Main Difference
The main difference between Speed and Velocity is that the Speed is a magnitude of velocity and Velocity is a rate of change of the position of an object as a function of time, and the direction of that change.
Speed
In everyday use and in kinematics, the speed of an object is the magnitude of its velocity (the rate of change of its position); 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.
Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second, but the most common unit of speed in everyday usage is the kilometre per hour or, in the US and the UK, miles per hour. For air and marine travel the knot is commonly used.
The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c = 299792458 metres per second (approximately 1079000000 km/h or 671000000 mph). Matter cannot quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed.
Velocity
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object’s speed and direction of motion (e.g. 60 km/h to the north). Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.
Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s) or as the SI base unit of (m⋅s−1). 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 has a changing velocity and is said to be undergoing an acceleration.
Speed (noun)
The state of moving quickly or the capacity for rapid motion; rapidity.
“How does Usain Bolt run at that speed?”
Speed (noun)
The rate of motion or action, specifically /the magnitude of the velocity; the rate distance is traversed in a given time.
Speed (noun)
The sensitivity to light of film, plates or sensor.
Speed (noun)
The duration of exposure, the time during which a camera shutter is open.
Speed (noun)
The largest size of the lens opening at which a lens can be used.
Speed (noun)
The ratio of the focal length to the diameter of a photographic objective.
Speed (noun)
Amphetamine or any amphetamine-based drug (especially methamphetamine) used as a stimulant, especially illegally.
Speed (noun)
Luck, success, prosperity.
Speed (noun)
Personal preference.
“We could go to the shore next week, or somewhere else if that’s not your speed.”
Speed (noun)
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.
Speed (verb)
To succeed; to prosper, be lucky.
Speed (verb)
To help someone, to give them fortune; to aid or favour.
“God speed, until we meet again.”
Speed (verb)
To go fast.
“The Ferrari was speeding along the road.”
Speed (verb)
To exceed the speed limit.
“Why do you speed when the road is so icy?”
Speed (verb)
To increase the rate at which something occurs.
Speed (verb)
To be under the influence of stimulant drugs, especially amphetamines.
Speed (verb)
To be expedient.
Speed (verb)
To hurry to destruction; to put an end to; to ruin.
Speed (verb)
To wish success or good fortune to, in any undertaking, especially in setting out upon a journey.
Speed (verb)
To cause to make haste; to dispatch with celerity; to drive at full speed; hence, to hasten; to hurry.
Speed (verb)
To hasten to a conclusion; to expedite.
Velocity (noun)
A vector quantity that denotes the rate of change of position with respect to time, or a speed with the directional component.
Velocity (noun)
Rapidity of motion.
Velocity (noun)
The rate of occurrence.
Velocity (noun)
The number of times that an average unit of currency is spent during a specific period of time.
Speed (noun)
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”
Speed (noun)
rapidity of movement or action
“the accident was due to excessive speed”
Speed (noun)
the rate at which something happens or is done
“the course is delivered on CDROM so students can progress at their own speed”
“they were bemused by the speed of events”
Speed (noun)
each of the possible gear ratios of a bicycle.
Speed (noun)
each of the possible gear ratios of a motor vehicle.
Speed (noun)
the light-gathering power or f-number of a camera lens.
Speed (noun)
the duration of a photographic exposure.
Speed (noun)
the sensitivity of photographic film to light.
Speed (noun)
an amphetamine drug, especially methamphetamine.
Speed (noun)
success; prosperity
“wish me good speed”
Speed (verb)
move quickly
“I got into the car and home we sped”
Speed (verb)
(of a motorist or vehicle) travel at a speed that is greater than the legal limit
“the car that crashed was speeding”
Speed (verb)
move or work more quickly
“you force yourself to speed up because you don’t want to keep others waiting”
Speed (verb)
cause to move or happen more quickly
“they sought to speed up decision-making”
Speed (verb)
make prosperous or successful
“may God speed you”
Speed (verb)
take or be under the influence of an amphetamine drug
“more kids than ever are speeding, tripping, and getting stoned”
Velocity (noun)
the speed of something in a given direction
“the velocities of the emitted particles”
Velocity (noun)
(in general use) speed
“the tank shot backwards at an incredible velocity”
Velocity (noun)
the rate at which money changes hands within an economy.