Learner's definition of MOMENTUM
1 a : the strength or force that something has when it is moving b : 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.
2 physics : the property that a moving object has due to its mass and its motion