At very short time scales, however, the motion of a particle is dominated by its inertia and its displacement will be linearly dependent on time: Δ x = v Δ t. So the instantaneous velocity of the Brownian motion can be measured as v = Δ x /Δ t, when Δ t << τ, where τ is the momentum relaxation time. In 2010, the instantaneous velocity of a Brownian particle (a glass microsphere trapped in air with optical tweezers) was measured successfully. The velocity data verified the Maxwell–Boltzmann velocity distribution, and the equipartition theorem for a Brownian particle.