Verb tense places an event in the present, the past, or the future.
As an object approaches the speed of light, its mass rises.
In 1887, Albert Michelson and Edward Morley compared the speed of light in the direction of the earth's motion with that at right angles to the earth's motion.
--Stephen Hawking, A Brief History of Time
We will calculate our results to the nearest tenth.
See also Present Perfect Tense, Past Perfect Tense, and Future Perfect Tense.