Laws of Motion

    1. Linear momentum of the body is the quantity of motion contained in the body.
    2. Newton’s third law of motion signifies that forces in nature always occur in pairs. A single isolated force is not possible. Force of action and reaction act always on different bodies. Hence, they never cancel each other. Each force produce its own effect.
    3. Newton’s first law defines force; second law measures the force and third law gives us the nature of force.
    4. When the elevator move upward with uniform speed the apparent weight is equals to actual weight.
    5. When downward acceleration is greater than g. In that event, the person will rise from the floor of the lift and stick to the ceiling of the lift.
    6. The law of conservation is universal i.e. it applies to both, the microscopic as well as macroscopic systems.
    7. The principle of linear momentum is independent of frame of reference, though linear momentum depends on frame of reference.
    8. Second law of motion is the real law of motion.
    9. It is possible that the body may be moving with a constant velocity and net external force acting on the body is zero.
    10. A body can remain in rest position when external forces are action on it, if vector sum of all the forces acting on the body is zero.
    11. Normally, friction decreases with increase in smoothness. However, when the surfaces in contact are made too smooth by polishing, the binding force of adhesion increases and therefore, the friction increases. This is called ‘cold welding’.
    12. In moving a body over a rough horizontal surface, work has to be done only against the force of friction, which is a function of normal reaction/weight of the body. However, in moving a body up an inclined plane, work has to be done against friction as well as component of weight down the inclined plane.
    13. Friction is necessary evil.
    14. Without friction, motion cannot be started, stopped or transferred from one body to the other.
    15. Centripetal force is the force required to move a body uniformly in a circle. This force acts along the radius and towards the center of the circle.
    16.  Centrifugal force is a force that arises when a body is moving actually along a circular path, by virtue of tendency of the body to regain its natural straight line path.
    17. Centripetal force and Centrifugal forces, being the forces of action and reaction act always on different bodies.
    18. To avoid dependence on force of friction for obtaining centripetal force, the cyclist has to bend a little inwards from his vertical position, while turning.
    19. Friction is independent of the surface area of contact. Coefficient of friction is only depends on (i) material of the surface (ii) nature of the surface.
    20. A bucket containing water is rotated in a vertical circle because weight of water in the bucket is spent in supplying the necessary centripetal force. It is easier to maintain the motion than to start it because dynamic/kinetic friction is less than the force of limiting friction.
    21. Wheels are circular because they converts sliding friction into rolling friction.
    22. Streamline shape is given to fast moving vehicles to reduce the air friction.
    23. All types of friction are not self adjusting force. Only static friction is a self adjusting force.
    24. Force of friction is always oppose the relative motion.

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