Light travelling in a vacuum is the fastest thing in the universe. The speed would be 2.99x10^8 m/s. The answer to this question is 'vacuum', where light can travel the fastest. I hope this helps you. You're welcome!
Answer:
acceleration
Explanation:
The rate at which velocity changes is the definition of the physical quantity called acceleration, and it is given by the formula: 
where
is the time that took to change from the initial velocity
to the final velocity 