Effective mass (solid-state physics) from both sides gives where is the th element of , is the th element of , and are the th and th elements of , respectively, and is the total energy of the particle according to the Planck–Einstein relation. The index is contracted by the use of Einstein notation (there is an implicit summation over ). Since Newton's second law uses the inertial mass (not the gravitational mass), we can identify the inverse of this mass in the equation above as the tensor This tensor expresses the change in group velocity due to a change in crystal momentum. Its
Wheelie to mass times acceleration, then the minimum power required for a wheelie can be expressed as the product of mass, velocity, and the minimum acceleration required for a wheelie: Thus the minimum power required is directly proportional to the mass of the vehicle and to its velocity. The slower a vehicle is moving, the less power is required to perform a wheelie, and that is without even considering the power required to overcome air drag, which increases with the cube of velocity. Therefore, the least amount of power required is when the vehicle begins accelerating from rest. In the case