Mechanics is the study of motion. Everywhere we look, objects are moving. We see people moving on roads, some using vehicles. Actually, everything we know is constantly in motion. Celestial objects and our Earth are always moving. Even objects that appear to be still have atoms and molecules that vibrate in continuous motion.
Our formal study of physics starts with kinematics, which is the study of motion without considering its causes. The term "kinematics" comes from Greek and means motion. In this unit, we will only focus on the motion of objects, without concerning ourselves with the forces that cause or change their motion.
If with passage of time an object does not change its position then it is at rest with respect to an observer and if it is changing its position then it is in motion.
When we look around us, we observe that many objects do not change their position. Thus we consider them at the state of rest. For example, a bench in a park fixed under a tree is at rest as there is no change in its position with respect to us while standing near it with the passage of time. On the other hand, we also observe that many objects do change their position from one place to another. Hence we consider them to be in the state of motion. For example, a car is in motion if there is a change in its position with time.
Interestingly objects can be at rest and in motion at the same time. It looks simple to distinguish the rest from motion, for example, a car starts, it changes its position with reference to its surrounding, we say that the car is moving.
However, we know that Earth is spinning on its axis, so the car along with its road is also in motion. Not only this but Earth is also moving around the sun and the sun along with the rest of the solar system are also moving through our milky way galaxy. Apart from this, our galaxy is also traveling through space. How can we say that our car is at rest? This is why when we state an object to be at rest or in motion, we specify it with reference to some observer.
Looking at the motion of objects, we see that objects move differently. These different types of motion can be broadly categorized into three types: translatory motion, rotatory motion, and vibratory motion.
If all points of a moving object move uniformly in the same direction, such that there is no change in the object's orientation, the object is said to be undergoing translatory motion (also termed as translational motion).
A basketball is shown in figure 2.1 as an example of translatory motion. All the three points 'P,' 'P,' and 'P,' move parallel to each other and there is no change in its orientation relative to a fixed point.
When an object rotates on its own axis (a line passing through the object), the object is said to be undergoing rotatory motion (also termed as rotational motion). A basketball in figure 2.2 is again shown as an illustration of rotational motion.
The point 'P' is rotated around an axis of rotation passing through the center of it.
When an object is moving forward and backward repeatedly about a mean position (certain fixed position), the object is said to be undergoing vibratory motion (also termed as vibrational motion). A basketball in figure 2.3 is shown as an example of vibrational motion.
The basketball moves back and forth about the mean position. Figure 2.4 shows some daily life examples of types of motion.
Rectilinear motion is the translatory motion of the object in a straight line path. For example, the motion of a train on track, motion of a gunshot, and motion of a falling apple.
Circular motion is the translatory motion of an object in which it moves in a curved path. For example, the motion of a football when kicked, the motion of a roller coaster, and the motion of a vehicle in a turn are examples of curvilinear motion. Circular motion is a special case of curvilinear motion in which the radius of rotation remains constant and the object moves along a circular path.
An object can have any combination of these types of motion.
Random Motion is the translatory motion of an object with no specific path. For example, kites flying through the sky, motion of clouds, and the motion of a butterfly.
Translational motion is seen in various scenarios, covering a wide range of situations. Whether in engineering, physics, or everyday life, objects frequently display this type of motion. It is crucial to comprehend the specific motion type in order to accurately analyze and describe the behavior of moving objects.