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Newton's first law expresses the principle of inertia: the natural behavior of a body is to move in a straight line at constant speed. A body's motion preserves the status quo, but external forces can perturb this. The modern understanding of Newton's first law is that no inertial observer is privileged over any other. The concept of an ...
There are two main descriptions of motion: dynamics and kinematics.Dynamics is general, since the momenta, forces and energy of the particles are taken into account. In this instance, sometimes the term dynamics refers to the differential equations that the system satisfies (e.g., Newton's second law or Euler–Lagrange equations), and sometimes to the solutions to those equations.
Newton’s Third Law of Motion (for every action there is an equal and opposite reaction) is also equivalent to the principle of conservation of momentum. Leibniz accepted the principle of conservation of momentum, but rejected the Cartesian version of it. [ 2 ]
The momentum of the object at time t is therefore p(t) = m(t)v(t). One might then try to invoke Newton's second law of motion by saying that the external force F on the object is related to its momentum p(t) by F = dp / dt , but this is incorrect, as is the related expression found by applying the product rule to d(mv) / dt : [17]
These fictitious forces are necessary for the formulation of correct equations of motion in a rotating reference frame [15] [16] and allow Newton's laws to be used in their normal form in such a frame (with one exception: the fictitious forces do not obey Newton's third law: they have no equal and opposite counterparts). [15]
Newton's Third Law is a result of applying symmetry to situations where forces can be attributed to the presence of different objects. The third law means that all forces are interactions between different bodies. [18] [19] and thus that there is no such thing as a unidirectional force or a force that acts on only one body.
Third law may refer to: Newton's third law of motion, one of Newton's laws of motion; Third law of thermodynamics; Kepler's Third law of planetary motion;
where m is the particle's rest mass, v its velocity, v is the modulus of v, and c is the speed of light. If v is very small compared to c, v 2 /c 2 is approximately zero, and so . Thus the Newtonian equation p = mv is an approximation of the relativistic equation for bodies moving with low speeds compared to the speed of light.