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# Lesson_Text_2.1 - 1 Lesson 2.1 Force and Motion 1 The First...

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1 Lesson 2.1 Force and Motion 1. The First Law of Motion : A force is either a pull or a push. It is measured in a unit called newton (N). Force is a vector quantity; it has both magnitude and direction. An object at rest will keep on being at rest until some unbalanced force or a net force acts on it. In fig. 1 below, when the net force acting on an object is zero, it produces no motion. When the net force is not zero, there Forces are balanced. Produces no motion Forces are unbalanced. Produces motion Fig. 1 is an unbalanced force which makes the object move in the direction of the unbalanced force. In the same way, an object in motion will continue moving unless an unbalanced force acts on it. These two statements put together form the first law of motion which states as follows: An object will continue to be in a state of rest or of uniform motion unless an external unbalanced force acts on it. The tendency of an object to stay on in a state of rest or of uniform motion is called inertia . The only way to move an object at rest is to produce an acceleration on it. Similarly, the only way to stop an object from moving is to produce an acceleration on it. Therefore, we can define inertia as follows: Inertia is the tendency of an object to resist acceleration

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2 The ease with which an object can be put to motion or can be stopped from motion is determined by its mass . A very massive object has a much greater inertia than a less massive object. Therefore, mass of an object is a measure of its inertia. 2. The Second Law of Motion: What does an unbalanced force do? As a consequence of the first law, an unbalanced force changes the state of rest or state of motion of a particle. In other words, an unbalanced force produces acceleration. This leads to the second law of motion. An unbalanced force acting on an object will always produce an acceleration on it. No acceleration can be produced without an unbalanced force. The second law of motion gives us a relation between the unbalanced force and the acceleration it produces on an object. According to this law, the unbalanced force is directly proportional to the object. If an acceleration a m/s 2 is produced on an object by an unbalanced force F N, then we can write: F a This can be written as an equality using a constant as F = m a ….. (i) Where m is the mass of the object. This equation can be used to define one unit force called the newton. When m = 1 kg and a = 1 m/s 2 , then F = 1 N. In other words: A newton (N) is that amount of force which will produce an acceleration of 1 m.s -2 on an object of mass 1 kg. N = kg. m.s
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## This note was uploaded on 05/01/2011 for the course PHY 2048 taught by Professor George during the Fall '10 term at Edison State College.

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Lesson_Text_2.1 - 1 Lesson 2.1 Force and Motion 1 The First...

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