Instantaneous Speed and Instantaneous Velocity

Instantaneous Speed and Instantaneous Velocity - Definition, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:00 PM IST

The event that occurs with an infinitesimal interval change of time is defined as an instant. Meanwhile, the term average refers to the mean of the total event with respect to total time.In this article, we will discuss what is instantaneous velocity, the instantaneous velocity formula, the S.I unit of instantaneous velocity and instantaneous speed, the difference between instantaneous velocity and average velocity, what is instantaneous speed, the instantaneous speed formula, the difference between instantaneous speed and average speed and difference between instantaneous velocity and instantaneous speed.

This Story also Contains

What is Instantaneous Velocity
Instantaneous Velocity Formula
Difference Between Average Velocity and Instantaneous Velocity
What is Instantaneous Speed
Instantaneous Speed Formula
Difference Between Average Speed and Instantaneous Speed Table
Difference Between Instantaneous Speed and Instantaneous Velocity

Instantaneous Speed and Instantaneous Velocity - Definition, FAQs

What is Instantaneous Velocity

In physics, Instantaneous velocity definition can be given as the rate of change of position for a period of time equal to almost zero (i.e.very small). The SI unit of the instantaneous velocity is given in the terms of meter per second.

The meaning of the velocity of any object is the speed of that object in a particular direction. Instantaneous velocity can be defined as the velocity of any object which is in motion at some particular or specific point time interval. The object which maintains its motion in a uniform velocity, then it possesses an instantaneous velocity which is equal to its standard velocity. The average velocity of any object can be defined as the total displacement by total time period.

Instantaneous Velocity Formula

The instantaneous velocity formula can be represented as the follow:

$$
v_i=\lim _{\Delta t \rightarrow 0} \frac{\Delta s}{\Delta t}
$$

Where,

$\Delta t$ denotes the small change in the time period
$V_i$ denotes the instantaneous velocity
$\Delta s$ refers to the change in the displacement of the object

Related Topics,

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download E-book

SI Unit of the Instantaneous Velocity

The SI unit of the instantaneous velocity is given by $\mathrm{m} / \mathrm{s}$, where $m$ denotes meter and s denotes the second. Instantaneous velocity is a vector quantity. Instantaneous velocity is also defined as the slope of the distance x - time t graph.

$$
\text {Instantaneous Velocity unit }=\frac{\text { meters }(\mathrm{m})}{\text { seconds }(\mathrm{s})}=\mathrm{m} / \mathrm{s}
$$

the graph gives the instantaneous velocity of random object movement

Difference Between Average Velocity and Instantaneous Velocity

Average velocity	Instantaneous velocity
The total displacement by total time period is known as average velocity	The displacement divided by small time period at specific point is known as instantaneous velocity
Average velocity = total displacement/ total time	Instantaneous velocity = displacement for specific point/ time at that instant
The value of average velocity depends on a range of values	The value of the instantaneous velocity depends on an instant value.

What is Instantaneous Speed

In terms of physics, Instantaneous speed definition can be given as the distance travelled per unit time at a given instant.It is the rate at which an object is moving in a given time without considering the direction of its motion. It can be also defined as the instantaneous velocity without considering its direction i.e. it refers to the magnitude of the instantaneous velocity.

The average speed of the object is defined as the total distance divided by the total time taken by the object to move from one point to the other. When the time interval becomes zero, then the distance by the object also becomes zero. But if the limit of the distance ratio to time is not zero, then it is known as instantaneous speed.

Instantaneous Speed Formula

The formula for Instantaneous speed can be given as the follow:

$$
\text { Instantaneous Speed }=\left|\frac{d s}{d t}\right|
$$

Where,

$ds$ denotes the small change in the distance of the object
$dt$ represents the small change in the time period

SI Unit of the Instantaneous Speed

The SI unit of the instantaneous speed is given by $\mathrm{m} / \mathrm{s}$, where m denotes meter in distance and s denotes the second in time. Instantaneous speed is a scalar quantity.

$$
\text {Instantaneous Speed unit }=\frac{\text { meters }(\mathrm{m})}{\text { seconds }(\mathrm{s})}=\mathrm{m} / \mathrm{s}
$$

Difference Between Average Speed and Instantaneous Speed Table

Average speed	Instantaneous speed
The total distance by total time period is known as average speed	The distance divided by small time period at specific point is known as instantaneous speed
Average speed= total distance/ total time	Instantaneous speed= distance for specific point/ time at that instant
The value of average speed depends on a range of values	The value of the instantaneous speed depends on an instant value.

Difference Between Instantaneous Speed and Instantaneous Velocity

The table below shows the difference between instantaneous speed and instantaneous velocity:

Instantaneous speed	Instantaneous velocity
The distance divided by small time period at specific point is known as instantaneous speed	The displacement divided by small time period at specific point is known as instantaneous velocity
Instantaneous speed= distance for specific point/ time at that instant	Instantaneous velocity = displacement for specific point/ time at that instant
The value of the instantaneous speed depends on an instant value.	The value of the instantaneous velocity depends on an instant value.
$ \text { Instantaneous Speed }=\left\|\frac{d s}{d t}\right\| $	$ v_i=\lim _{\Delta t \rightarrow 0} \frac{\Delta s}{\Delta t} $
Instantaneous speed is a scalar quantity	Instantaneous velocity is a vector quantity

Also read:

Frequently Asked Questions (FAQs)

1. Define instantaneous velocity or how do you measure instantaneous velocity?

Instantaneous velocity can be defined as the velocity of any object which is in motion at some particular or specific point time interval.

2. What is the formula for instantaneous velocity?

The instantaneous velocity formula can be represented as the follow:

V_i = lim_Δ_t→0ds/dt

Where, t denotes the small change in the time period

V_i denotes the instantaneous velocity

ds refers to the change in the displacement of the object

t represents the time period

3. What is an average velocity definition or define average velocity?

The average velocity of any object can be defined as the total displacement by total time period.

4. What is the SI unit of the instantaneous velocity?

The SI unit of the instantaneous velocity is given by m/s, where m denotes meter and s denotes the second.

5. Whether Instantaneous velocity is scalar quantity?

No , it is not a scalar quantity. Instantaneous velocity is a vector quantity.

6. Define instantaneous speed or how do you measure instantaneous speed?

The value of the distance divided by a small time period at a specific point is known as instantaneous speed.

7. What is the formula for instantaneous speed?

The formula for Instantaneous speed can be given as the follow:

Instantaneous speed=ds/dt

Where, ds denotes the small change in the distance of the object

dt represents the small change in the time period.

8. What is the SI unit of the instantaneous speed?

The SI unit of the instantaneous speed is given by m/s, where m denotes meter and s denotes the second.

9. Whether Instantaneous speed is vector quantity?

No, It is not a vector quantity, but Instantaneous speed is a scalar quantity.

10. What is the average speed definition or define average speed?

The average speed of the object is defined as the total distance divided by the total time taken by the object to move from one point to the other.

11. What is instantaneous speed?

Instantaneous speed is the speed of an object at a specific moment in time. It's like taking a snapshot of the object's motion at a particular instant. Unlike average speed, which considers the total distance traveled over a period of time, instantaneous speed tells us how fast an object is moving right now.

12. How is instantaneous speed related to the speedometer in a car?

A car's speedometer displays the instantaneous speed of the vehicle. It shows how fast the car is moving at that exact moment, updating continuously as the speed changes.

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

Kinetic energy is directly related to the square of instantaneous speed. The formula for kinetic energy is KE = (1/2)mv², where m is mass and v is instantaneous speed. As speed increases, kinetic energy increases quadratically.

14. How does air resistance affect instantaneous speed?

Air resistance typically opposes motion, causing a decrease in instantaneous speed over time for objects moving through air. The effect becomes more pronounced at higher speeds, leading to a terminal velocity where the force of air resistance equals the force of gravity.

15. Can instantaneous velocity be zero at a non-zero instantaneous speed?

No, this is not possible. If instantaneous velocity is zero, it means the object is momentarily at rest, so its instantaneous speed must also be zero. Velocity can only be zero when speed is zero.

16. How is instantaneous velocity calculated?

Instantaneous velocity is calculated by finding the derivative of the position function with respect to time. Mathematically, it's expressed as v(t) = dx/dt, where v(t) is the instantaneous velocity, x is the position, and t is time.

17. What does a velocity-time graph tell us about instantaneous velocity?

In a velocity-time graph, the y-coordinate of any point represents the instantaneous velocity at that time. The slope of the tangent line at any point on this graph represents the instantaneous acceleration.

18. How does instantaneous velocity relate to displacement?

Instantaneous velocity at any point is tangent to the displacement curve at that point. It represents the rate of change of displacement with respect to time at a particular instant.

19. How does the concept of limits relate to instantaneous velocity?

Instantaneous velocity is defined using the concept of limits. It's the limit of average velocity as the time interval approaches zero. This allows us to find the velocity at a single point in time, which would otherwise be impossible to measure directly.

20. What's the significance of the sign of instantaneous velocity?

The sign of instantaneous velocity indicates the direction of motion relative to the chosen coordinate system. A positive velocity typically means the object is moving in the positive direction of the coordinate axis, while a negative velocity means it's moving in the negative direction.

21. Can instantaneous speed ever exceed the average speed over a time interval?

Yes, instantaneous speed can exceed the average speed. For example, if a car accelerates from rest, its instantaneous speed at the end of the time interval will be higher than its average speed over that interval.

22. Can instantaneous velocity be infinite?

In classical physics, instantaneous velocity cannot be infinite as this would violate the laws of physics, particularly the speed of light as the universal speed limit. In quantum mechanics, there are some situations where apparent "infinite" velocities can occur, but these are still subject to debate and interpretation.

23. How does relativistic physics affect our understanding of instantaneous velocity?

In special relativity, the concept of instantaneous velocity becomes more complex. As objects approach the speed of light, classical notions of velocity break down, and we must consider effects like time dilation and length contraction.

24. What's the relationship between instantaneous velocity and instantaneous acceleration?

Instantaneous acceleration is the rate of change of instantaneous velocity with respect to time. Mathematically, it's the derivative of the velocity function or the second derivative of the position function with respect to time.

25. What's the difference between instantaneous speed and instantaneous rate of change?

Instantaneous speed is a specific type of instantaneous rate of change, particularly the rate of change of distance with respect to time. Instantaneous rate of change is a more general concept that can apply to any quantity changing over time.

26. What's the difference between average velocity and instantaneous velocity?

Average velocity is calculated over a period of time, while instantaneous velocity is the velocity at a specific moment. Average velocity gives an overall picture of motion, while instantaneous velocity provides a precise snapshot at a particular instant.

27. Can an object have different instantaneous velocities at the same position?

Yes, an object can have different instantaneous velocities at the same position at different times. For example, a ball thrown straight up will have different velocities when it passes a certain height on its way up versus on its way down.

28. How does instantaneous velocity relate to momentum?

Momentum is the product of mass and velocity. Therefore, instantaneous momentum is directly proportional to instantaneous velocity. If we know an object's mass and instantaneous velocity, we can calculate its instantaneous momentum.

29. How does instantaneous velocity change during projectile motion?

In projectile motion, the horizontal component of instantaneous velocity remains constant (ignoring air resistance), while the vertical component changes continuously due to gravity. This results in a parabolic path.

30. How does instantaneous velocity relate to acceleration?

Instantaneous acceleration is the rate of change of instantaneous velocity with respect to time. Mathematically, a(t) = dv/dt, where a(t) is instantaneous acceleration and v is instantaneous velocity.

31. How does instantaneous velocity differ from instantaneous speed?

Instantaneous velocity includes both speed and direction, while instantaneous speed is just the magnitude of velocity. Velocity is a vector quantity, meaning it has both magnitude and direction, whereas speed is a scalar quantity, having only magnitude.

32. Can instantaneous speed be negative?

No, instantaneous speed cannot be negative. Speed is always a positive scalar quantity, representing the magnitude of how fast an object is moving, regardless of direction. Velocity, on the other hand, can be positive or negative depending on the direction of motion.

33. Can an object have zero instantaneous velocity but non-zero instantaneous speed?

No, this is not possible. If an object has zero instantaneous velocity, it means it's not moving at that exact moment, so its instantaneous speed must also be zero. Remember, speed is the magnitude of velocity.

34. Can instantaneous velocity be constant while instantaneous speed varies?

No, if instantaneous velocity is constant, instantaneous speed must also be constant. This is because speed is the magnitude of velocity. If velocity (including direction) doesn't change, speed can't change either.

35. Can an object have constant speed but varying instantaneous velocity?

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

36. How does instantaneous velocity relate to relative motion?

Instantaneous velocity is always measured relative to a frame of reference. The same object can have different instantaneous velocities when measured from different reference frames moving relative to each other.

37. What's the relationship between instantaneous velocity and position?

Instantaneous velocity is the rate of change of position with respect to time. Mathematically, it's the first derivative of the position function. If you know the instantaneous velocity function, you can integrate it to find the position function.

38. How does the uncertainty principle affect our ability to measure instantaneous velocity?

The Heisenberg uncertainty principle states that we cannot simultaneously know both the exact position and momentum (which is related to velocity) of a particle. This introduces a fundamental limit to the precision with which we can measure instantaneous velocity at the quantum level.

39. Can an object have instantaneous velocity in more than one dimension?

Yes, in two or three-dimensional motion, instantaneous velocity is a vector quantity with components in each dimension. For example, in 3D space, velocity would have x, y, and z components, each representing the rate of change of position in that direction.

40. How does instantaneous velocity relate to wave motion?

In wave motion, particles in the medium have instantaneous velocities that oscillate as the wave passes. The wave itself also has a velocity (phase velocity) which is different from the instantaneous velocity of the particles.

41. What's the difference between instantaneous velocity and instantaneous angular velocity?

Instantaneous velocity describes linear motion and is measured in units of distance per time (e.g., m/s). Instantaneous angular velocity describes rotational motion and is measured in units of angle per time (e.g., radians/s).

42. How does instantaneous velocity relate to the concept of frames of reference?

Instantaneous velocity is always measured relative to a specific frame of reference. The same object can have different instantaneous velocities when observed from different frames of reference. This is a key concept in understanding relative motion and Einstein's theory of relativity.

43. How does the concept of instantaneous velocity apply to fluid dynamics?

In fluid dynamics, we often deal with flow velocity, which is the instantaneous velocity of fluid particles at a given point in space and time. This concept is crucial for understanding phenomena like laminar and turbulent flow, pressure differences, and fluid behavior in various systems.

44. Can an object have constant instantaneous speed but varying instantaneous velocity?

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

45. How does instantaneous velocity relate to the concept of work in physics?

Work is defined as the dot product of force and displacement. Instantaneous velocity plays a role in calculating instantaneous power, which is the rate at which work is done. Instantaneous power is the dot product of force and instantaneous velocity.

46. What's the significance of instantaneous velocity in understanding motion graphs?

In position-time graphs, the instantaneous velocity at any point is represented by the slope of the tangent line at that point. In velocity-time graphs, the instantaneous velocity is directly given by the y-coordinate of any point on the graph.

47. How does the concept of instantaneous velocity apply to quantum particles?

In quantum mechanics, the concept of instantaneous velocity becomes more complex. Due to the wave-particle duality and the uncertainty principle, we can't always assign a definite position and velocity to a particle simultaneously. Instead, we often work with probability distributions and expectation values.

48. Can instantaneous velocity be measured directly?

Strictly speaking, instantaneous velocity cannot be measured directly as it represents the velocity at a single instant of time. In practice, we approximate it by measuring average velocity over very small time intervals or by using instruments that can take measurements at very high frequencies.

49. How does instantaneous velocity relate to the concept of impulse?

Impulse is defined as the change in momentum over time. Since momentum is the product of mass and velocity, instantaneous velocity plays a crucial role in determining the instantaneous rate of change of momentum, which is related to the instantaneous force acting on an object.

50. What's the relationship between instantaneous velocity and the wave function in quantum mechanics?

In quantum mechanics, the wave function describes the state of a particle. The expectation value of velocity can be calculated using the wave function and the velocity operator. This gives us a quantum analog to classical instantaneous velocity, though it behaves differently due to the probabilistic nature of quantum mechanics.

51. How does instantaneous velocity relate to the concept of phase space in classical mechanics?

In phase space, a point represents both the position and momentum (which is related to velocity) of a system at an instant. The instantaneous velocity contributes to defining the system's state in this space, allowing us to describe and analyze complex dynamical systems.

52. Can an object have different instantaneous speeds in different reference frames?

Yes, the instantaneous speed of an object can be different when measured from different reference frames that are moving relative to each other. This is a consequence of the relativity of motion and is described by the velocity addition formula in special relativity.

53. How does instantaneous velocity relate to the concept of proper time in relativity?

In special relativity, proper time is the time measured by a clock moving with an object. The rate at which proper time passes depends on the object's instantaneous velocity relative to other reference frames, leading to effects like time dilation.

54. What's the significance of instantaneous velocity in understanding conservation of energy?

Instantaneous velocity is crucial in calculating kinetic energy, which is a key component in the principle of conservation of energy. Changes in instantaneous velocity result in changes in kinetic energy, which must be balanced by changes in other forms of energy in a closed system.

55. How does the concept of instantaneous velocity apply to rotational motion?

In rotational motion, we use angular velocity instead of linear velocity. Instantaneous angular velocity describes how fast an object is rotating at a particular instant, measured in radians per second. It's related to linear velocity by the equation v = rω, where r is the radius of rotation and ω is the angular velocity.

56. Can instantaneous velocity be complex-valued?

In classical physics, instantaneous velocity is always real-valued. However, in some areas of quantum mechanics and mathematical physics, complex-valued velocities can arise in certain formulations, though their physical interpretation can be challenging.

57. How does instantaneous velocity relate to the concept of phase velocity in wave mechanics?

Phase velocity is the rate at which the phase of a wave propagates in space. It's different from the instantaneous velocity of particles in the medium. In some cases, phase velocity can exceed the speed of light, while the instantaneous velocity of energy or information transfer (group velocity) cannot.

58. What's the relationship between instantaneous velocity and the Doppler effect?

The Doppler effect occurs when there's relative motion between a wave source and an observer. The instantaneous velocity of the source or observer affects the observed frequency of the wave. This principle is used in various applications, from weather radar to measuring the speed of distant galaxies.

59. How does the concept of instantaneous velocity apply to fields in physics?

In field theories, we often deal with field velocities, which describe how quickly field values are changing at a point in space and time. For example, in electromagnetism, the rate of change of electric and magnetic fields is crucial for understanding wave propagation and energy transfer.

60. Can instantaneous velocity be defined for non-material objects, like waves or information?

Yes, we can define instantaneous velocity for non-material entities. For waves, we have phase velocity and group velocity. For information, we consider the speed at which information can propagate, which is limited by the speed of light according to special relativity. These concepts extend our understanding of velocity beyond just material objects.