Learner's definition of MOMENTUM
the strength or force that something has when it is moving
the strength or force that allows something to continue or to grow stronger or faster as time passes
The company has had a successful year and hopes to maintain its momentum by introducing new products.
The campaign slowly gained/gathered momentum. [=the campaign slowly became more popular and successful]
The movie loses momentum toward the end.
the property that a moving object has due to its mass and its motion