# Train problem

1. Jun 29, 2009

### NAP2626

Hey I was hoping some would be able to help me or show me how to calculate the amount of force a train exerts on a spot on a track.

Simply I could calculate the force exerted on a spot of the track as the weight of the train in kgs times the gravity (9.8m/s^2) will give me netwons of force.

But... I want to know if trains are moving and also can I assume the whole weight of the train exerts on that point??

thanks for any help

2. Jun 29, 2009

### Staff: Mentor

You'll just need to divide by the number of wheels.

3. Jun 29, 2009

### maverick_starstrider

You need the weight of the train (its mass times g) divided by the total area that is making contact with the ground.

4. Jun 29, 2009

### NAP2626

ok, what about the moving portion or velocity of the train, will that alter the amount of force exterted down on the spot?

Ok by dividing by the number of wheels I can assume that fraction of the trains weight ( that amount of weight per wheel )is focused on that small spot?

Thanks guys for the help

5. Jun 29, 2009

### maverick_starstrider

well you can find the weight that each wheel must support, however that assumes a homogenous train. The velocity of the train would have no effect. It is directed in a direction perpindicular to gravity (assuming the train is on a flat track)

6. Jun 29, 2009

### Bob S

I think a freight car weighs about 130 tonnes (tonne-wt)= 1.275 x 10^6 Newtons (engines are heavier). This weight is supported by eight steel wheels, so the weight per wheel is about 1.59 x 10^5 Newtons. There are about 100 cars in a typical freight train, so there are about 400 wheels, each with this weight, rolling over every piece of track every time a freight train goes by. Suppose the total area under each wheel supporting the load is 10 cm^2 (guess). Then the compression pressure (stress) is 1.59 x 10^5 Newtons/.001 meters^2 = 159 megaPascals (MPa). This about the allowable compressive stress limit for steel.

Last edited: Jun 30, 2009
7. Jun 29, 2009

cool thanks