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Answers
1- 4th option, as friction will be opposite to the direction of motion of object
2- 2nd option, because the object will not be moving so friction will be static
3- 1st option, it's a fact that rolling friction is lesser than static friction and static is lesser than sliding friction
Answer:
When a body slides over smooth and wet surfaces, the amount of interlocking of irregularities, of the two surfaces in contact, increases.
If a car moves eastwards, the force of friction acts southwards.
Friction depends on how hard the two surfaces press against each other.
4. The sole of shoes and the tyres of the vehicles are 'treaded' to decrease the effects of friction.
5. Lubricants can be liquids, semi-liquids or solids.
6. Friction can be increased by using ball bearings between the moving parts of machines.