I think that the trip used to measure gas millage is a little downhill:
Let's start by assuming that the road is horizontal. All trips are made at the same speed (obviously).
At high speed the total energy needed for the trip is roughly the aerodynamic drag force time the distance traveled.
The energy to get going and the rolling resistance are small.
Under these hypothesis the trailer empty of full requires the same energy (gas) to move.
Still, you would expect the full trailer to burn a little more gas then the empty trailer (especially if the speed is slow).
But assume that the trip used to measure gas millage is a little downhill. The total energy needed is aerodynamic drag force time the distance traveled minus the altitude difference times the weight plus the rolling resistance coefficient times the weight times the distance traveled (*)
A small downhill can explain the data exactly: you just need altitude difference equal to rolling resistance coefficient times distance traveled...
(*) I am assuming a linear relationship between weight and rolling friction and that it's independent of speed... but other hypothesis will work.
I have quite an interesting problem that I cannot explain...
|
| Our Ag teacher set up this scenario for me:
|
| one 5000# truck gets about 18 miles per gallon same 5000#
| truck pulling a 4000# trailer gets 8 miles per gallon same
| 5000# truck pulling a 4000# trailer + 10000# of cows ALSO
| gets 8 miles per gallon.
|
| Any ideas why the empty and the full trailer both get the
| same mileage? This same pattern is also present in a
| different trailer and truck combination.
|
| thanks,
| Kathy