How can trains move on rails? if the wheels are smooth and the rails are also smooth, how can it be enough friction for it to move?
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Wait until you find out how an axle connected to it’s wheels can even turn. Kinda ingenious.
Wait until you find out how an axle connected to it’s wheels can even turn. Kinda ingenious.
Weight. Two pieces of ice can gain traction on each other with enough force pushing them together.
Weight. Two pieces of ice can gain traction on each other with enough force pushing them together.
The resulting movement between the wheel and the track is a function of both the force applied by the train on the track (ie. The weight of the train) and the coefficient of friction between the 2 surfaces. It is also a function of the size of the contact area between the 2 surfaces, however this doesn’t matter much in this discussion as I will clarify below.
As you mentioned, both surfaces are smooth metal surfaces, so the coefficient of friction is very low. That being said, the weight of the train is so massive, that even with this low coefficient of friction movement is achieved. Now that friction is achieved, we just need to ensure that the engine provides enough power to move the train in the horizontal direction.
The contact area between the wheel and the track can theoretically* also be increased if the weight of the train cant possibly increase enough (*this never applies in real life since the track is of constant size). This is however what many race cars must do, as they are looking to minimize weight.
The resulting movement between the wheel and the track is a function of both the force applied by the train on the track (ie. The weight of the train) and the coefficient of friction between the 2 surfaces. It is also a function of the size of the contact area between the 2 surfaces, however this doesn’t matter much in this discussion as I will clarify below.
As you mentioned, both surfaces are smooth metal surfaces, so the coefficient of friction is very low. That being said, the weight of the train is so massive, that even with this low coefficient of friction movement is achieved. Now that friction is achieved, we just need to ensure that the engine provides enough power to move the train in the horizontal direction.
The contact area between the wheel and the track can theoretically* also be increased if the weight of the train cant possibly increase enough (*this never applies in real life since the track is of constant size). This is however what many race cars must do, as they are looking to minimize weight.
There’s even less contact than you might think because the wheels are not flat to the rail, but rather are at an angle.
Each wheel tapers in slightly towards the center. It what keeps the wheels on the track and also allows the solid axle wheels to negotiate curves.
There’s even less contact than you might think because the wheels are not flat to the rail, but rather are at an angle.
Each wheel tapers in slightly towards the center. It what keeps the wheels on the track and also allows the solid axle wheels to negotiate curves.
The use of steel wheels on smooth steel tracks creates a very low rolling resistance – that is, the “braking” force that needs to be overcome to get a wheeled object to move. This low RR gives railway travel a very high efficiency.
Steel/steel friction is low but not zero. Trains are also very heavy, this weight somewhat improves the traction that can be applied. Trains therefore tend to accelerate (and decelerate) fairly slowly. For an electric train, if you’re not paying attention when the train sets off you will sometimes not realise you’re moving, at least for a few seconds.
The use of steel wheels on smooth steel tracks creates a very low rolling resistance – that is, the “braking” force that needs to be overcome to get a wheeled object to move. This low RR gives railway travel a very high efficiency.
Steel/steel friction is low but not zero. Trains are also very heavy, this weight somewhat improves the traction that can be applied. Trains therefore tend to accelerate (and decelerate) fairly slowly. For an electric train, if you’re not paying attention when the train sets off you will sometimes not realise you’re moving, at least for a few seconds.
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