All moving objects have momentum. Forces can cause changes in momentum. The total momentum in a collision or explosion is conserved and stays the same. Car safety features absorb energy involved in a crash they slow down the collision thus reducing the force of impact.
The period of a wave is the time it takes to complete one cycle. The unit for a wave period is seconds, and it is inversely proportional to the frequency of a wave, which is the number of cycles of a wave that occur in one second.
Speed is how fast an object is moving in no given direction. Velocity is how fast an object is moving in a given direction. In physics, you can calculate the average speed by taking the total distance travelled and dividing it by the total time required to travel that distance.