# Speed vs. Fast — What's the Difference?

By Tayyaba Rehman & Urooj Arif — Updated on March 30, 2024
Speed refers to the rate at which something moves, measured in units, while fast describes a high speed or quickness of action or movement.

## Key Differences

Speed and fast are terms often used interchangeably in casual conversation, but they have distinct meanings, especially in scientific contexts. Speed is a scalar quantity that refers to how fast an object is moving along a path. It is typically measured in units such as miles per hour (mph) or kilometers per hour (kph). Fast, on the other hand, is an adjective that qualitatively describes the rapidity of movement or action. While speed provides a quantitative measure, fast offers a qualitative assessment, indicating that something is moving or being done with great velocity or quickness.
When discussing the movement of an object, speed provides a specific numerical value to describe the rate of motion, such as "60 mph." Fast, however, is used to describe the general nature of the movement without specifying the rate, as in "The car is moving fast." This distinction is crucial in contexts where precision is important, such as scientific research, engineering, and sports analytics, where speed measurements are essential for accurate calculations and assessments.
In physics, speed is an integral concept that helps quantify motion. It is the magnitude of velocity, disregarding its direction. Fast, however, does not fit into the language of physics as a measurable quantity but rather serves as a descriptor in everyday language to compare the relative speeds of objects or the quickness of actions, such as "faster than a speeding bullet."
The perception of what constitutes "fast" can vary greatly depending on the context. For example, a car moving at 60 mph is considered fast to a pedestrian but relatively slow on a highway where the average speed is higher. Similarly, in the realm of internet connectivity, what is considered a fast connection speed can change as technology advances and higher bandwidths become standard. This subjective nature of fast highlights its role as a comparative rather than an absolute measure.
Both terms are applied beyond physical movement to describe rates of change or activity in various fields. For example, in computing, one might refer to the speed of a processor in terms of gigahertz (GHz), while describing a software program as "fast" in terms of its performance or responsiveness. This demonstrates how the concepts of speed and fast permeate different domains, each term chosen for its relevance to the context.

## Comparison Chart

### Definition

The rate of motion or action, quantifiable and measured in units
Qualitatively describes rapid movement or action, without specific measurement

### Context

Used in scientific, technical, and precise discussions
Used in everyday language, comparisons, and qualitative assessments

### Measurement

Yes, with units like mph, kph, m/s
No, subjective and relative

### Example Usage

"The speed of the car is 60 mph."
"The car is moving fast."

### Application

Quantifying motion, calculating distances and times
Describing quickness, efficiency, or preference for speed

## Compare with Definitions

#### Speed

Rate of motion.
The speed of light is approximately 299,792 kilometers per second.

#### Fast

Quickness of movement.
Cheetahs are known for their fast running speed.

#### Speed

Measured in units.
Speed limits on highways are often set at 70 mph.

#### Fast

Used in comparative assessments.
Fiber-optic connections are faster than DSL.

#### Speed

Scalar quantity in physics.
Speed is independent of direction.

#### Fast

Describes efficiency or preference.
He prefers fast cars.

#### Speed

Used in precise calculations.
The speed of a processor is measured in GHz.

#### Fast

Rapid action or performance.
Fast response times are essential in emergency services.

#### Speed

Quantitative aspect of motion.
The speed of an internet connection is crucial for streaming.

#### Fast

Lacking specific measurement.
He is known for eating fast.

#### Speed

In everyday use and in kinematics, the speed (commonly referred to as v) of an object is the magnitude of the rate of change of its position with time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero.

#### Fast

Acting, moving, or capable of acting or moving quickly; swift.

#### Speed

The rate at which someone or something moves or operates or is able to move or operate
We turned on to the runway and began to gather speed
The car has a top speed of 147 mph
An engine running at full speed

#### Fast

Accomplished in relatively little time
A fast visit.

#### Speed

Each of the possible gear ratios of a bicycle.

#### Fast

Acquired quickly with little effort and sometimes unscrupulously
Made a fast buck scalping tickets.

#### Speed

The light-gathering power or f-number of a camera lens.

#### Fast

Quick to understand or learn; mentally agile
A class for the faster students.

#### Speed

An amphetamine drug, especially methamphetamine.

#### Fast

Indicating a time somewhat ahead of the actual time
The clock is fast.

#### Speed

Success; prosperity
Wish me good speed

#### Fast

Allowing rapid movement or action
A fast running track.

#### Speed

Move quickly
I got into the car and home we sped

#### Fast

Designed for or compatible with a short exposure time
Fast film.

#### Speed

Make prosperous or successful
May God speed you

#### Fast

Disposed to dissipation; wild
Ran with a fast crowd.

#### Speed

Take or be under the influence of an amphetamine drug
More kids than ever are speeding, tripping, and getting stoned

#### Fast

Resistant, as to destruction or fading
Fast colors.

#### Speed

Distance traveled divided by the time of travel.

#### Fast

Firmly fixed or fastened
A fast grip.

#### Speed

The limit of this quotient as the time of travel becomes vanishingly small; the first derivative of distance with respect to time.

#### Fast

Fixed firmly in place; secure
Shutters that are fast against the rain.

#### Speed

The magnitude of a velocity.

#### Fast

Lasting; permanent
Fast rules and regulations.

#### Speed

Swiftness of action
He wrote the first chapter with great speed.

Deep; sound
In a fast sleep.

#### Speed

The act of moving rapidly
Finished the race in a burst of speed.

#### Fast

In a secure manner; tightly
Hold fast.

#### Speed

The state of being in rapid motion; rapidity
The river's speed made a rescue difficult.

#### Fast

To a sound degree; deeply
Fast asleep.

#### Speed

A transmission gear or set of gears in a motor vehicle
What speed is the car in now?.

#### Fast

In a rapid manner; quickly.

#### Speed

A numerical expression of the sensitivity of a photographic film, plate, or paper to light.

#### Fast

In quick succession
New ideas followed fast.

#### Speed

The capacity of a lens to accumulate light at an appropriate aperture.

#### Fast

Ahead of the correct or expected time
A watch that runs fast.

#### Speed

The length of time required or permitted for a camera shutter to open and admit light.

#### Fast

In a dissipated, immoderate way
Living fast.

#### Speed

(Slang) A stimulant drug, especially amphetamine or methamphetamine.

#### Fast

(Archaic) Close by; near.

#### Speed

(Slang) One that suits or appeals to a person's inclinations, skills, or character
Living in a large city is not my speed.

#### Fast

To abstain from food.

#### Speed

(Archaic) Prosperity; luck.

#### Fast

To eat very little or abstain from certain foods, especially as a religious discipline.

#### Speed

To go, move, or proceed quickly
Sped to the rescue.

#### Fast

The act or practice of abstaining from or eating very little food.

#### Speed

To drive at a speed exceeding a legal limit
Was speeding on the freeway.

#### Fast

A period of such abstention or self-denial.

#### Speed

To pass quickly
The days sped by. The months have sped along.

#### Fast

(dated) Firmly or securely fixed in place; stable.
That rope is dangerously loose. Make it fast!

#### Speed

To move, work, or happen at a faster rate; accelerate
His pulse speeded up.

#### Fast

Firm against attack; fortified by nature or art; impregnable; strong.

#### Speed

(Slang) To be under the influence of a stimulant drug.

#### Fast

(of people) Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)

#### Speed

To prove successful; prosper.

#### Fast

Moving with great speed, or capable of doing so; swift, rapid.
I am going to buy a fast car.

#### Speed

To get along in a specified manner; fare.

#### Fast

Having a kinetic energy between 1 million and 20 million electron volts; often used to describe the energy state of free neutrons at the moment of their release by a nuclear fission or nuclear fusion reaction (i.e., before the neutrons have been slowed down by anything).
Plutonium-240 has a much higher fission cross-section for fast neutrons than for thermal neutrons.

#### Speed

To cause to move or proceed quickly; hasten
No wind to speed the boat.

#### Fast

Of a place, characterised by business, hustle and bustle, etc.

#### Speed

To increase the speed or rate of; accelerate. Often used with up
Speed up a car.
Sped up production.

#### Fast

Causing unusual rapidity of play or action.
A fast racket, or tennis court
A fast track
A fast billiard table
A fast dance floor

#### Speed

To further, promote, or expedite (a legal action, for example).

#### Fast

Able to transfer data in a short period of time.

#### Speed

(Archaic) To help to succeed or prosper; aid.

#### Fast

Deep or sound (of sleep); fast asleep (of people).

#### Speed

The state of moving quickly or the capacity for rapid motion.
How does Usain Bolt run at that speed?

#### Fast

(of dyes or colours) Not running or fading when subjected to detrimental conditions such as wetness or intense light; permanent.
All the washing has come out pink. That red tee-shirt was not fast.

#### Speed

The rate of motion or action, specifically the magnitude of the velocity; the rate distance is traversed in a given time.
Speed limits provide information to the drivers about the safe speed to travel in average conditions.

#### Fast

(obsolete) Tenacious; retentive.

#### Speed

(photography) The sensitivity to light of film, plates or sensor.

#### Fast

(dated) Having an extravagant lifestyle or immoral habits.
A fast woman

#### Speed

(photography) The duration of exposure, the time during which a camera shutter is open (shutter speed).

#### Fast

Ahead of the correct time or schedule.
There must be something wrong with the hall clock. It is always fast.

#### Speed

(photography) The largest size of the lens opening at which a lens can be used.

#### Fast

(of photographic film) More sensitive to light than average.

#### Speed

(photography) The ratio of the focal length to the diameter of a photographic objective.

#### Fast

In a firm or secure manner, securely; in such a way as not to be moved; safe, sound .
Hold this rope as fast as you can.

#### Speed

Amphetamine or any amphetamine-based drug (especially methamphetamine) used as a stimulant, especially illegally.

#### Fast

(of sleeping) Deeply or soundly .
He is fast asleep.

#### Speed

(archaic) Luck, success, prosperity.

#### Fast

Immediately following in place or time; close, very near .
The horsemen came fast on our heels.
Fast by the sturdy batsman the ball unheeded sped. / That ain't my style, said Casey. Strike one, the umpire said.

#### Speed

(slang) Personal preference.
We could go to the shore next week, or somewhere else if that's not your speed.

#### Fast

Quickly, with great speed; within a short time .
Do it as fast as you can.

#### Speed

A third-order measure of derivative price sensitivity, expressed as the rate of change of gamma with respect to changes in the underlying asset price.

#### Fast

Ahead of the correct time or schedule.
I think my watch is running fast.

#### Speed

(film) Called by the soundman when the recording equipment has reached running speed and is ready to go.

#### Fast

A train that calls at only some stations it passes between its origin and destination, typically just the principal stations

#### Speed

To succeed; to prosper, be lucky.

#### Fast

The act or practice of fasting, religious abstinence from food

#### Speed

To help someone, to give them fortune; to aid or favour.
God speed, until we meet again.

#### Fast

One of the fasting periods in the liturgical year

#### Speed

(intransitive) To go fast.
The Ferrari was speeding along the road.

#### Fast

(archery) Short for "stand fast", a warning not to pass between the arrow and the target

#### Speed

(intransitive) To exceed the speed limit.
Why do you speed when the road is so icy?

#### Fast

(intransitive) To practice religious abstinence, especially from food.

#### Speed

(transitive) To increase the rate at which something occurs.

#### Fast

To reduce or limit one's nutrition intake for medical or health reasons, to diet.

#### Speed

To be under the influence of stimulant drugs, especially amphetamines.

#### Fast

To abstain from food; to omit to take nourishment in whole or in part; to go hungry.
Fasting he went to sleep, and fasting waked.

#### Speed

(obsolete) To be expedient.

#### Fast

To practice abstinence as a religious exercise or duty; to abstain from food voluntarily for a time, for the mortification of the body or appetites, or as a token of grief, or humiliation and penitence.
Thou didst fast and weep for the child.

#### Speed

(archaic) To hurry to destruction; to put an end to; to ruin.

#### Fast

Abstinence from food; omission to take nourishment.
Surfeit is the father of much fast.

#### Speed

(archaic) To wish success or good fortune to, in any undertaking, especially in setting out upon a journey.

#### Fast

Voluntary abstinence from food, for a space of time, as a spiritual discipline, or as a token of religious humiliation.

#### Speed

To cause to make haste; to dispatch with celerity; to drive at full speed; hence, to hasten; to hurry.

#### Fast

A time of fasting, whether a day, week, or longer time; a period of abstinence from food or certain kinds of food; as, an annual fast.

#### Speed

To hasten to a conclusion; to expedite.

#### Fast

Firmly fixed; closely adhering; made firm; not loose, unstable, or easily moved; immovable; as, to make fast the door.
There is an order that keeps things fast.

#### Speed

Prosperity in an undertaking; favorable issue; success.
O Lord God of my master Abraham, I pray thee, send me good speed this day.

#### Fast

Firm against attack; fortified by nature or art; impregnable; strong.
Outlaws . . . lurking in woods and fast places.

#### Speed

The act or state of moving swiftly; swiftness; velocity; rapidly; rate of motion; dispatch; as, the speed a horse or a vessel.
Speed, to describe whose swiftness number fails.

#### Fast

Firm in adherence; steadfast; not easily separated or alienated; faithful; as, a fast friend.

#### Speed

One who, or that which, causes or promotes speed or success.

#### Fast

Permanent; not liable to fade by exposure to air or by washing; durable; lasting; as, fast colors.

#### Speed

To go; to fare.
To warn him now he is too farre sped.

#### Fast

Tenacious; retentive.
Roses, damask and red, are fast flowers of their smells.

#### Speed

To experience in going; to have any condition, good or ill; to fare.
Ships heretofore in seas like fishes sped; The mightiest still upon the smallest fed.

#### Fast

Not easily disturbed or broken; deep; sound.
All this while in a most fast sleep.

#### Speed

To fare well; to have success; to prosper.
Save London, and send true lawyers their meed!For whoso wants money with them shall not speed!
I told ye then he should prevail, and speedOn his bad errand.

#### Fast

Moving rapidly; quick in mition; rapid; swift; as, a fast horse.

#### Speed

To make haste; to move with celerity.
I have speeded hither with the very extremest inch of possibility.

#### Fast

Given to pleasure seeking; disregardful of restraint; reckless; wild; dissipated; dissolute; as, a fast man; a fast liver.

To be expedient.

#### Fast

In such a condition, as to resilience, etc., as to make possible unusual rapidity of play or action; as, a fast racket, or tennis court; a fast track; a fast billiard table, etc.

#### Speed

To cause to be successful, or to prosper; hence, to aid; to favor.
With rising gales that speed their happy flight.

#### Fast

In a fast, fixed, or firmly established manner; fixedly; firmly; immovably.
We will bind thee fast.

#### Speed

To cause to make haste; to dispatch with celerity; to drive at full speed; hence, to hasten; to hurry.
He sped him thence home to his habitation.

#### Fast

In a fast or rapid manner; quickly; swiftly; extravagantly; wildly; as, to run fast; to live fast.
He, after Eve seduced, unminded slunkInto the wood fast by.
Fast by the throne obsequious Fame resides.

#### Speed

To hasten to a conclusion; to expedite.
Judicial acts . . . are sped in open court at the instance of one or both of the parties.

#### Fast

Abstaining from food

#### Speed

To wish success or god fortune to, in any undertaking, especially in setting out upon a journey.
Welcome the coming, speed the parting guest.

#### Fast

Abstain from certain foods, as for religious or medical reasons;
Catholics sometimes fast during Lent

#### Speed

Distance travelled per unit time

#### Fast

Abstain from eating;
Before the medical exam, you must fast

#### Speed

A rate (usually rapid) at which something happens;
The project advanced with gratifying speed

#### Fast

Acting or moving or capable of acting or moving quickly;
Fast film
On the fast track in school
Set a fast pace
A fast car

#### Speed

Changing location rapidly

#### Fast

(used of timepieces) indicating a time ahead of or later than the correct time;
My watch is fast

#### Speed

The ratio of the focal length to the diameter of a (camera) lens system

#### Fast

At a rapid tempo;
The band played a fast fox trot

#### Speed

A central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression

#### Fast

(of surfaces) conducive to rapid speeds;
Grass courts are faster than clay

#### Speed

Step on it;
He rushed down the hall to receive his guests
The cars raced down the street

#### Fast

Firmly fastened or secured against opening;
Windows and doors were all fast
A locked closet
Left the house properly secured

#### Speed

Move faster;
The car accelerated

Fast colors

#### Speed

Travel at an excessive or illegal velocity;
I got a ticket for speeding

#### Fast

Unrestrained by convention or morality;
Congreve draws a debauched aristocratic society
Riotous living
Fast women

#### Speed

Move very fast;
The runner zipped past us at breakneck speed

#### Fast

Hurried and brief;
Paid a flying visit
Took a flying glance at the book
A quick inspection
A fast visit

#### Speed

Cause to move faster;
He accelerated the car

#### Fast

Securely fixed in place;
The post was still firm after being hit by the car

#### Fast

Unwavering in devotion to friend or vow or cause;
A firm ally
Loyal supporters
The true-hearted soldier...of Tippecanoe
Fast friends

#### Fast

Quickly or rapidly (often used as a combining form);
How fast can he get here?
Ran as fast as he could
Needs medical help fast
Fast-running rivers
Fast-breaking news
Fast-opening (or fast-closing) shutters

#### Fast

Firmly or tightly;
Held fast to the rope
Her foot was stuck fast
Held tight

## Common Curiosities

#### What is speed?

Speed is the rate at which an object moves, measured in units such as mph or kph.

#### How is speed measured?

Speed is measured by dividing the distance an object travels by the time it takes to travel that distance.

#### Can an object be fast but have low speed?

Yes, in relative terms. For example, a person may run fast compared to others but at a low speed in comparison to a car.

#### Is fast always about speed?

Fast generally refers to high speed or quickness but can also describe efficiency or a preference for quickness in non-physical contexts.

#### Are there units for fast?

No, fast is an adjective that describes rapidity but is not measured in units.

#### What does fast mean?

Fast describes something moving or being done with high speed or quickness, without specifying a rate.

#### Why is it important to differentiate between speed and fast?

Differentiating between the two is crucial for clarity in scientific and technical contexts where precision is needed, and for understanding the qualitative vs. quantitative aspects of motion.

#### Can fast be quantified?

Fast is a qualitative term and does not have a specific measurable quantity associated with it, unlike speed.

#### How does context affect the use of speed and fast?

The context determines whether a precise measurement (speed) or a qualitative assessment (fast) is more appropriate to describe motion or efficiency.

#### What role does perception play in determining what is considered fast?

Perception plays a significant role, as what is considered fast can vary greatly depending on the context and comparative standards.

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