Animated Solution for Physics - Work, Energy, and Power: If a machine is lubricated with oil,

To truly appreciate this problem, we must first understand what a machine is in the realm of physics. A machine is not necessarily a complex engine with gears and motors; it can be as simple as an inclined plane, a lever, or a pulley. The fundamental purpose of any machine is to transmit or modify force to perform work.

Imagine you are trying to lift a heavy block. Doing it directly against gravity might require more force than you can muster. By using an inclined plane, you can apply a smaller pulling force, known as the Effort ($E$), to move the heavy block, known as the Load ($L$), over a longer distance.

Friction

In an ideal, textbook universe, every single joule of energy you put into the machine (the Input Work) would be perfectly converted into useful work done on the load (the Output Work). However, the real world is governed by thermodynamics and microscopic imperfections.

As the block slides up the inclined plane, the rough surfaces grind against each other. This interaction gives rise to kinetic friction, an invisible thief that constantly opposes the motion. Because of this friction, a significant portion of your hard-earned Input Work is dissipated into the environment as useless heat energy.

We can express this reality mathematically:

This brings us to the core of the problem: lubrication. When we apply oil to the machine, we are introducing a viscous fluid layer between the solid surfaces. This fluid layer physically separates the microscopic peaks and valleys of the block and the plane.

Instead of harsh solid-to-solid grinding, the surfaces now glide over each other with fluid friction, which is drastically lower than kinetic friction. By lubricating the machine, we effectively minimize the friction force ($f$), which in turn minimizes the work wasted against friction ($W_{\text{friction}}$).

Mechanical Advantage

To evaluate a machine's performance, we use two distinct metrics: Mechanical Efficiency ($\eta$) and Mechanical Advantage ($MA$).

Efficiency is the ratio of useful energy out to total energy in:

Since lubrication reduces the wasted work, the Input Work required to achieve the same Output Work decreases. A smaller denominator means the overall fraction increases. Therefore, the efficiency unambiguously increases.

But what about Mechanical Advantage? It is defined as the ratio of the load to the effort:

There is also the Velocity Ratio ($VR$), which is the ratio of the distance moved by the effort to the distance moved by the load. These three are connected by a beautiful relation:

Here lies the classic trap. While the Actual Mechanical Advantage does increase (because you need less effort to lift the same load), the term "Mechanical Advantage" in many classical physics contexts refers to the Ideal Mechanical Advantage (IMA).

The IMA is purely a geometric property of the machine, identical to the Velocity Ratio. Since adding oil does not change the physical dimensions or shape of the inclined plane, the Ideal Mechanical Advantage remains perfectly constant.

Because "Mechanical Advantage" can be ambiguous (referring to either Actual or Ideal), but "Efficiency" is strictly and universally tied to energy losses, the most accurate and universally accepted answer is that only the mechanical efficiency increases.

Thus, option (b) is the correct choice.