When a system changes, energy moves between stores. To analyse a change, name the store that loses energy and the stores that gain it. When a ball is thrown upwards, its kinetic energy store decreases and its gravitational potential energy store increases. At the highest point it is momentarily at rest, so all of the kinetic energy has been transferred (ignoring air resistance). A 0.5 kg ball thrown up at 10 m/s starts with KE = ½ × 0.5 × 100 = 25 J. It gains 25 J of gravitational potential energy, and 25 = 0.5 × 10 × h gives a height of 5 m. An object moving up a slope does the same, except that friction also transfers some energy to the thermal store.
When a moving object hits an obstacle, its kinetic energy decreases to zero. The energy is transferred to other stores: the thermal stores of the object and the obstacle, sound waves, and an elastic store if either is squashed or bent.
Other changes follow the same pattern. An object accelerated by a constant force gains energy in its kinetic store, because the force does work on it. A vehicle slowing down transfers kinetic energy to the thermal store of its brakes by friction, and then to the surroundings. An electric kettle transfers energy from the electrical supply through the heating element to the thermal store of the water until it boils.