Welcome students
Now we start rotational motion. Slightly difficult Agar chapters in Physics this chapter is slightly difficult then other chapters but one more thing you must understand the questions which are being asked Hindi examination are quite simple. Hence understand importance of this chapter. First thing in this chapter is the information of rigid body. We define rigid body as a body constituent girls particles are at fixed distance short. In other words relative configuration the body not change.
Now you understand concept of a big body now, till now talking we have been talking about. Objects now the objects are larger thought latest hot one by one first concept is of centre of mass. Centre of mass is defined as a. at a point where all the mass is supposed to be concentrated. Now we talk of types of motion. We know about linear motion, we also know about translational motion, in this chapter cross rotational motion.
Linear motion this type of motion in a straight line, in other words if a body travels in straight line we call it real motion linear motion. Now we talk of translational motion it is defined when all the particles, travel the same displacement. But in a rotational motion the displacement of constituent particles is not constant. Also locus of points displacement zero displacement are termed as access. Hence we must understand to define a rotational motion used to define the dot the particles which are farther away are having more displacement when the particles which are closer to the axis.
Next is the concept of moment of inertia. You very well know inertia is a property by virtue of which body resists change in motion, resistance to linear motion depends on mass only, while in rotational dynamics the resistance to motion depends not only on the mass but also on the relative position of the masses, hence moment of inertia depends on mass as well as distribution of mass.
Mathematical formula is given here. You must remember that before defining rotational we must define the axis.
Now we must try to relate linear motion with the rotational motion. In linear motion displacement is in metres, while in rotational motion the displacement is an angle. Similarly linear velocity is length divided by time , Rotational velocity defined as angle divided by time. Now linear velocity angular velocity related with the product of radius. Similarly linear acceleration and angular acceleration are related by product of radius. Here comes the concept of angular momentum also, linear momentum depends on mass and velocity and in rotation the angular momentum depends on moment of inertia and angular velocity. Similarly as we have defined force as rate of change of momentum we define torque as rate of change of angular momentum. Also we have conservation of angular momentum if applied torque is zero.
Standard moment of inertia all the bodies given in a table here. But when the axis changes, new moment of inertia can be found out by two theorems namely theorem of parallel axis and perpendicular axis. Some examples are also given to find the moment of inertia of different axis. At the last we must understand concept of rolling in the rolling body is having linear as well as translational motion and at the point of contact velocity is zero. One of the very important aspects is, when a body rolls down an inclined plane, in such a case velocity acceleration and time of journey formulas by conservation of energy principle so we use that. By mistake in the video instead of v squared V is written please note that.