Why when the train races forward does its smoke go backwards?

Think of relying on coal and water yet still having sufficient energy to run over a hundred miles per hour – steam locomotives indeed are marvelous inventions. While they are no longer existing today and are replaced with more efficient trains on our railroads, steam locomotives undoubtedly left a mark in people’s heart and memory, and remain as attractions in most heritage railroads.

Steam locomotives were powered by steam engines, which is one of the most vital creations from the Industrial revolution. It was used in all kinds of applications, from mines, factories, steamboats, and the locomotives, and ranks with airplanes, cars, telephones, and television among the most significant inventions that changed the world. True enough, they are a wonder of engineering and machinery. But how do they work? Why is its smoke or steam go backwards even if the train races forward?

There are two types of steam engines, but both use a boiler in which water is heated to become steam. The first type of engine, high-pressure steam, is let out on a chamber. It expands and thrusts towards a moving piston. Whenever the steam is released, it forces the piston to go back to its initial position. The process repeats as the more steam is let out on the chamber. Meanwhile, the piston is connected to a specific part of the machine, and its movement causes the wheel to turn.

On the other hand, a steam turbine uses high-pressure steam and forces it to flow through stationary and moving blades. Thus, resulting in the rotor to move at fast speeds. Such movement produces a vast amount of electric power using steam.

Now, the ‘smoke’ that you see from the train is the exhausted steam from the boiling water and the smoke from the burning fuel, be it wood, coal, or burning fuel. But, why does the smoke go backwards when the train races forward?

First, let’s remember that smoke is hot air and lighter, which is why it goes up. Smoke being less dense, allows a buoyant force upwards due to it having a pressure gradient brought by gravity. Then, let’s go into Newton’s Law of Motion that states that if an object doesn’t experience any net force, then it will remain constant or stagnant. Whenever there is no force, no one will keep it moving. That is why an object stays at rest when there is an absence of force. Such as train smoke seemingly goes upwards on a quite straight upward line when it is at the station.

Now, what makes the difference? It’s force. As the train goes forward, it pushes vast amounts of air along its way. What happens is that it creates an air resistance force or the force that enacts in opposition to the motion of an object as it passes or travels through the air. However, since smoke tends to be much lighter, it experiences air resistance. Thus, causing it to move backwards or in the opposing direction. Smoke from the train will move along the train at the same speed if there is no air to create resistance force, such as a vacuum.

More Readings:

Steam Locomotives (Wikipedia)

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