# State of motion

In mechanics, the movement state is the momentary movement of a body . This can consist of a translational and / or rotational movement .

• With regard to translational motion, the state of motion of a body is characterized by the speed of its center of mass with its current values ​​for magnitude and direction, i.e. in vector form. If the body gets faster or slower, or if it just changes the direction of its speed, its state of motion changes. The momentum is a quantitative measure of the translational state of motion .
• If the body rotates around its center of mass, this rotational movement is also part of its state of motion. The angular momentum is a measure of this part of the state of motion .

The uniform motion is an example of motion in which the state of motion remains unchanged. On the other hand, with a uniform circular motion of a body, the state of motion is not maintained, because here the direction of the speed is constantly changing.

The law of inertia or Newton's first law of mechanics says that every body that is not influenced by external forces remains in its state of motion. In other words, a body's striving to maintain its state of motion is an expression of its indolence . In particular, in the case of a body without external forces, the center of mass continues to move in a straight line at a constant speed. In the case of rotation around the center of mass, the angular momentum remains constant in terms of magnitude and direction, but not necessarily the axis of rotation and speed of rotation.

In the apparent contrast to the law of inertia, it is everyday experience that a moving body slows down precisely when no force can be determined to drive it. This is explained by the fact that braking forces such as air resistance and other friction forces are present with every movement . These are the cause of the deceleration of the body, i.e. the change in its state of motion. In general, Newton's second law of mechanics says how the state of motion changes when a resulting external force acts on the body.

## Individual evidence

1. Wolfgang Demtröder: Experimentalphysik 1: Mechanics and heat . Springer Berlin Heidelberg, July 2, 2013, ISBN 978-3-662-08598-1 , p. 51.
2. Ernst Grimsehl: Grimsehl textbook of physics: Volume 1 Mechanics · Acoustics · Heat theory . Vieweg + Teubner Verlag, April 17, 2013, ISBN 978-3-663-05732-1 , p. 27.
3. Wolfgang Demtröder: Experimentalphysik 1: Mechanics and heat . Springer Berlin Heidelberg, July 2, 2013, ISBN 978-3-662-08598-1 , p. 47.
4. Karsten Kirchgessner, Marco Schreck: Learning and Exercise Book for Theoretical Physics 1 .: Classical Mechanics . De Gruyter, November 27, 2013, ISBN 978-3-486-85842-6 , p. 2.