im·pe·tus 
(ĭmpĭ-təs)
(ĭmpĭ-təs)n. pl. im·pe·tus·es
1. An impelling force; an impulse.
2. The force or energy associated with a moving body.
3.
a. Something that incites; a stimulus.
b. Increased activity in response to a stimulus: The approaching deadline gave impetus to the investigation.
[Middle English impetous, from Latin impetus, from impetere, to attack : in-, against; see IN-2 + petere, to go towards, seek; see pet- in the Appendix of Indo-European roots.]