When pushing a child on a swing, you must give them a push periodically to keep them moving. This seems to go against the law of inertia and the conservation of energy. Explain why the child needs a push periodically to keep moving. (8.P.2A.3, 8.P.2A.5)
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2 points
Energy is lost over time slowing down the swing.
All objects will naturally come to rest over time.
A wind must have been blowing in the opposite direction.
Friction provides an outside force slowing the swing down.
The correct answer is: Friction provides an outside force slowing the swing down.
When a child is swinging, there is friction between the swing and the air molecules, as well as between the swing and the ropes or chains holding it. This friction acts as an outside force that opposes the motion of the swing and causes it to slow down over time. In order to counteract this frictional force and keep the swing moving, the child needs periodic pushes to add energy to the swing system and maintain its motion.