Classical mechanics include kinetics and kinematics, which deal with the motion of objects or bodies in different spaces. The main distinction between kinetics and kinematics is that kinetics is associated with the study of various forces that result in motion. Kinematics, on the other hand, is concerned with the study of real motion of things or bodies without keeping in mind the force that creates the motion.
What is Kinetics?
Kinetics deals with the absolute motion of an object. It explains how a body responds when a force or torque is applied to the body. It is the study of forces that are acting on an object under a particular mechanism.
Kinetics focus on the different types of motion such as rotational motion in which the object experiences force or torque. e.g. When a car is moving, in this case, it possesses some amount of kinetic energy.
Kinetic energy is defined as the energy of motion or movement of an object, rather than in its position. The faster the motion of an object, the higher will be the kinetic energy. Kinetic energy can be calculated as,
K.E. = 1/2 mv^{2}
where,Â
- K.E. = Kinetic energy,
- m = mass of the object (kg or g),
- V = velocity of the object.(m/sec),
The Units of K.E = Kg (m/sec) or joules. Therefore kinetic energy is directly proportional to the mass of the object and to the square of its velocity
What is Kinematics?
Kinematics is a branch of dynamics that deals with motion of objects (bodies), points or group of objects, considering the mass and force, ignoring the cause of its motion. Some refers to the study of kinematics as the “Geometry of motion”.It deals with any type of motion of a particular object.Â
To know the motion of the object it focuses on the trajectories of the points, lines, and various other geometric objects. It also focuses on the various different properties like velocity and acceleration. The study of kinematics is mostly used in astrophysics, mechanical engineering, robotics, and biomechanics.
Formulas of Kinematics:
It has 4 formulas in which they are related to displacement, time, velocity and acceleration.
- a = (v – u)/tÂ
- (v + u)/2 = d/t
- d = ut + 1/2 at2Â
- v^{2} = u^{2 }+ 2ad
whereÂ
- a = acceleration,
- d = displacement,
- t = time interval,
- u = initial velocity,
- v = final velocity.
Difference between Kinetics and Kinematics:
Kinetics |
Kinematics |
Kinetics deals with the absolute motion of an object. It explains how a body responds when a force or torque is applied to the body. It is the study of forces that are acting on an object under a particular mechanism. | Kinematics is a branch of dynamics that deals with the motion of objects (bodies), points, or groups of objects, considering the mass and force, ignoring the cause of its motion. Some refer to the study of kinematics as the “Geometry of motion”. It deals with any type of motion of a particular object.Â |
Kinetics focus on the different types of motion such as rotational motion in which the object experiences force or torque. | It explains the terms such as acceleration, velocity, and position of the object. |
In this, the mass of the object is considered. | In this, the mass of the object is not considered. |
It is used in the design of automobiles. | It is used to study the movement of celestial bodies. |
In kinetics, force is considered. | In kinematics, force is not considered. |
It deals with absolute motion. | It deals with relative motion. |
It does not involve any mathematical expressions. | It involves mathematical expressions. |
It is used in several streams of science like chemistry and biology. | It is used in limited areas in physics and it is more specifically used in mechanics. |
It consists of the masses of particulars while explaining a phenomenon. | It includes different forces like a gravitational force that works between two systems. |
It is also called dynamics. | It is also called the geometry of motion. |
Sample Questions
Question 1: What are the examples of Kinetics and Kinematics?
Answer:
Examples of Kinetics:
- Friction.
- TorqueÂ
- Gas KineticsÂ
- Polymerization.
- Combustion.
- Catalysis.
- Nanoparticles Production
Examples of Kinematics:
- Throwing a ball or stone. (vertical motion)
- Moving objects like car, animals etc (horizontal motion).
- Firing a cannonball, Shooting a bullet from gun (Projectile motion).
Question 2: A man is moving in a car with a velocity of 8 m/s, then he suddenly stops the car. Does he brake to stop completely with an acceleration of -4m/s^{2}?
Answer:Â
Given that,Â
Initial velocity u = 8m/s
Final velocity v = 0 m/s
Acceleration a = – 4m/s^{2}
From kinematics formula,
v^{2} = u^{2} + 2ad
0^{2} = 8^{2} + 2 Ã— -4 Ã— d
64 – 8d = 0
8d = 64
d = 64/8
= 8 m
Therefore, the distance travelled by man in car is 8 m.
Question 3: A particle is initially at rest and moves with a velocity of 5 m/s for 3 s. Find the acceleration?
Answer:
Given that,
Initial velocity u = 0
Final velocity v = 15 m/s
Time t = 3 sec
From kinematics formula,
a = (v – u)/t
a = (15 Â – 0)/3
a = 15/3
a = 5 m/s^{2}Â
Therefore the acceleration of it is 5 m/s^{2}
Question 4: A ball is moving with a velocity of 8 m/s for a distance of 1200 m. Find the time taken to reach that distance?
Answer:
Given that,
Initial velocity u = 8 m/s
Final velocity v= Â 0 m/s
distance travelled d = 1200 m
From kinematics formula,
d = (v + u)t/2
1200 = (0 + 8)t/2
1200 Ã— 2 = 8t
2400 = 8t
t = 2400/8
= 300 s
Therefore the time taken to reach that distance is 300 s.
Question 5: A car with a mass of 500 kg is moving with a velocity of 10m/s. Calculate the kinetic energy of the car?
Answer:
Given that,
mass of car m= 500 kgÂ
velocity v = 10m/sÂ
Formula of kinetic energy,Â
K.E = Â½ mv^{2}
K.E= Â½Ã— 500 10 Ã—10Â
K.E = 25000JÂ
Therefore, the kinetic energy of it 25000 JÂ
Question 6: A tennis ball is moving at a velocity of 4m/s and it has a kinetic energy of 80J. Calculate the mass of the tennis ball?Â
Answer:Â
Given that,Â
velocity v = 4 m/sÂ
K.E = 80JÂ
Formula of kinetic energy,Â
K.E = Â½mv^{2}Â
80 = Â½ Ã— m Ã— 4 Ã— 4Â
m = 160/16
= 10 kgsÂ
Therefore, the mass of tennis ball is 10 kgs