Slowing down and lowering involve energy removal (-W), while lifting and falling require energy addition (+W) against or with gravity.
In the realm of physics, the exchange of energy occurs through various processes, with work being done on or by an object. Let's explore the energy interactions in the given scenarios.
Slowing down an object
When slowing down an object, external forces (e.g., friction) act against its motion. In this case, energy is removed (-W) from the object. The kinetic energy of the object is transformed into other forms of energy, such as heat, as it decelerates.
Lifting an object into the air:
Lifting an object against the force of gravity requires the input of energy. In this scenario, energy is added (+W) to the object. The work done is against gravity, resulting in potential energy being stored in the lifted object.
Lowering an object to the ground slowly:
When lowering an object gradually, gravity assists the motion. Here, energy is removed (-W) from the object, but it is dissipated as potential energy is converted back into kinetic energy. The work done by gravity is negative, but the object gains kinetic energy as it descends.
An object falling:
As an object falls, gravity accelerates it, increasing its kinetic energy. In this case, energy is added (+W) to the object. The work done by gravity is positive, transforming potential energy into kinetic energy.
In summary, slowing down an object and lowering it to the ground both involve the removal of energy (-W), while lifting an object and an object falling both require the addition of energy (+W) to overcome gravitational forces.