Question

УМОЛЯЮ! Почему дверь, поставленная наклонно, либо сама открывается, либо сама закрывается? За счет какой энергии совершается эта работа? Не нарушается ли здесь закон сохранения энергии?

Answer 1

Нет не нарушается потому что дверь повешенная правильно находится в состоянии  безразличного равновесия ( любое ее отклонение не приводит к возникновению дополнительной силы)

дверь повешенная неверно находится в состоянии неустойчивого равновесия  ( тогда дверь сама открывается) или устойчивого равновесия ( тогда дверь сама закрывается)
это происходит за счет потенциальной энергии тела в поле тяготения Земли

Answer 2

Why does a door placed at an angle either open or close on its own? What energy is responsible for this work? Does it violate the law of conservation of energy?

When a door is placed at an angle, it can either open or close on its own. This phenomenon occurs due to the transfer of energy from one form to another. Let's explore the reasons behind this and the energy involved.

1. Potential Energy and Gravity: When a door is placed at an angle, it gains potential energy due to its position relative to the ground. This potential energy is a result of the force of gravity acting on the door. The higher the angle, the greater the potential energy.

2. Kinetic Energy and Motion: If the door is released from its angled position, the potential energy is converted into kinetic energy as the door starts to move. As the door swings, the potential energy decreases while the kinetic energy increases. This conversion of energy allows the door to move.

3. Conservation of Energy: The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed from one form to another. In the case of the door, the potential energy is converted into kinetic energy, and vice versa. The total energy remains constant throughout the process.

4. Friction and Damping: The motion of the door may eventually slow down and come to a stop due to various factors such as friction and damping. Friction between the hinges and the door frame, as well as air resistance, can gradually reduce the kinetic energy of the door. Eventually, the door may stop moving and reach a state of equilibrium.

In conclusion, when a door placed at an angle either opens or closes on its own, it is due to the conversion of potential energy into kinetic energy. This process does not violate the law of conservation of energy, as the total energy remains constant throughout the motion of the door. Factors such as friction and damping may cause the door to eventually come to a stop.