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Some of the most common examples of mechanical waves are water waves, sound waves, and seismic waves. Like all waves, mechanical waves transport energy. This energy propagates in the same direction as the wave. A wave requires an initial energy input; once this initial energy is added, the wave travels through the medium until all its energy is ...
The universe, as represented by the average motion of distant galaxies, does not appear to rotate relative to local inertial frames. Newton's gravitational constant G is a dynamical field. An isolated body in otherwise empty space has no inertia. Local inertial frames are affected by the cosmic motion and distribution of matter.
In any real situation, frictional forces and other non-conservative forces are present, but in many cases their effects on the system are so small that the principle of conservation of mechanical energy can be used as a fair approximation. Though energy cannot be created or destroyed, it can be converted to another form of energy. [1] [13]
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. [81] [82] Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms.
[5] [6] [7] Most examples of active matter are biological in origin and span all the scales of the living, from bacteria and self-organising bio-polymers such as microtubules and actin (both of which are part of the cytoskeleton of living cells), to schools of fish and flocks of birds.
According to the dominant cosmological model, the Lambda-CDM model, less than 5% of the universe's energy density is made up of the "matter" the Standard Model describes, and most of the universe is composed of dark matter and dark energy, with little agreement among scientists about what these are made of. [45]
In this definition, there is a critical pressure and an associated critical density, and when nuclear matter (made of protons and neutrons) is compressed beyond this density, the protons and neutrons dissociate into quarks, yielding quark matter (probably strange matter). The narrower meaning is quark matter that is more stable than nuclear matter.
This equation shows that the total energy of a particle (bradyon or tachyon) contains a contribution from its rest mass (the "rest mass–energy") and a contribution from its motion, the kinetic energy. When v is larger than c, the denominator in the equation for the energy is "imaginary", as the value under the radical is negative.