Would the orit of planets be a good example of the law of conservation of energy?

Law: Energy can not be created or destroyed, but only change from one form to another.

Example: When satellites are in orbit, and the perihelion (closest point to the sun), they have the most kenetic energy. This is because the satellite must have enough intertia so its motion is not dominanted by the gravitational pull of the sun, which would pull the object in if its inertia was not great enough. As the object moves away from the perihelion and towards the aphelion (furthest point from the sun), it slows down. The kenetic energy is not lost, though. Instead, this energy is changed into potential energy. The orbital velocity of a satellite is cyclic, so therefore, the satellite has the most potential energy at the aphelion because it will increase in speed, and therefore in kenetic energy, as it gets closer to the perihelion.

Thank you for reading this. I am trying to study for a test and I wanted to see if my thoughts were correct. Any additional details I missed or is it good?


    • turboguppy on April 26, 2010 at 8:46 am
    • Reply
    You got it about right, but keep in mind that the path is a vector, the product of the object’s velocity and the pull of gravity. Orbits work because the speed of the object as it tries to escape balances the force holding it there. Think of a ball on a stretchy string, whirling over your head. The faster you whirl it, the further away from you it goes. This is the conservation of angular momentum.

    The object increases in speed as it approaches perihelioin because it is being pulled more by the sun’s gravity when it is closer, which adds speed along the vector of motion.

    I don’t know if that clarifies or muddies, but I think you had it about right.

    PS, I think conservation of energy has to do more with heat and thermodynamics, and what you are describing is the law of conservation of angular momentum.

    • Steve on April 26, 2010 at 9:34 am
    • Reply
    You have it exactly right. However, in most processes on earth, energy is seldom conserved due to friction, etc. An orbiting body in space experiences virtually no friction and can be considered an extremely close approximation of energy conservation.

    Momentum is conserved even when energy is not. This can be useful to figure velocities in energy dissipating situations.

    Spelling: Kinetic

Leave a Reply

Your email address will not be published.