.... friction between the blade of ice skate and the ice surface. 2. loudness ; how noisy 4. Average is calculated by adding all the data...
If your " noisy " air-conditioner is a traditional one, you may add a piece of polystyrene (about...
rotation of propellors make a helicopter move. but the rotation of propellors is very noisy . so ear protector can protect the ear from damage.
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