Source:  SpeedSource Mazda With a Flame, Hunterrrr, Flickr

In the previous lesson we learned how to calculate momentum of a moving object.  Remember that momentum (p) is an object’s mass multiplied by its velocity.

p = mv

In this lesson, we will be looking at what happens when we apply a force to change an object’s momentum.  When a force is applied to an object over a length of time, scientists call it impulse.

Impulse is calculated by multiplying force times time interval.

Scroll over each variable in the equations below:

Putting these two definitions together gives us the impulse – momentum theorem:

F (Δt) = m (v_f – v_i)

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Here is the derivation of the equation.

Δp = p_f – p_i
Δp = mv_f – mv_i
Δp = m (v_f – v_i)
J    = m (v_f – v_i)
Since J is both F (Δt) and m (v_f – v_i), we get F (Δt) = m (v_f – v_i)