Fatemeh asked the following question – “When you want to use a vacuum cleaner, you pull the wire out until you got the length you needed. The the length of the wire gets fixed. Then, when you want to rolls up the wire, you pull it out a bit and then you release it,it rolls up with the power of hands only.”
Fatemeh, I think this is a question about springs. To give me time to think I passed the question to my friends.
Many thanks team.
Fatemeh. I suspect the vacuum cleaner observation is linked to springs. When you pull the power lead out you are likely to be extending a spring. Your energy which you apply to pulling the power lead is being stored by the spring. When you stop pulling a device within the vacuum cleaner is applied to stop the spring from unwinding and losing it’s stored energy (the proper scientific term is stored potential energy) …….until you give another little tug which releases the device and the stored energy is then used to pull the lead back into the vacuum cleaner.
To experience the way in which a spring can store energy try making one yourself from a paperclip. Get a big paperclip and try to wind it around a pencil.