1st Year Physics Chapter 3 Notes

• Definition of displacement: 
• Very important 1st year physics chapter 3 short questions from Punjab Textbook.
• Whenever a body moves from one position to another, the change in its position is called displacement. The displacement can be represented as a vector that describes how far and in what direction the body has been displaced from its original position. The tail of the displacement vector is located at the position where the displacement started, and its tip or arrowhead is located at the final position where the displacement ended. For example, if a body is moving along a curve as shown in Fig. 3.1 with A as its initial position and B as its final position then the displacement d of the body is represented by AB. Note that although the body is moving along a curve, the displacement is different from the path of motion. If r, is the position vector of A and r₂ that of point B then by head and tail rule it can be seen from the figure that d=r-r.  Average velocity does not tell us about the motion between A and B. The path may be straight or curved and the motion may be steady or variable. For example if a squash. ball comes back to its starting point after bouncing off the wall several times, its total displacement is zero and so also is its average velocity. In such cases the motion is described by the instantaneous velocity.
• In order to understand the concept of instantaneous velocity, consider a body moving along a path ABC in xy plane. At any time 1, let the body be at point A Fig. 3.2(b).lts position is given by position vector r.. After a short time interval af following the instant f. the body reaches the point B which is described by the position vector r₂. The displacement of the body during this short time interval is given by Ad=r2-r1 . The notation A (delta) is used to represent a very small change.
• The displacement is thus a change in the position of body from its initial position to its final position.
• Its magnitude is the straight line distance between the initial position and the final position of the body.
• When a body moves along a straight line, the displacement coincides with the path of motion as shown in Fig. 3.2. (a)
• The instantaneous velocity at a point A, can be found by making At smaller and smaller. In this case Ad will also become smaller and point B will approach A. If we continue this process, letting B approach A, thus, allowing At and Ad to decrease but never disappear completely, the ratio Ad/At approaches a definite limiting value which is the instantaneous velocity. Although Af and Ad become extremely small in this process, yet their ratio is not necessarily a small quantity. Moreover, while decreasing the displacement vector, Ad approaches a limiting direction along the tangent at A. Therefore,
• The instantaneous velocity is defined as the limiting value of Ad/Af as the time interval At, following the time t, approaches zero.
• Definition of velocity
• Definition of Acceleration  
• Velocity- Time Graph
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• Review of equations of uniformly accelerated motion
• Newton's laws of motion
• Newton is the first law of motion
• Newton's second law of motion
• Newton's third law of motion
• Definition of momentum 
• Momentum and neutral in the second law of motion
• Definition of impulse
• Law of conservation of momentum
• Elastic and inelastic collision
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• elastic collision in one dimension
• Force due to water flow
• Momentum and explosive forces
• Rocket propulsion
• Projectile motion
• Height of the projectile
• time of flight   
• range of the projectile
• application of ballistic missiles
• Very important 1st year physics chapter 3 long questions from Punjab Textbook.