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Introduction |
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We have learnt about the motion of objects based on the definition of displacement, velocity and acceleration. |
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Force and Motion |
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A vegetable vendor applies force to push the cart, a driver applies force either to stop the car or to change the speed or direction of motion and a football player kicks the ball to set it in motion. |
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Resultant Force |
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Any object can be made to move by the application of force. Many forces can act simultaneously on a body. |
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Balanced and Unbalanced Forces |
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An unbalanced force acting on an object changes its speed or direction. The resultant of unbalanced forces is always greater than zero. |
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Galileo's Observation and Origin of Newtonian Mechanics |
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Aristotle and other medieval thinkers believed that the natural state of bodies is the state of rest. Galileo opposed this concept. |
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Inertia |
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It is clear from Galileo's experiments that all objects have a tendency to continue in their state of rest or of uniform motion until an external force acts on it. |
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Newton's First Law of Motion |
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A body continues to be in a state of rest or of uniform motion along a straight line unless an external force acts upon it. |
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Momentum |
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The force required to stop a moving body is directly proportional to its velocity. Thus the quantity of motion in a body depends on mass and velocity of the body. This quantity of motion defines a new physical quantity called momentum. |
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Newton's Second Law of Motion |
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Newton's second law of motion states that rate of change of momentum is directly proportional to applied force and takes place in the same direction as the applied force. |
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Applications of Newton's Second Law of Motion |
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In a cricket match a fielder moves his arms back while trying to catch a cricket ball because if he tries to stop the fast moving ball suddenly then the speed decreases to zero in a very short time. |
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Newton's Third Law of Motion |
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To every action there is an equal and opposite reaction. |
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An Experiment to Prove Newton's Third Law of Motion |
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Couple two spring balances A and B as shown in the figure. When we pull the balance B both the balances show the same reading indicating that both the action and reaction forces are equal and opposite. |
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Law of Conservation of Momentum |
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Action and reaction forces result in change in velocities of both the bodies which in turn change the momenta of these bodies. |
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Applications of Law of Conservation of Momentum, Newton's Third Law of Motion |
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When a bullet is fired from a gun, the gases produced in the barrel exerts a tremendous force on the bullet (action force). As a result, the bullet moves forward with a great velocity called the muzzle velocity. |
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Force of Friction |
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Due to friction we are able to walk on the surface of the Earth.The brakes applied in automobiles work only due to friction. |
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Question and Answers |
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Multiple Choice Questions |
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