Momentum - The driving force
Any object that is moving has momentum. Momentum is the inclination of the object to keep moving in the same direction. It is difficult to change the direction of movement with an object with a lot of momentum. Momentum is calculated as part of the velocity group since it has speed and direction. They way we calculate momentum is;
p = m x v
P is the momentum in kilograms meters per second, kg m/s
m is the mass in kilograms, kg
v is velocity in m/s
Whereas speed is just a single scalar variable because velocity is active in this calculation the momentum of an object can change if the object speeds up or down or changes direction.
Newton's first law states that any object moving will continue moving unless it is interfered with. This law applies to momentum and if no external forces are acting on the object we state that the momentum is conserved. This means that if you threw a ball at a wall and it rebounds no kinetic energy is lost, the movement energy or momentum in this case. All the energy is still in the object and so we say that the energy has been conserved. If the kinetic energy didn't change, then neither did the value of momentum. This is because energy is scalar and because direction is part of vector grouping it doesn't effect the outcome. Now if you threw a brick at a wall the brick would bounce off but not as much as the ball and some of the energy would change. This is because the brick breaks which means heat, sound and kinetic energy are transferring from the object into other places such as the air and ground. This means that the energy was not conserved in the object but the total energy was, it's just split into different places.