According to Einstein's theory of special relativity, as an object with mass approaches the speed of light, its mass effectively becomes infinite. This means that the closer an object with mass gets to the speed of light, the more difficult it becomes to accelerate it further, as its mass increases without bound.
The equation that describes this phenomenon is:
m=m01−v2c2,m = dfrac{m_0}{sqrt{1 - dfrac{v^2}{c^2}}},m=1−c2v2m0,
where: mmm = relativistic mass of the object at velocity vvv, m0m_0m0 = rest mass of the object (mass when at rest), vvv = velocity of the object, and ccc = speed of light in a vacuum.
As vvv approaches ccc (the speed of light), the denominator 1−v2c2sqrt{1 - dfrac{v^2}{c^2}}1−c2v2</s