Complex sentence: Free vibration occurs when a mechanical system is set off with an initial input and then allowed tpe of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring.
Split into simpler sentences: Free vibration occurs when a mechanical system is set off with an initial input and then allowed to vibrate freely. Examples of this type of vibration are pulling a child back on a swing and then letting go or hitting a tuning fork and letting it ring.