Hello!!! This has always confused me since I was a kid.
How exactly do modern cars, or older steam locomotives, move when they have multiple tons of metal sitting on top of them? Like how does all of that mass sit on an axel and the axel is still able to rotate at high speeds? I’ve seen train axels/wheels in person and it’s basically a large metal rod with a wheel on each end. Does the force of the engine overcome the friction of all of that weight?
Thank you in advance!
For anyone else who is curious about this in the future, several of the comments below were super helpful. I was also able to find this video on YouTube as a visual demonstration based on the leads these guys provided!
https://youtu.be/lIEHscqWJAk
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Wheels make that slap of metal move like butter, ofc it will also require considerable amount of torque (spinning power) to move the wheels.
A normal car engine produces around 200 horse powers and a normal car weights around 2 tonnes. So imagine 200 horses pulling 2 tonnes of weight on wheels.
While the axle weights a lot, most of the weigh is in the engine bay. The axle is a very simple mechanism with a few gears designed to rotate at high speed. The purpose of the axel is to distribute torque to all the wheels and to operate as an Anti brake system, a system to distribute torque differently when you turn. Lets say you are turning right, the axle will deliver less torque to the driver side and more to the off side. This way the wheels wont slip even if there are pot holes. And also pot holes and films of water on the road, it does similar things.
Trains weights alot more so it would be logical to gives it a bigger engine.
Trains and cars both have enormous motors called Drives, that have to be powered by either combustion engines, what you see in cars, by basically controlled explosions of fuel, or with trains they simply need a lot of energy in the motors in order to make them spin. On top of that, trains’ weight actually helps them stick to the track by making it extremely hard to move the wheels unless everything on top of them is moving as well because of the incredible force pushing the contact point down into the track. Hope this was helpful. If you still have a question, please ask.
The friction is very low when you rub polished steel against polished steel. Trains just need to overcome inertia to get moving. That is why they don’t accelerate very fast or stop very fast. The way locomotives can get more friction by spraying sand down by the steel wheels to create friction between the wheel and the tracks.
they only need enough power to overcome friction and wind resistance. you might be surprised how little power cars actually need just to move.
>does all of that mass sit on an axel and the axel is still able to rotate at high speeds?
this is exactly what happens. the weight is loaded on springs to give a more comfortable ride, but the axles do the work.
Axels can spin easily despite all the weight on them because they use bearings. If you’ve played with a fidget spinner then you’ve played with a bearing before. They allow the axle to rotate without any rubbing so the friction is extremely low. The way the bearings work is by having little steel balls sit between the axle and the rest of the car. These balls will roll around as the axle spins, always keeping the axle from rubbing against anything. This allows the car to roll fairly easily despite how heavy it is.
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It’s the magic of bearings. What you don’t see from outside is that all that weight rests on rollers, it’s not just an axle and wheels, there are roller bearings holding all that weight. Rolling resistance is small, provided you can get it moving to begin with pushing a train cart around takes very little power. Here are passengers pushing an entire train https://www.railtech.com/all/2022/05/19/ukrainian-passengers-push-6-train-cars-after-losing-electrical-contact/?gdpr=accept
They have enough torque to move the object in question
Torque is the measure of rotational force being exerted by the engine/motor normally measured in foot pounds
1 foot pound of torque is equal to one pound of force being exerted on an object from one foot away
Modern v8’s can easily have 400+ foot pounds of torque which is more than enough torque to move a considerable amount of weight, like 15,000+ lbs
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