# Dictionary Definition

deceleration n : a decrease in speed; "the
deceleration of the arms race" [syn: slowing, retardation] [ant: acceleration]

# User Contributed Dictionary

## English

### Pronunciation

- /dɪˌsɛləˈɹeɪʃən/, /dI%sEl@"reIS@n/
- Rhymes: -eɪʃǝn

- The act or process of decelerating.
- The rocket is now in deceleration.

- The amount by which a speed or velocity decreases (and so a
scalar
quantity or a vector
quantity).
- The brakes produce a deceleration of 10 metres per second per second.

#### Antonyms

- (act, amount): acceleration

### Related terms

# Extensive Definition

In physics, acceleration is defined as the
rate of
change of velocity,
or as the second derivative of position (with
respect to time). It is then a vector
quantity with dimension length/time². In SI units, acceleration
is measured in
meters/second² (m·s-2). The term "acceleration" generally
refers to the rate of change in instantaneous velocity. (velocity
is speed and direction)

In common speech, the term acceleration is only
used for an increase in speed; a decrease in speed is called
deceleration. In physics, any increase or decrease in speed is
referred to as acceleration and similarly, motion in a circle at
constant speed is also an acceleration, since the direction
component of the velocity is changing. See also Newton's
Laws of Motion.

## Relation to relativity

After completing his theory of special relativity, Albert Einstein realized that forces felt by objects undergoing constant proper acceleration are indistinguishable from those in a gravitational field. This was the basis for his development of general relativity, a relativistic theory of gravity. This is also the basis for the popular Twin paradox, which asks why one twin ages less when moving away from his sibling at near light-speed and then returning, since the non-aging twin can say that it is the other twin that was moving. General relativity solved the "why does only one object feel accelerated?" problem which had plagued philosophers and scientists since Newton's time (and caused Newton to endorse absolute space). In special relativity, only inertial frames of reference (non-accelerated frames) can be used and are equivalent; general relativity considers all frames, even accelerated ones, to be equivalent. (The path from these considerations to the full theory of general relativity is traced in the Introduction to general relativity.)## Formula

The formula for the average acceleration over a time period \Delta t is- \mathbf=\frac

- \mathbf(t+\Delta t) is the final velocity
- \mathbf(t) is the initial velocity
- \mathbf is the initial time and \Delta \mathbf is the change in time

The formula for the instantaneous acceleration at
time t is

- \mathbf(t)=\lim_\frac=\frac

One should also note that the average and
instantaneous accelerations over a time period \Delta t=t_1-t_0 are
related through the Mean
Value Theorem for Integrals:

- \bar\int_^\mathrmt=\int_^\mathbf(t)\mathrmt

Putting it all together means:

- \mathbf = \frac = \frac

- \mathbf is acceleration
- \mathbf is velocity
- \mathbf is position
- is time

## See also

## External links

- Acceleration and Free Fall - a chapter from an online textbook
- Trajectories and Radius, Velocity, Acceleration on Project PHYSNET (ERROR - PAGE MOVED)
- Science aid: Movement
- Physics Classroom: Acceleration
- Science.dirbix: Acceleration
- Acceleration Calculator
- Motion Characteristics for Circular Motion

deceleration in Afrikaans: Versnelling

deceleration in Arabic: تسارع

deceleration in Asturian: Aceleración

deceleration in Bengali: ত্বরণ

deceleration in Min Nan: Ka-sok-tō͘

deceleration in Belarusian: Паскарэнне

deceleration in Bosnian: Ubrzanje

deceleration in Bulgarian: Ускорение

deceleration in Catalan: Acceleració

deceleration in Czech: Zrychlení

deceleration in Welsh: Cyflymiad

deceleration in Danish: Acceleration

deceleration in German: Beschleunigung

deceleration in Estonian: Kiirendus

deceleration in Modern Greek (1453-):
Επιτάχυνση

deceleration in Spanish: Aceleración

deceleration in Esperanto: Akcelo

deceleration in Basque: Azelerazio

deceleration in Persian: شتاب

deceleration in French: Accélération

deceleration in Irish: Luasghéarú

deceleration in Manx: Bieauaghey

deceleration in Galician: Aceleración

deceleration in Hakka Chinese: Kâ-suk-thu

deceleration in Korean: 가속도

deceleration in Croatian: Ubrzanje

deceleration in Ido: Acelero

deceleration in Indonesian: Percepatan

deceleration in Icelandic: Hröðun

deceleration in Italian: Accelerazione

deceleration in Hebrew: תאוצה

deceleration in Latin: Acceleratio

deceleration in Latvian: Paātrinājums

deceleration in Lithuanian: Pagreitis

deceleration in Hungarian: Gyorsulás

deceleration in Malayalam: ത്വരണം

deceleration in Malay (macrolanguage):
Pecutan

deceleration in Mongolian: Хурдатгал

deceleration in Dutch: Versnelling
(natuurkunde)

deceleration in Japanese: 加速度

deceleration in Norwegian: Akselerasjon

deceleration in Norwegian Nynorsk:
Akselerasjon

deceleration in Novial: Akseleratione

deceleration in Polish: Przyspieszenie

deceleration in Portuguese: Aceleração

deceleration in Quechua: P'ikwachiy

deceleration in Russian: Ускорение

deceleration in Sicilian: Accilirazzioni

deceleration in Simple English:
Acceleration

deceleration in Slovak: Zrýchlenie

deceleration in Slovenian: Pospešek

deceleration in Serbian: Убрзање

deceleration in Serbo-Croatian: Ubrzanje

deceleration in Finnish: Kiihtyvyys

deceleration in Swedish: Acceleration

deceleration in Telugu: త్వరణము

deceleration in Thai: ความเร่ง

deceleration in Vietnamese: Gia tốc

deceleration in Turkish: İvme

deceleration in Ukrainian: Прискорення

deceleration in Chinese: 加速度

# Synonyms, Antonyms and Related Words

arrest,
arrestation,
catabasis, check, collapse, constraint, control, cooling, cooling down, cooling
off, crash, curb, curtailment, declension, decline, decline and fall,
decrescendo,
delay, detention, diminuendo, dive, downtrend, downturn, drag, drop, dwindling, ease-off, ease-up,
ebb, fall, flagging, hindrance, holdup, inhibition, injunction, interdict, lag, lapse, legal restraint, letdown, letup, minus acceleration,
monopoly, obstruction, plunge, prohibition, protection, protectionism, protective
tariff, rationing,
rein, remission, restraint, restraint of trade,
retardation,
retardment, retreat, retrenchment, self-control,
setback, slack-up,
slackening, slowdown, slowing, slowing down, slowup, slump, subsidence, tariff wall,
thought control, wane