14)A moving object will never stop if there is nofriction. Actually it isimportantbecause it basically allows us to do everyday things: driving a car, picking up objects etc. Without it everything would just slip and slide, with nothing to grip onto. ...Friction"pushes" the wheels in a circular motion.

Helpful frictionPeople often usefrictionto slow things down. These brake blocks usefrictionto slow the bike wheels. When the skydiver opens the parachute, air resistance slows him down. ...Frictionalso wears engine parts, so they need replacing.

15)Elastic collision is a collision where the colliding objects bounce back without undergoing any deformation or heat generation. Inelastic collision is a collision where the colliding objects are distorted and heat is generated.2. In elastic collision, the momentum and total kinetic energy before and after collision is the same.3. In inelastic collision, the energy changes into other energies such as sound energy or thermal energy.4. The forces during elastic collision are conservative and the mechanical energy is not transformed into some other form of energy such as sound energy or thermal energy.5. The Forces during inelastic collision are non-conservative and mechanical energy is transformed into some other form of energy such as sound energy or thermal energy.6. An example of elastic collision is the movement of the swinging balls. An example of inelastic collision is an automobile collision.

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