The law of conservation of momentum is a common law of physics, in which the quantity is called momentum, that characterizes motion never changing in an isolated collection of objects, finalizing that the total momentum of a system remains constant. The term constant is used to define something that doesn’t change, more specifically when there is no change before and after an event. Therefore, conservation of momentum is directly defined as momentum is unchanged before and after an event.
There are many conserved quantities in physics, usually used for making predictions in hypothetical, complex situations that are usually too complicated. Some examples are angular momentum, energy, and momentum, where momentum refers to collisions between objects. However, conservation of momentum only applies to an isolated system of objects. In this specific law, an isolated system is when there is no external force acting on the objects. What this means specifically is that you must include both objects, any forces acting on the objects, and the amount of time for the system.
Many may be asking, “now we know what the meaning of this law is, but why is momentum conserved”? Momentum is conserved because it is directly related to Newton’s third law, which states that every action in nature has a reaction of equal proportions but in the opposite direction. A more specific example would be if you take object A and B and have them collide, there is a force by object A on object B, but because of what Newton’s third law states, there is also an equal force by object B on object A, but in the opposite direction. The forces act on each other once they make contact in the collision. The time it takes for the collision will be different based on the situations such as two softer and squishier objects compared to harder and more solid objects, but the time of each object in the collision has to be the same for each object. As a result, the impulse of the objects must be equal in magnitude but opposite in direction. Impulse is also known as the change in momentum, therefore, according to the law of conservation of momentum, impulse has to equal zero for momentum to be considered conserved in a system.
Momentum is a vector quantity, which means that we use vector addition to sum together the momentum of multiple bodies making up a system. Specifically, in a system with two objects that have equal speed and opposite direction, the two objects’ momentum would cancel out because although the two objects are moving, the opposite directions result in the momentum of the system being zero. Measuring momentum, even in complex situations, is quite easy. An example would be two objects that collide so forcefully that it breaks one of the objects. It is easy to see that although the kinetic energy of the object is not conserved, the momentum is because the shards of the object go flying out with the same momentum.
In conclusion, the law of conservation of momentum is a common law used in physics to describe a collision between two objects, such that momentum is unchanged before and after the collision. The momentum is only conserved if the collision is in an isolated system. Momentum is conserved due to Newton’s third law. Momentum is an interesting law that is seen in most of our everyday lives.
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By: Zubin Sidhu
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References:
“What Is Conservation of Momentum?” Khan Academy, www.khanacademy.org/science/high-school-physics/linear-momentum-and-collisions/elastic-collisions-and-conservation-of-momentum/a/what-is-conservation-of-momentum. Accessed 27 Mar. 2021.
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