According to special relativity, the relativistic mass of a moving object increases with velocity: \(m = \frac{m_0}{\sqrt{1-v^2/c^2}}\), where \(m_0\) is the rest mass. As \(v \to c\), \(m \to \infty\). This relativistic mass increase is observed experimentally in particle accelerators and explains why massive objects cannot reach the speed of light.