It takes more energy to accelerate a tennis ball to 80% of the speed of light (0.8c) than it takes to accelerate an electron to 80% the speed of light. It takes

It takes more energy to accelerate a tennis ball to 80% of the speed of light (0.8c) than it takes to accelerate an electron to 80% the speed of light. It takes more energy to accelerate a tennis ball to 0.999c than an electron to 0.999c. But the faster and faster you go, the more energy is required. As the number approaches 100%, the energy required for each tiny fractional step goes up exponentially, so much so that it is impossible to accelerate either object to 100% of the speed of light. It just requires more, and more, and more energy.