If I lift a weight to a certain height, where does the gravitational potential energy at that height originate from?
is kinetic energy converted into gravitational potential energy as the weight is decelarating as it approaches the maximum height? or is the chemical energy from my body (doing the work) shared between kinetic energy and gravitational potential energy?
Hope this makes sense. thanks.
Initially when you push an object from rest to a certain height, you do have to make the object initially accelerate so some of that energy is used towards kinetic energy atleast momentarily and the normal force(applied force) is temporarily greater than the gravitational force down. However after that, whether the energy is used for more kinetic energy and gravitational potential energy, or just gravitational potential energy depends on whether the block is accelerating up or going at a constant velocity up.
If the block is accelerating up, then it means that you are applying net work on the object because there is a force up and a displacement up, so the kinetic energy increases and the potential increases because some of the energy is used to place the block higher up.
If the block is going at a constant velocity, the energy provided goes into increasing just the height.
So basically the chemical energy turns into potential energy always, but can additionally turn into kinetic energy if the block is accelerating up.
If I lift a weight to a certain height, where does the gravitational potential energy at that height originate from?
It originates from the chemical potential energy stored in the cells of your body. That energy is converted to kinetic energy when you perform positive work on the weight when you lift it. At the same time you do positive work on the weight transferring energy to it, gravity is doing negative work on the weight taking energy away from it (the work of gravity is negative because the force of gravity is in the opposite direction of the displacement of the weight).
If the weight begins at rest before you lift it and ends at rest at a height of $h$ then its overall change in kinetic energy is zero. From the work energy theorem that means the positive work you do on the weight of $mgh$ equals the negative work done by gravity of $-mgh$, for a net work of zero. This occurs if initially your upward force is greater than gravity accelerating the weight giving it kinetic energy. Then prior to reaching the final height you reduce your force to less than gravity decelerating the weight taking away the initial kinetic energy bringing it to rest.
Finally, the energy $mgh$ taken from the weight by the negative work done by gravity is stored as gravitational potential energy of $mgh$ in the earth-weight system.
Hope this helps.
