This is a big one! It is the Impulse-Momentum Relationship. It states that the net impulse delivered to an object is equal to the change in momentum of that object.

**Tip:** This is a *cause* equals *effect*
equation. The cause on the left is equal to the effect on the
right. When you use this equation, after first writing it down,
you should enter into substitution mode. On the left, substitute
the applicable net force-times-time-interval for the *J*;
on the right, substitute the final momentum minus the initial
momentum. Keep the cause on the left and the effect on the right
until you have boiled it down to an algebra problem which you can
then solve for the sought quantity.

**Tip:** The impulse in this equation is the net impulse. In the case of more than one
force acting on an object, the net impulse can be determined by
finding the net force and multiplying that by the time interval
during which it acts (see the definition of impulse),
or, the net impulse can be determined by finding the impulse due
to each force (again using the definition of impulse)
and adding all the impulses together like vectors.

**Pitfall Avoidance Note:** Both
impulse and momentum have direction. In problems involving motion
in one dimension, there are only two possible directions so you
can call one direction the positive direction and the other the
negative direction. Establish a positive direction and stick with
it throughout the problem on both sides of the equation.