Introduction to Work, energy, conservation of energy and collision
ü We all know that it is hard work lifting a heavy box from one platform to another in a railway station. Similarly we know that children need lots of energy as they grow up.
ü We feel tired if we run a hundred meters in twenty seconds, whereas we could walk that distance easily in a couple of minutes.
ü These are some common sense notions of work and energy which can however be precisely defined and measured in physics.
ü These definitions are measurements can be used consistently to describe and predict the behaviour of bodies and thus can form very powerful tool for analysis of physical systems.
OBJECTIVE
ü In the previous chapter we studied the Newton’s laws of motion to understand how objects move under the influence of force acting on them or the relation between the force and the acceleration produced by this force.
ü In this chapter however, we will study the situation where one is not interested in such an exhaustive study of object’s motion rather desires to relate the final velocity of an object to the forces acting on it without going into the deeper details how the object acquired that velocity. The work-energy theorem solves this purpose.
PRE-REQUISITE
Velocity
ü Rate of change of position of an object is known as its velocity.
V = dx /dt
Acceleration
ü Rate of change of velocity of an object is known as its acceleration.
a= dv / dt = d²x / dt²
Force
ü Force is a push or pull which tends to change the position of the object on which it is applied.
Newton’s first law of motion
ü It states that every object persists in its natural state of motion i.e. continues to be at rest or moves in a straight line with uniform (constant) velocity. (This is what is meant by natural state of motion); In the absence of a net external force acting (impressed) on it.
Newton’s Second law of motion
Newton’s Third Law of Motion
ü When ever a body exerts a force on a second body, the second body always exerts a force of equal magnitude but opposite in direction on the first one.
Conservation of Energy
ü Whenever one form of energy is transformed into other forms, the total amount of energy before transformation is always equal to the amount of energy after transformation, i.e., the total amount of energy remains conserved.