1st Year Physics Chapter 5 Notes

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• Circular Motion: We have studied velocity, acceleration and the laws of motion, mostly as they are involved in rectilinear motion. However, many objects move in circular paths and their direction is continually changing. Since velocity is a vector quantity, this change of direction means that their velocities are not constant. A stone whirled around by a string, a car turning around a corner and satellites in orbits around the Earth are all examples of this kind of motion.  In this chapter we will study, circular motion, rotational motion, moment of inertia, angular momentum and the related topics.      
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• Angular displacement: Consider the motion of a single particle P of mass m in a circular path of radius r. Suppose this motion is taking place by attaching the particle P at the end of a massless rigid rod of length/whose other end is pivoted at the centre O of the circular path, as shown in Fig. 5.1 (a). As the particle is moving on the circular path, the rod OP rotates in the plane of the circle. The axis of rotation passes through the pivot O and is normal to the plane of rotation. Consider a system of axes as shown in Fig. 5.1 (b). The z-axis is taken along the axis of rotation with the pivot O as origin of coordinates. Axes x and y are taken in the plane of rotation. While OP is rotating, suppose at any instant 1, its position is OP,, making angle with x-axis. At later time ( At, let its position be OP, making angle + with x-axis (Fig. 5.10). Angle 40 defines the angular displacement of OP during the time interval At For very small values of 40, the angular displacement is a vector quantity.  
• Important from 1st year physics chapter 5 important short questions Punjab Textbook.
  The angular displacement 40 is assigned a positive sign when the sense of rotation of OP is counter clock wise. The direction associated with A is along the axis of rotation and is given by right hand rule which states that Grasp the axis of rotation in right hand with fingers curling in the direction of rotation; the thumb points in the direction of angular displacement, as shown in Fig 5.1 (d). Three units are generally used to express angular displacement, namely degrees, revolution and radian. We are already familiar with the first two. As regards radian which is Sl unit, consider an ars, of length 5 of a circle of radius r (Fig 5.2) which subtends an angle wat the centre of the circle. Its value in radians (rad) is given as arclength radius S S=r rad (where 8 is in radian) rad of (5.1). If OP is rotating, the point P covers a distance s = 2 ar in one revolution of P. In radian it would be 52-2 F 1 revolution = 2nrad = 360" 1 rad 360 2π 57.3.
• Important from 1st year physics chapter 5 solved exercise Punjab Textbook.
• Angular velocity
• Angular acceleration                                             
• Relation between angular and linear velocities
• Equations of angular motion
• Centripetal force
• Moment of inertia
• Angular momentum
• Law of conservation of angular momentum
• Rotational kinetic energy
• The rotational kinetic energy of a disc and hope                             
• Artificial satellites
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• Real and Apparent weight
• Weightlessness in satellite and gravity-free system
• Orbital velocity
• Artificial gravity
• Geostationary orbits
• Communication satellite 
• Important from 1st year physics chapter 5 solved numericals Punjab Textbook.
• Newton's is Einstein's views of gravitation