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Here we use the relativistic expression for linear momentum: =, where = / /. with being an object's (rest) mass, speed, and c the speed of light in vacuum. Then kinetic energy is the total relativistic energy minus the rest energy : E K = E − m 0 c 2 = ( p c ) 2 + ( m 0 c 2 ) 2 − m 0 c 2 {\displaystyle E_{K}=E-m_{0}c^{2}={\sqrt {(p{\textrm ...
[10] [11] Moreover, words which are synonymous in everyday speech are not so in physics: force is not the same as power or pressure, for example, and mass has a different meaning than weight. [12] [13]: 150 The physics concept of force makes quantitative the everyday idea of a push or a pull. Forces in Newtonian mechanics are often due to ...
The mass of an object as measured in its own frame of reference is called its rest mass or invariant mass and is sometimes written . If an object moves with velocity v {\displaystyle \mathbf {v} } in some other reference frame, the quantity m = γ ( v ) m 0 {\displaystyle m=\gamma (\mathbf {v} )m_{0}} is often called the object's "relativistic ...
In special relativity, an object that has nonzero rest mass cannot travel at the speed of light. As the object approaches the speed of light, the object's energy and momentum increase without bound. In the first years after 1905, following Lorentz and Einstein, the terms longitudinal and transverse mass were still in use.
In classical mechanics, for a body with constant mass, the (vector) acceleration of the body's center of mass is proportional to the net force vector (i.e. sum of all forces) acting on it (Newton's second law): = =, where F is the net force acting on the body, m is the mass of the body, and a is the center-of-mass acceleration.
At instant 1, a mass dm with velocity u is about to collide with the main body of mass m and velocity v. After a time dt, at instant 2, both particles move as one body with velocity v + dv. The following derivation is for a body that is gaining mass . A body of time-varying mass m moves at a velocity v at an initial time t.
The concept of momentum plays a fundamental role in explaining the behavior of variable-mass objects such as a rocket ejecting fuel or a star accreting gas. In analyzing such an object, one treats the object's mass as a function that varies with time: m(t). The momentum of the object at time t is therefore p(t) = m(t)v(t).
The speed of light in vacuum is thus the upper limit for speed for all physical systems. In addition, the speed of light is an invariant quantity: it has the same value, irrespective of the position or speed of the observer. This property makes the speed of light c a natural measurement unit for speed and a fundamental constant of nature.