Concept
Velocity
Overview
Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector quantity, meaning that both magnitude and direction are needed to define it (velocity vector). The scalar absolute value (magnitude) of velocity is called speed, a quantity that is measured in metres per second (m/s or m⋅s−1) in the SI (International System of Units) system. For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object is said to be undergoing an acceleration.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Velocity is discussed.
This same velocity is that of the waves used in wireless telegraphy (which are like light waves, only longer) and in X-rays (which are like light waves, only shorter). It is generally held nowadays to be the velocity with which gravitation is propagated, though Eddington considers this not yet certain. (It used to be thought that gravitation was propagated instantaneously, but this view is now abandoned.)
Bertrand Russell, The A B C of Relativity
names the idea; a chapter is titled for it; states what it is; opens on it
If therefore the absolute velocity of the earth were straight and uniform, we should never have suspected the phenomenon of aberration; but it is variable; it is composed of two parts: the velocity of the solar system, which is straight and uniform; the velocity of the earth with reference to the sun, which is variable. If the velocity of the solar system, that is to say if the constant part existed alone, the…
Henri Poincaré, The Foundations of Science
names the idea; states what it is; opens on it
A direct analysis of the notion of velocity will bring us to the same conclusion. Mechanics gets this notion through a series of ideas, the connexion of which it is easy enough to trace. It first builds up the idea of uniform motion by picturing, on the one hand, the path AB of a certain moving body, and, on the other, a physical phenomenon which is repeated indefinitely under the same conditions,…
Henri Bergson, Time and Free Will
names the idea; states what it is; opens on it
The laws of sequence in physics, apart from quantum phenomena, are of two sorts, which appeared in traditional dynamics as laws of velocity and laws of acceleration. In a very short time, the velocity of a body alters very little, and if the time is taken short enough, the change of velocity diminishes without limit. This is what, in the last chapter, we called an “intrinsic” causal law. Then there is the effect of…
Bertrand Russell, Philosophy
names the idea; opens on it
We shall now see the consequences of admitting a velocity W > _c_. Let A and B be separated by distance _l_, and let velocity of a “signal” in the system S be W > _c_. Let the (observing) system S′ have velocity +_v_ with respect to the system S. Then velocity of signal with respect to system S′ is given by W′ = (W - _v_)/(1 - W_v_/_c²_) Thus “time” from A to B as measured in S′, is given by _l_/W′ = _l_(1 -…
Albert Einstein, The Principle of Relativity
names the idea; opens on it
Philosophers who discussed Velocity
Related ideas
- Kepler's laws of planetary motion
- Classical mechanics
- Momentum
- Motion
- Drag (physics)
- Second
- Special relativity
- Speed
- Calculus
- Newton's laws of motion
- Absolute value
Place in the tradition
Part of Deductive-nomological model.