answer 4th 5th & 6th please fast...
Answers
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4.) a.)School bags are provided with large wide straps to carry them because it increases the surface area in contact with the shoulder and reduce the pressure of the shoulder of the students shoulder.
b.)Air pressure goes on decreasing as we go higher up, so at high altitudes, the atmospheric pressure becomes less than the pressure exerted by the blood inside the body. This causes some of the blood vessels burst and the nose starts bleeding.
c.) Ball bearings are used in machines which have lot of movement in their working process. Ball bearings reduce the friction during motion, so that efficiency of the machines is increased, and they move in a smooth manner.
5.) Friction comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other. In sliding, the time given for interlocking is very small. Hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Because f this reason, sliding friction is less than static friction.
6.) The force that opposes the motion of an object is called force of friction. Example, when we walk, friction acts in the opposite direction we apply force to walk.The factor affecting friction are:1. The weight of the object,2. The type of contact between the two surfaces