In physics, Torricelli's equation, or Torricelli's formula, is an equation created by Evangelista Torricelli to find the final velocity of a moving object with constant acceleration along an axis (for example, the x axis) without having a known time interval.
The equation itself is:[1] where In this and all subsequent equations in this article, the subscript
) is implied, but is not expressed explicitly for clarity in presenting the equations.
This equation is valid along any axis on which the acceleration is constant.
Begin with the following relations for the case of uniform acceleration: Take (1), and multiply both sides with acceleration
The following rearrangement of the right hand side makes it easier to recognize the coming substitution: Use (2) to substitute the product
: Work out the multiplications: The crossterms
drop away against each other, leaving only squared terms: (7) rearranges to the form of Torricelli's equation as presented at the start of the article: Begin with the definitions of velocity as the derivative of the position, and acceleration as the derivative of the velocity: Set up integration from initial position
to final position
In accordance with (9) we can substitute
{\textstyle v\,dt}
, with corresponding change of limits.
Here changing the order of
makes it easier to recognize the upcoming substitution.
In accordance with (10) we can substitute
, with corresponding change of limits.
Since the acceleration is constant, we can factor it out of the integration: Evaluating the integration: The factor
: Combining Torricelli's equation with
gives the work-energy theorem.
Torricelli's equation and the generalization to non-uniform acceleration have the same form: Repeat of (16): Evaluating the right hand side: To compare with Torricelli's equation: repeat of (7): To derive the work-energy theorem: start with
and on both sides state the integral with respect to the position coordinate.
If both sides are integrable then the resulting expression is valid: Use (22) to process the right hand side:
The reason that the right hand sides of (22) and (23) are the same: First consider the case with two consecutive stages of different uniform acceleration, first from
Expressions for each of the two stages:
Since these expressions are for consecutive intervals they can be added; the result is a valid expression.
Upon addition the intermediate term
drops out; only the outer terms
remain: The above result generalizes: the total distance can be subdivided into any number of subdivisions; after adding everything together only the outer terms remain; all of the intermediate terms drop out.
The generalization of (26) to an arbitrary number of subdivisions of the total interval from
can be expressed as a summation: