When an object is dropped from a tower, what is the effect of the air resistance as it falls? 1) does positive work 2) increases the object's kinetic energy 3) increases the object's potential energy 4) increases the total energy of the object 5) None of the above choices are valid.

When an object falls, gravity converts its potential energy into kinetic energy. Air resistance, however, opposes the motion of the object, performing negative work (meaning it takes away energy). This negative work reduces the kinetic energy that would have been gained if the object were in free fall, and it also reduces the total mechanical energy of the system. Now, let’s examine the choices: 1) Does positive work – Incorrect, because air resistance does negative work. 2) Increases the object's kinetic energy – Incorrect, because air resistance slows the object down, reducing its kinetic energy. 3) Increases the object's potential energy – Incorrect, because potential energy is decreasing as the object falls. 4) Increases the total energy of the object – Incorrect, because air resistance removes energy from the system. 5) None of the above choices are valid – This is the correct answer. Thus, the effect of air resistance as the object falls is not described by any of the above choices, so the correct answer is: 5) None of the above choices are valid.