This demonstration allows you to add velocities using the three-dimensional relativistic combination law. Use the first three sliders to select the velocity of an object in the ‘stationary’ frame. Use the last slider to choose the velocity of the ‘moving’ frame relative to the ‘stationary’ frame. The demonstration illustrates and calculates the velocity of the object from the perspective of the ‘moving’ frame. Notice that all components of the velocity of the object are affected, even if those components are orthogonal to the relative velocity between the two frames.