Various practical problems concerning the interaction and motion of bodies are solved using Newton's laws. However, the forces acting on the body can be very difficult to determine.
Then another important physical quantity, momentum, is used in the solution of the problem.
What is an impulse in physics?
Translated from the Latin "momentum" means"push". This physical quantity is also called the "amount of motion". It was introduced into science around the same time that the laws of Newton were discovered (at the end of the 17th century).
Section of physics, studying motion andThe interaction of material bodies, is mechanics. The impulse in mechanics is a vector quantity equal to the product of the body mass by its speed: p = mv. The directions of the momentum and velocity vectors always coincide.
In the SI system, a momentum of a body weighing 1 kg, which moves at a speed of 1 m / s, is taken as the pulse unit. Therefore, the pulse unit in SI is 1 kg? M / s.
In the computational problems, the projectionsVectors of velocity and momentum on an axis and use the equations for these projections: for example, if the x-axis is selected, then the projections v (x) and p (x) are considered. By the definition of momentum, these quantities are related by the relation: p (x) = mv (x).
Depending on which axis is chosen and where it is directed, the projection of the momentum vector on it can be either positive or negative.
Law of conservation of momentum
Impulses of material bodies with their physicalInteractions can vary. For example, when two balls hang suspended on threads, their impulses mutually change: one ball can come into motion from a stationary state or increase its speed, and the other, on the contrary, reduce the speed or stop. However, in a closed system, i.e. When the bodies interact only with each other and are not exposed to external forces, the vector sum of the impulses of these bodies remains constant for any of their interactions and motions. This is the law of conservation of momentum. Mathematically, it can be derived from Newton's laws.
The law of conservation of momentum is also applicable to suchSystems, where some external forces act on the bodies, but their vector sum is zero (for example, gravity is balanced by the force of the elasticity of the surface). Conditionally, such a system can also be considered closed.
In mathematical form, the law of conservation of momentumIs written as: p1 + p2 + ... + p (n) = p1 '+ p2' + ... + p (n) '(the momenta p are vectors). For a two-body system, this equation looks like p1 + p2 = p1 '+ p2', or m1v1 + m2v2 = m1v1 '+ m2v2'. For example, in the considered case with balls, the total momentum of both balls before the interaction will be equal to the total momentum after the interaction.