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| Momentum |
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| Momentum is another vector quantity which has the same direction as that of velocity. Momentum is a property of the body possessed by virtue of its mass and velocity. It is the product of mass of the body and its velocity. |
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| Momentum = mass x velocity |
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| p = m x v |
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| S.I Unit of momentum = kg x m s-1 |
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| Momentum |
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| It is a dynamic property which a body possesses due to the combined effect of mass and velocity. |
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| A rolling marble can be stopped more easily than a bowling ball moving at the same velocity. Both objects have inertia of motion, or momentum. However, the bowling ball has more momentum than the marble. The momentum of a moving object has a large momentum if it has a large mass, a large velocity, or both. |
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| Momentum doesn't change unless the velocity of mass changes. However, momentum can transfer from one object to another. For example, when a ball rolling across a pool table hits another ball, the momentum of the first ball transfers to the second ball. Maintaining and transferring momentum is called the law of the conservation of momentum. |
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| A truck requires a larger force to set it in motion when it is heavily laden than when it is empty. Likewise, far more powerful brakes are needed to stop a heavy goods vehicle than a light car moving with the same sped. The heavier vehicle is said to posses a greater quantity of motion or momentum than the lighter one. |
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| In the early seventeenth century the German astronomer, Johann Kepler, had shown that the planets move in elliptical paths or orbits round the sun, but he was unable to explain why. It was left to Sir Isaac Newton to offer a satisfactory explanation based on the first law of motion and the law of universal gravitation. Newton pointed out that the planets move in curved paths because the sun is attracting them. No slowing up occurs, since there is no retarding force. The planets move in the vacuum of space, carrying their atmospheres with them. If the attraction of the sun suddenly ceased, a planet would continue to move in a straight line making a tangent with its original orbit. |
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| It is important to realise that, once a body is moving with uniform speed in a straight line, it needs no force to keep it in motion provided there are no external opposing forces. |
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| The tendency of a body to remain at rest or, if moving, to continue its motion in a straight line is described as inertia. For this reason, Newton's first law is sometimes called "the law of inertia". We shall now go on discuss the motion of a body when it is being acted upon by a force. |
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| When two bodies, a heavy one and a light one, are acted upon by the same force for the same time, the light body builds up a higher velocity than the heavy one. But the momentum they gain is the same in both cases. This important connection between force and momentum was recognised by Sir Isaac Newton and expressed by him in a second law of motion. |
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| If no external force acts on a system in a particular direction then the total momentum of the system in the direction remains unchanged. |
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