Explain · Like I'm five version
Why the Tube is so hot in terms of a slow cooker
The London Underground is basically a giant, metal slow cooker that keeps everyone inside very warm.
The trains are the big, round lids that trap all the heat inside the tunnel. When the train moves, the wheels rub against the metal tracks and make a lot of friction. Friction is just a clever word for heat. Think of rubbing your hands together really fast until they feel warm. That is exactly what is happening under the floor of your carriage. It is like a soup made of people and hot air.
We are all the carrots and potatoes bubbling away in the stew. The tunnels are very old and deep, so the heat has nowhere to go. It just hangs around in the walls like a heavy winter blanket. The trains zoom back and forth, adding more heat every time they stop and start. It is a very busy kitchen where the chef has forgotten to ever turn the knob down from high.
You might think a big fan would help, but it just blows the warm air around in circles. The air stays stuck in the deep ground because it cannot climb out of the station. By the time you reach your stop, you are a very well-cooked little vegetable. You might even feel a bit like a soggy noodle after a long ride in the heat.
Where the analogy breaks downThe tube is not actually cooking the passengers into food.