Wikipedia describes the scientific view of kinetic energy as follows. “In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes”
The work-energy principle, we also learn, is that an increase in the kinetic energy of a body is caused by an equal amount of work done on the body by the force acting on it.
E = 1/2 mv2 is how we calculate kinetic energy. It is applicable when a steady force produces a steady acceleration on a mass M over a distance so that it achieves from a standstill a speed v. It is equally applicable in decelerating that mass steadily to rest. You can immediately see why it was thought that the accelerating energy must be acquired by the moving object and released in the deceleration process.
But what I cannot understand is why we still think this way. Do you really feel as if you have gained some energy when you are running and if so where do you think that energy has come from ? Does a 30 mph car engaging with a 90 mph train environment have more energy than when the same car at 30 mph. engages with a tree.
No wonder many scientists regard energy as a mathematical construct because that is precisely what we are making it into by saying a body has energy on account of its speed and then in gravity situations we allocate an object at height a higher potential energy than the same object at a lower level.
There is no force that accelerates an object at height toward the earth. There is a desire by the particles of the object for earth energies and that is what accelerates a free to do so object toward the earth. The object gathers speed but there is no force pulling it or pushing it toward the earth. There is no external energy driving its motion. The motion is born of particle energy desires for a more stable energy state. The structure will gain a little in mass energy as the earth emitted photons and air particles apply a motion restraining tiny upward force but insufficient to overcome the desire.
When the speeding structure nears the earth the influence of earth emitted energies on the falling structure rapidly increase and influence the motion of the structure decelerating its particles and accelerating them away in a vibrating pattern where mass energies gained are released as heat photons into the atmosphere as the object settles into a more repetitive vibrating state that we see as stability and which it prefers.
Though impossible to achieve two identical bodies travelling at different yet steady velocities through space and free from any external influence will have exactly the same particle mass energies and be exchanging the same photon energies. I repeat, there is no motion energy store. We are wrong to teach children there is and they grow into scientists who do the calculations and think there is a motion energy store.
Energy exchanges that act to separate structures will add to the mass energy of those structures. However that mass energy will increase significantly more for structures that cannot part easily than for structures that can part easily. The inner balls on a Newton’s cradle have their mass energies increased at the expense of motion.The outer balls gain little in mass energy because they are able to move away.