Example: In a plant that furnishes نیروگاه تلمبه ذخیرهای, کار (فیزیک) and electrical work is done by machines like electric پمپs and مولد الکتریکیs. The pumped water stores mechanical work. The amount of energy put into the system equals the amount of energy which comes out of the system, less that amount of energy used to overcome اصطکاک.
