it too can be a negative quantity. Thus, it is a vector quantity.
The sign of the value of acceleration obtained upon calculation depicts whether the acceleration is increasing or decreasing i.e. if the velocity is increasing or decreasing at that instant.
The value of acceleration depicts the magnitude by which the velocity changes at that instant.

Main Differences Between Kinetics and Kinematics in Points

Kinematics deals with the study of different motions in an object and calculating the elements mathematically that result from the motion. On the other hand, Kinetics deals with and studies the concepts that cause such motions in an object/ body.
Kinematics is majorly used and associated with physics and mechanics whereas kinetics, however, is not limited to physics. It stretches to fluid dynamics, chemistry, and biology too!
As previously mentioned, kinetics deals with the cause of a motion. Thus it determines different forces acting upon a body, such as torque, gravity, and friction. Kinematics, however, deals with the motion itself. It studies different elements that result from the forces that cause the motion, such as displacement, velocity, acceleration, etc. This explains better how kinetics differs from kinematics at its very fundamentals.
Kinetics requires the values of masses of the subjects involved since all the calculations of forces involve the consideration of mass. Kinematics doesn’t require the values of mass to calculate different factors. Thus, it does consider mass.
Kinetics does not generally call for any requirement of mathematical expressions. On the contrary, fundamental mathematical expressions, established in the principles, are very crucial for any calculations carried out whenever required.
Kinetics is also sometimes referred to as dynamics whereas kinematics does not have any other nomenclature.
Kinetics is greatly applied in the files of chemistry and has a separate area of study dedicated to it, called chemical kinetics. It is also called reaction kinetics. Besides this, kinetics is applied in automobile design. Kinematics is applied in major areas of science that have separate fields dedicated to them, similar to kinetics. Some examples are biomechanics kinematics, astrophysics, robotics, etc.

Conclusion

With great hope that you children(or not!) have clarified most of your doubts, we will now summarize our observation by stating that Kinetics is more related to the WHYs branches of physics, investigating and studying the forces that cause a certain motion whereas Kinematics is related to the investigations that deal with the results of these motions i.e., displacement, acceleration, etc.

References

Introduction
Kinetics vs. Kinematics
Difference Between Kinetics and Kinematics in Tabular Form
What is Kinetics?
What is Kinematics?
Main Differences Between Kinetics and Kinematics in Points
Conclusion
References

Difference Between Kinetics and Kinematics

Introduction