Vertical component of the velocity of the centre of gravity of the penguin.
The figure shows the vertical component of the velocity of the centre of gravity of the penguin v(t), calculated using the first approximation (6). Any velocity trend (slope) indicates the weight estimate is in error. The slope of the linear regression (also shown) gives the relative error of the first approximation (8). Thus we calculate the second approximation of the penguin weight (10).