Tractive effort facts for kids

Tractive effort, also known as tractive force, is a term used in railway engineering. It describes the total pulling power of a locomotive or train. Think of it as the strength a train has to pull itself and all its wagons along the tracks.

What is Tractive Effort?

Tractive effort is the force that moves a train forward. It's the power that makes the wheels turn and grip the rails, pushing the train down the track. Without enough tractive effort, a train wouldn't be able to start moving or pull heavy loads.

How Trains Get Their Pulling Power

Trains create tractive effort using their engines and wheels. The engine generates power, which is then sent to the wheels.

Engines and Wheels

Inside a locomotive, a powerful engine (like a diesel engine or an electric motor) creates energy. This energy is then transferred to the train's wheels. As the wheels spin, they push against the railway track. This pushing action is what moves the train.

The Role of Friction

For the wheels to push the train forward, they need grip. This grip comes from friction between the wheels and the rails. Imagine trying to run on ice – it's hard because there's not much friction. Trains need a lot of friction to get enough tractive effort. If the wheels spin without gripping, it's called "slipping."

Why Tractive Effort Matters

Tractive effort is super important for several reasons. It affects how fast a train can go, how much it can carry, and how easily it can start and stop.

Starting and Stopping

When a train needs to start moving from a standstill, it needs a lot of tractive effort. This initial push helps overcome the train's weight and the resistance of the tracks. Similarly, tractive effort is used to control the train's speed and help it slow down or stop.

Pulling Heavy Loads

One of the main jobs of a train is to pull many wagons, often filled with heavy goods. The more wagons and the heavier the cargo, the more tractive effort the locomotive needs. A powerful locomotive with high tractive effort can pull very long and heavy trains.

Factors Affecting Tractive Effort

Several things can influence how much tractive effort a train can produce. These include the locomotive's weight, how well its wheels grip the rails, and the power of its engine.

Locomotive Weight

The weight of the locomotive itself helps with tractive effort. A heavier locomotive can press its wheels down onto the rails more firmly. This increases the friction, allowing the wheels to get a better grip and produce more pulling power.

Adhesion and Slipping

Adhesion is the term for the grip between the wheels and the rails. Good adhesion means the wheels won't slip. Things like wet rails, leaves on the track, or even a little bit of oil can reduce adhesion. When adhesion is low, the wheels might spin without moving the train, reducing the effective tractive effort. Trains sometimes use sand to improve adhesion on slippery tracks.

Engine Power

The power of the locomotive's engine directly affects its tractive effort. A more powerful engine can generate more force to turn the wheels. This means it can produce greater pulling power, allowing the train to pull heavier loads or accelerate faster.

Images for kids

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  Diagram of tractive effort versus speed for a hypothetical locomotive with power at rail of ~7000 kW