Here's why:
* Energy Production: Coal is a fossil fuel that releases a lot of heat when burned, which is necessary to produce steam.
* Historical Significance: Coal was the most readily available and affordable fuel during the peak of steam train use in the 19th and early 20th centuries.
* Other Options: While coal was the primary fuel, some steam trains have used wood, oil, or even a combination of fuels depending on availability and cost.
It's important to note that modern steam trains are becoming increasingly rare, and many have transitioned to more environmentally friendly fuels or even electric power.
