# B Torsion, helicity of drive shaft, direction of energy-flow.

#### Spinnor

Gold Member
The drive shaft of a truck undergoing acceleration twists a small amount. That twist defines a helicity. If you just know the rotation of a drive shaft you can not tell which way power flows but if given rotation and the twist of the shaft that can determine the direction of power flow?

Thanks!

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#### A.T.

The drive shaft of a truck undergoing acceleration twists a small amount. That twist defines a helicity. If you just know the rotation of a drive shaft you can not tell which way power flows but if given rotation and the twist of the shaft that can determine the direction of power flow?
Yes.

#### Spinnor

Gold Member
That is cool.

Energy can flow in both directions of a trucks drive shaft but energy normally flows towards the wheels but when a truck uses its air-brakes (edit, or just lets off the gas) to slow down energy flows towards the engine?

Edit, to recover energy from a car or truck energy must flow the other direction.

Thanks!

"Torsion, helicity of drive shaft, direction of energy-flow."

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