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Why does accelerating near light speed take so much more energy?

Imagine adding energy to a spacecraft and getting ever smaller gains in speed. For an object with nonzero rest mass, special relativity predicts a steep rise in the energy needed as its speed approaches that of light. Explore where the familiar low-speed energy formula stops being a good approximation.

5–7 min

Questions you could explore

  • Where does the familiar low-speed kinetic-energy formula stop being a good approximation?
  • How does a graph of kinetic energy against speed differ from its low-speed approximation?

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