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| Introduction |
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| The word force in common usage refers to a push or pull. The word Mass is also just as familiar as the word force. A super tanker is one that contains an enormous amount of mass. In comparison a coin does not contain much mass. |
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| During the seventeenth century Newton developed three important laws that deal with force and mass. Together they are referred to as "Newton's law of motion". They play an important role in classical physics to provide an understanding of the effects of forces acting on objects. |
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| Newton observed that an object at rest stays at rest until an outside force causes it to move. He also observed that an object in motion continues to move in the same direction until a force stops it or changes its direction. |
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| If you roll a smooth ball on a polished surface, it covers a greater distance before coming to rest than does a rough ball on a rough surface. Galileo Galilei on the basis of his experiment on inclined plane came to the conclusion that in the absence of friction and air resistance a moving body would continue sliding with a constant velocity for ever. However, we may point out that without friction rolling is not possible. |
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| All material bodies exhibit inability to change by themselves, their state of rest or of uniform motion in a straight line. This property is called inertia. Hence, a body at rest remains at rest and a body in motion continues to be in uniform motion in a straight line unless some external force acts upon it to produce a change. This is summarised in Newton's first law of motion. Newton stated his observation as the first law of motion. |
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| An object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an outside force. |
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| Inertia of rest |
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| When you sit in a chair, many forces act on your body. The pressure of the atmosphere pushes down on you and gravity pulls you towards the earth. You sit comfortable, because the muscles in your body push with equal force against the atmosphere above you. Your chair pushes up against the force of gravity to keep you from falling to the ground. All the forces acting on you are balanced. |
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| As you sit, your body obeys Newton's first law of motion. Your body is at rest, and it will remain at rest until some outside force moves it. Your body resists change. You have inertia. |
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| The word inertia comes from the Latin word iners, meaning "idle". Inertia is the tendency of an object to resist any change in motion. To overcome your inertia and move out of the chair, you must apply some kind of force to your body, the force you apply to overcome inertia must be greater than the forces that are acting on your body. |
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