Measurement of Speed - Definition, Formula, Unit, Types, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:32 PM IST

Imagine a car traveling on a road. The distance it covers in a certain amount of time tells us how fast it is moving—this is its speed. Speed is the rate at which an object moves or changes its position over time. Speed is an important phenomenon in Physics, Let's explore the concept of speed along with its calculation in detail.

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What is Speed?
How to Calculate Speed?
Types of Speed

Measurement of Speed - Definition, Formula, Unit, Types, FAQs

What is Speed?

"The rate at which anybody moves or operates with respect to time is called the speed of the body."

In physics, the measurement of speed refers to the rate of change of position of a body with respect to time. The measurement of speed may vary according to the condition it is applied to.

The unit of speed is the meter per second ( $\mathrm{m} / \mathrm{s}$ ).

How to Calculate Speed?

Mathematically speed is represented as:

Speed $=\frac{\text { Distance }}{\text { Time }}$
Where:

Distance is measured in meters (m) in the SI system.
Time is measured in seconds (s) in the SI system.

Dimensional Formula for Speed

The dimensional formula for speed is:

$[$ Speed $]=[L][T]^{-1}$
Where:

[L]: Length (meters, m)
$[T]^{-\mathbf{1}}:$ Time inverse (seconds, $s^{-\mathbf{1}}$ )

This confirms that speed is measured in $\mathbf{m} / \mathbf{s}$ in the SI system.

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Types of Speed

Average Speed
Instantaneous Speed
Uniform Speed
Non-Uniform Speed
Relative Speed

]Related Topics

Average Speed

Average speed can be defined as the total distance covered divided by the total time taken.

Average Speed $=\frac{\text { Total Distance }}{\text { Total Time }}$

Example:

A car covers 100 km in 2 hours, resulting in an average speed of $\frac{\mathbf{1 0 0}}{2}=50 \mathrm{~km} / \mathrm{h}$.

Instantaneous Speed

It is the measure of speed of a body at any instant of time, or measuring the rate of change of position with respect to an infinitesimally small time period.

Instantaneous Speed $=\left|\frac{d s}{d t}\right|$
Where:
$d s$ : Infinitesimal change in distance
$d t$ : Infinitesimal change in time

Uniform Speed

Uniform speed indicates a case of motion of an object where the rate of change of position to time is constant throughout the motion, in which the object covers an equal distance in equal intervals of time.

When considering the graph it will be a straight line with a constant slope, that is if we take the slope of the graph between any two points on the graph, it will remain the same always.(we have seen what the slope in a distance vs time graph indicates, it indicates the speed)

Uniform Speed

Non-Uniform Speed

An object is said to be in non-uniform motion when there is an acceleration on the body that is the speed does not always remain the same throughout the motion, it may increase or decrease accordingly.

The rate of increase or decrease of velocity with respect to time is called acceleration, we have talked about uniform and non-uniform speed similarly there can be uniform or non-uniform acceleration also. Acceleration is a vector quantity so it cannot be mentioned in terms of speed but the magnitude of acceleration can be the rate of change of speed.

non-uniform speed

Relative Speed

The speed of one object with respect to another object is called as relative speed.

Relative Speed $=\left|v_1-v_2\right|$

Example:

If two cars are moving in opposite directions at $60 \mathrm{~km} / \mathrm{h}$ and $40 \mathrm{~km} / \mathrm{h}$, their relative speed is $60+40=100 \mathrm{~km} / \mathrm{h}$.

Frequently Asked Questions (FAQs)

1. What is speed or what is speed in physics or define speed in physics or speed definition physics or what is definition of speed and its speed formula ? or what is the formula for speed ?

Speedo meaning is rate of change of position to time and speed is a scalar quantity, it contains only magnitude and does not contain direction. Formula for speed is Speed = distance/time

2. What is variable speed? or define variable speed.

If a body undergoes any kind of acceleration, then the body is said to have variable speed, that is the speed is not constant at equal intervals of time.

3. Provide the example of speed.

The example of speed or application of speed is

Speed of the vehicle
Speed of rotation of the fan
Speed of revolution of planets around sun

4. Optimum speed meaning in case of a rotor of a water pump.

It means the required number of rotations per unit time such that enough water is pumped into the surface, more rotation implies more water gets pumped.

5. What are the characteristics of speed?

Speed is the measure of motion and it can directly imply the amount of kinetic energy possessed by the body. If a body is said to have more speed than that of the other then it implies it can cover a much higher distance in less time.

6. Can an object have a constant speed but not a constant velocity?

Yes, this is possible. An object moving in a circular path at a constant speed has a changing velocity because its direction is constantly changing, even though its speed remains the same.

7. How does acceleration relate to speed?

Acceleration is the rate of change of velocity over time. When an object accelerates, its speed is changing - either increasing (positive acceleration) or decreasing (negative acceleration or deceleration).

8. What is terminal velocity?

Terminal velocity is the maximum speed that an object can achieve when falling through a fluid (like air or water) under the force of gravity. It occurs when the downward force of gravity equals the upward force of air resistance.

9. How does air resistance affect the speed of a falling object?

Air resistance opposes the motion of a falling object, causing it to accelerate more slowly than it would in a vacuum. Eventually, the air resistance becomes equal to the gravitational force, and the object reaches its terminal velocity.

10. What is the speed of light and why is it significant?

The speed of light in a vacuum is approximately 299,792,458 meters per second. It's significant because it's the fastest speed at which any information or matter can travel in the universe, according to Einstein's theory of relativity.

11. What is speed in physics?

Speed is a measure of how quickly an object moves from one point to another. It is calculated by dividing the distance traveled by the time taken. Speed tells us how fast something is moving, but it doesn't tell us the direction of motion.

12. How is speed different from velocity?

Speed is a scalar quantity that only measures how fast an object is moving, while velocity is a vector quantity that includes both speed and direction. For example, a car traveling at 60 km/h is its speed, but 60 km/h north is its velocity.

13. What are the SI units for speed?

The SI unit for speed is meters per second (m/s). However, in everyday life, we often use kilometers per hour (km/h) or miles per hour (mph).

14. Can speed ever be negative?

No, speed cannot be negative. Speed is the magnitude of velocity and is always positive or zero. A negative value would not make sense for speed, as it only measures how fast something is moving, not its direction.

15. What's the difference between instantaneous speed and average speed?

Instantaneous speed is the speed of an object at a specific moment in time, while average speed is calculated over a period of time. Instantaneous speed can vary moment to moment, but average speed gives an overall picture of the motion.

16. What is the formula for calculating average speed?

The formula for average speed is: Average Speed = Total Distance / Total Time. This gives us the overall speed for an entire journey, even if the speed varied during the trip.

17. What's the relationship between kinetic energy and speed?

Kinetic energy is directly related to speed. The formula for kinetic energy is KE = (1/2)mv², where m is mass and v is velocity. This means that doubling an object's speed will quadruple its kinetic energy.

18. How do you convert km/h to m/s?

To convert km/h to m/s, multiply the speed in km/h by 1000 (to convert km to m) and divide by 3600 (to convert hours to seconds). Alternatively, you can multiply the speed in km/h by 5/18. For example, 36 km/h = 36 × (5/18) = 10 m/s.

19. What is uniform motion?

Uniform motion is when an object travels at a constant speed in a straight line. In uniform motion, the object covers equal distances in equal intervals of time, and its speed doesn't change.

20. What's the difference between speed and pace?

Speed measures how fast an object is moving (distance per unit time), while pace measures how long it takes to cover a specific distance (time per unit distance). For example, a speed of 10 km/h is equivalent to a pace of 6 minutes per kilometer.

21. How does mass affect the speed of an object?

Mass itself doesn't directly affect speed. However, it does affect acceleration. Given the same force, an object with less mass will accelerate more quickly than an object with more mass, potentially reaching a higher speed in a shorter time.

22. What is the concept of group velocity in waves?

Group velocity is the speed at which the overall shape of a wave's amplitudes travels. It's often different from the phase velocity, which is the speed of individual wave crests. Group velocity is important in understanding how information or energy is transmitted by waves.

23. What is the concept of frame-dragging in general relativity?

Frame-dragging is an effect in Einstein's theory of general relativity where the rotation of a massive object "drags" the fabric of spacetime around with it. This can affect the speed and path of objects moving near the rotating mass.

24. What is the concept of group delay in signal processing?

Group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a system. It's the negative derivative of the phase response with respect to frequency and is important in understanding signal transmission speeds.

25. What is the concept of characteristic velocity in rocketry?

Characteristic velocity in rocketry is a measure of the efficiency of the rocket's engine, independent of other factors like atmospheric pressure. It's calculated as the product of the exhaust velocity and a factor related to the chamber pressure and nozzle expansion.

26. What is the relationship between speed and kinematic viscosity in fluid dynamics?

Kinematic viscosity is the ratio of dynamic viscosity to density and has units of area per time, often expressed as stokes. It affects the speed at which a fluid flows under certain conditions, with higher kinematic viscosity generally resulting in slower flow speeds for a given pressure gradient.

27. How do we measure the speed of very fast-moving objects?

For very fast-moving objects, we often use sophisticated equipment like radar guns, laser speed detectors, or high-speed cameras. These devices can measure speed by detecting changes in waves (like light or radio waves) reflected off the moving object.

28. What is relative speed?

Relative speed is the speed of an object as observed from a particular frame of reference. For example, if you're walking forward in a train that's moving, your speed relative to the train is different from your speed relative to the ground outside.

29. How do we calculate the average speed when an object travels at different speeds?

To calculate average speed when an object travels at different speeds, we use the total distance traveled divided by the total time taken. It's not the average of the different speeds.

30. What is the difference between speed and rapidity?

In everyday language, these terms are often used interchangeably. However, in physics, speed is a scalar quantity (magnitude only), while rapidity is a more complex concept used in relativity theory to describe motion at very high speeds.

31. Can an object's speed ever exceed its velocity?

No, an object's speed cannot exceed its velocity. Speed is the magnitude of velocity, so it's always less than or equal to the velocity. They're equal only when the motion is in a straight line.

32. How does gravity affect the speed of a falling object?

In the absence of air resistance, gravity causes a falling object to accelerate at about 9.8 m/s² near Earth's surface. This means its speed increases by 9.8 m/s every second it falls.

33. What is the concept of escape velocity?

Escape velocity is the minimum speed an object needs to escape a planet's gravitational field without further propulsion. For Earth, this speed is about 11.2 km/s at the surface.

34. How do speedometers in vehicles work?

Most vehicle speedometers work by measuring the rotational speed of the drive shaft or wheel. This is typically done using a magnetic sensor or a mechanical connection, which is then converted into a speed reading.

35. What is the relationship between frequency, wavelength, and speed for waves?

For all waves, the relationship between frequency (f), wavelength (λ), and speed (v) is given by the equation: v = f × λ. This means that for a given speed, as frequency increases, wavelength decreases, and vice versa.

36. How do we measure the speed of sound?

The speed of sound can be measured by creating a loud noise and measuring the time it takes for the sound to travel a known distance. More precise methods involve using specialized equipment like interferometers or pulse-echo techniques.

37. How does the medium affect the speed of a wave?

The properties of the medium through which a wave travels greatly affect its speed. For example, sound waves travel faster in solids than in liquids, and faster in liquids than in gases, due to the differences in the elastic properties and density of these media.

38. What is the concept of drift velocity in electric current?

Drift velocity is the average velocity of charge carriers (like electrons) in a conductor when an electric field is applied. It's typically very slow (millimeters per second) despite the rapid propagation of the electric field effect.

39. How do we measure the speed of subatomic particles?

The speed of subatomic particles is often measured indirectly using various detection methods. These include cloud chambers, bubble chambers, and more modern particle detectors that can track the paths and energies of particles.

40. What is the relationship between angular speed and linear speed?

For an object moving in a circular path, the linear speed (v) is related to the angular speed (ω) by the equation: v = ω × r, where r is the radius of the circular path. This shows that points farther from the center of rotation have a higher linear speed.

41. How does the concept of speed apply to chemical reactions?

In chemistry, the speed of a reaction refers to the rate at which reactants are converted into products. It's often expressed as the change in concentration of a reactant or product per unit time.

42. What is the concept of phase velocity?

Phase velocity is the speed at which the phase of a wave propagates in space. It's given by the equation: v_p = ω / k, where ω is the angular frequency and k is the wave number. In some cases, phase velocity can exceed the speed of light, but this doesn't violate relativity as it doesn't carry information.

43. How does temperature affect the speed of molecules in a gas?

As temperature increases, the average kinetic energy of gas molecules increases, causing them to move faster. This relationship is described by the kinetic theory of gases, where the average speed of gas molecules is proportional to the square root of the temperature.

44. How do we measure the speed of tectonic plate movement?

The speed of tectonic plate movement is typically measured using GPS technology, which can detect minute changes in position over time. Other methods include studying magnetic patterns in rocks and measuring the spread of seafloor at mid-ocean ridges.

45. What is the relationship between speed and time dilation in special relativity?

According to special relativity, as an object's speed approaches the speed of light, time passes more slowly for that object relative to a stationary observer. This effect, known as time dilation, becomes significant at very high speeds.

46. How does the speed of neutrinos compare to the speed of light?

Neutrinos are subatomic particles that travel at speeds very close to, but not exceeding, the speed of light. Recent experiments have measured neutrino speeds to be consistent with the speed of light within the margin of error of the experiments.

47. What is the concept of superluminal motion in astronomy?

Superluminal motion is an apparent faster-than-light movement seen in some astronomical radio sources. It's an optical illusion caused by the source moving at a high velocity at a small angle to the line of sight, not actual faster-than-light travel.

48. How do we measure the orbital speed of planets?

The orbital speed of planets can be calculated using Kepler's laws of planetary motion. We can also measure it directly using the Doppler effect, observing how the light from the planet (or its star) is shifted as it moves towards or away from Earth.

49. How does the speed of a tsunami compare to regular ocean waves?

Tsunamis travel much faster than regular ocean waves. In the deep ocean, tsunamis can reach speeds over 800 km/h, while typical ocean waves move at about 90 km/h. This is because tsunamis involve the movement of water all the way to the ocean floor, not just the surface.

50. What is the concept of proper velocity in relativity?

Proper velocity is the rate of change of proper distance (distance measured in the object's rest frame) with respect to proper time (time measured in the object's rest frame). Unlike coordinate velocity, proper velocity can exceed the speed of light, though this doesn't violate relativity.

51. How do we measure the speed of continental drift?

The speed of continental drift is measured using various techniques, including GPS measurements, studying magnetic patterns in rocks, and analyzing the distribution of fossils. Modern measurements show that continents move at speeds of a few centimeters per year.

52. What is the relationship between speed and momentum?

Momentum is the product of an object's mass and velocity. As speed (the magnitude of velocity) increases, momentum increases proportionally if mass remains constant. This relationship is expressed in the formula: p = mv, where p is momentum, m is mass, and v is velocity.

53. How does the speed of light in a medium relate to its refractive index?

The speed of light in a medium is inversely proportional to the medium's refractive index. The relationship is given by v = c/n, where v is the speed of light in the medium, c is the speed of light in vacuum, and n is the refractive index of the medium.

54. How do we measure the speed of nerve impulses in the human body?

The speed of nerve impulses is typically measured by stimulating a nerve at one point and recording the time it takes for the signal to reach another point. This can be done using electrodes placed on the skin or inserted near the nerve.

55. How does the speed of a shock wave compare to the speed of sound?

A shock wave travels faster than the speed of sound in the medium. The ratio of the shock wave speed to the speed of sound is called the Mach number. When this number is greater than 1, it indicates supersonic flow and the formation of a shock wave.