Motion in Physics - Definition, FAQs

Q: What is the distinction between uniform and non-uniform motion?

Uniform Motion Non-uniform Motion An object covers equal distance in equal interval of time then object is said to have uniform motion. When an object travels an unequal distance in an equal amount of time, it is said to be moving in a non-uniform manner/motion . Steady speed or velocity Variable speed or velocity Graph plotting between distance along with time is always a straight line. Graph plotting between distance along with time is Not a straight line. Acceleration is Zero. Acceleration is non-zero.

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

What is motion in Physics?

Motion definition physics: Motion in physics, movement is a phenomenon in which an object over time changes position. In terms of movement, distance, speed, acceleration and time, motion is described quantitatively.

Motion in Physics - Definition, FAQs

Three laws of motion

The movement of huge bodies is described in physics by two related sets of mechanical rules. Classical mechanics describe motion in the Universe for all huge as well as recognisable items

The three rules of classical mechanics were formulated by Newton as well as Euler historically:

The three equations of motion are as follows:

1. $v=u+a t$
2. $S=u t+\frac{1}{2} a t^2$
3. $V^2=u^2+2 a s$

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Newton's 1st law of motion or law of inertia.

"Everything continues to be in its state of rest or uniform motion along a straight line unless driven to act otherwise by some other body," Newton's first law states. The property of a body that resists changes in its state of rest or uniform motion is known as inertia. If the total external force is zero, an object in uniform motion will remain in uniform motion, and an object at rest will remain at rest.

Newton's second law of motion

The vector sum of the forces F on an object in an inertial reference frame equals the object's mass m multiplied by its acceleration.

F=ma

It is a vector quantity

SI Unit Newton (N)

Newton's third law of motion

When one body puts a force on another, the second body simultaneously exerts a force on the first body that is equal in size and opposite in direction.

Action = -reaction

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Translational motion

The driving force F is balanced in translational motion by a resisting force F_r generated by the driven machine and an inertia force Ma generated by the change in speed, or

F-F_r=Ma=Mdv/dt

Where M is the mass given in kilogrammes the velocity v in metres per second, the acceleration an in metres per second², and the force F in Newton (N)

Oscillatory motion

Periodic or oscillatory motion is defined as a motion that repeats itself. Due to a restoring force or torque, an object in such motion oscillates around an equilibrium position. No matter which direction the system is moved, such force or torque tends to restore (return) the system to its equilibrium position.

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Rotational motion

In rotational motion, the driving torque T_m (often generated by an electric motor) is balanced by a resisting torque T_L (typically generated by the load and referred to as the motor shaft) and inertia or dynamic torque Jdω/dt.

$\mathrm{T}_{\mathrm{M}}-\mathrm{T}_{\mathrm{L}}=\mathrm{Jd} \omega / \mathrm{dt}$.

Where $J$ is the moment of inertia given in $\mathrm{kg}^* \mathrm{~m}^2$ It is also known as a flywheel.

Torque or moment, where $T$ is the torque in $N^* m$. The signs to be associated

With $T_M$ and $T_L$ in Eq. (2) are determined by the driving motor's operating regime and the nature of the load torque.

Relativistic mechanics

Modern kinematics evolved from the study of electromagnetic and refers to all velocities v in terms of their ratio to the speed of light c. Velocity is thus understood as rapidity, the hyperbolic angle for which the hyperbolic tangent function tan h = v/c. Acceleration, or a change in velocity, affects rapidity according to Lorentz transformations. This branch of mechanics is known as special relativity. W. K. Clifford and Albert Einstein both attempted to incorporate gravity into relativistic mechanics. The development employed differential geometry to describe a curved cosmos with gravity; the research is known as general relativity.

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Frequently Asked Questions (FAQs)

1. What is the formula for motion?

The fundamental equation of motion in classical mechanics is Newton's second law, which states force F acting on body is equal to mass of an object multiplied by acceleration (a), F = ma.

2. What is an example of uniform motion?

When an object moves in a straight line at constant speed, it is said to be moving with uniform motion. When a car travels at a steady speed, resistive forces such as air resistance as well as frictional forces in automobile's moving parts balance the engine's driving power.

3. What is the distinction between uniform and non-uniform motion?

Uniform Motion	Non-uniform Motion
An object covers equal distance in equal interval of time then object is said to have uniform motion.	When an object travels an unequal distance in an equal amount of time, it is said to be moving in a non-uniform manner/motion .
Steady speed or velocity	Variable speed or velocity
Graph plotting between distance along with time is always a straight line.	Graph plotting between distance along with time is Not a straight line.
Acceleration is Zero.	Acceleration is non-zero.

4. How is motion different from rest?

Motion involves a change in position over time, while rest means an object maintains its position relative to a reference point. However, rest is relative - an object at rest in one frame of reference may be in motion in another.

5. Can an object be in motion and at rest simultaneously?

Yes, an object can be in motion relative to one frame of reference while at rest relative to another. For example, a passenger sitting in a moving car is at rest relative to the car but in motion relative to the road.

6. What is a frame of reference in motion?

A frame of reference is a coordinate system or set of axes relative to which an object's position and motion are described. It's crucial because motion is always measured relative to a chosen reference point or frame.

7. What is displacement in motion?

Displacement is the shortest distance between an object's initial and final positions, along with the direction of that change. It's a vector quantity, meaning it has both magnitude and direction.

8. What is velocity in physics?

Velocity is the rate of change of displacement with respect to time. It's a vector quantity that describes both the speed and direction of an object's motion.

9. What is motion in physics?

Motion in physics is the change in position of an object over time relative to a reference point. It involves the continuous change of an object's location in space.

10. How is displacement different from distance traveled?

Displacement is the straight-line distance and direction from start to end points, while distance traveled is the total length of the path taken. Displacement can be less than or equal to distance traveled, but never greater.

11. How does speed differ from velocity?

Speed is a scalar quantity that measures how fast an object is moving, regardless of direction. Velocity is a vector quantity that includes both speed and direction of motion.

12. What is acceleration in motion?

Acceleration is the rate of change of velocity with respect to time. It describes how quickly an object's speed or direction is changing and is also a vector quantity.

13. What is the difference between average velocity and instantaneous velocity?

Average velocity is the total displacement divided by the total time taken, while instantaneous velocity is the velocity of an object at a specific instant or point in time.

14. What is the significance of slope in position-time graphs?

The slope of a position-time graph represents the velocity of the object. A steeper slope indicates higher velocity, while a horizontal line shows zero velocity (the object is at rest).

15. How can you determine if motion is accelerating from a velocity-time graph?

Acceleration is represented by the slope of a velocity-time graph. A straight line with non-zero slope indicates constant acceleration, while a curved line shows changing acceleration.

16. What is negative acceleration?

Negative acceleration, also known as deceleration, occurs when an object's speed decreases over time or when it accelerates in the direction opposite to its motion.

17. Can an object have constant acceleration but changing speed?

Yes, this occurs in projectile motion. An object thrown upward has constant downward acceleration due to gravity, but its speed decreases as it rises and increases as it falls.

18. How does air resistance affect the motion of falling objects?

Air resistance opposes the motion of falling objects, causing them to reach a terminal velocity where the upward force of air resistance equals the downward force of gravity, resulting in zero acceleration.

19. How does mass affect an object's acceleration in free fall?

In the absence of air resistance, all objects, regardless of mass, accelerate at the same rate in free fall. This is because the gravitational force increases proportionally with mass.

20. How do you calculate average speed?

Average speed is calculated by dividing the total distance traveled by the total time taken. It's a scalar quantity and doesn't consider direction.

21. Can an object have zero velocity but non-zero acceleration?

Yes, this occurs at the highest point of a vertical throw or at the moment an object changes direction. The velocity is momentarily zero, but there's still acceleration (e.g., due to gravity).

22. What is the significance of area under a velocity-time graph?

The area under a velocity-time graph represents the displacement of the object over that time interval. This is because displacement is the product of velocity and time.

23. How does changing the frame of reference affect observed motion?

Changing the frame of reference can alter the perceived motion of an object. For example, a ball dropped in a moving train appears to fall straight down to a passenger on the train, but follows a parabolic path when viewed from outside.

24. What is the importance of significant figures in motion calculations?

Significant figures indicate the precision of a measurement or calculation. In motion problems, maintaining the correct number of significant figures ensures that the precision of the result matches the precision of the given data.

25. How does gravity affect horizontal motion?

Gravity doesn't directly affect horizontal motion. However, it causes vertical acceleration in projectile motion, resulting in a parabolic path when combined with horizontal motion.

26. What is the difference between distance and magnitude of displacement?

Distance is always positive and represents the total path length, while the magnitude of displacement is the straight-line distance between start and end points, which can be less than or equal to the distance traveled.

27. What is the role of calculus in understanding motion?

Calculus is fundamental in describing motion. Differentiation helps find instantaneous velocity and acceleration from position functions, while integration allows calculating displacement from velocity or velocity from acceleration.

28. What is the physical meaning of the area under an acceleration-time graph?

The area under an acceleration-time graph represents the change in velocity over that time interval. This is because velocity is the integral of acceleration with respect to time.

29. How do we describe motion in two or three dimensions?

Motion in multiple dimensions is described by breaking it down into component motions along each axis. For example, projectile motion combines constant velocity in the horizontal direction with accelerated motion in the vertical direction.

30. What is the difference between average acceleration and instantaneous acceleration?

Average acceleration is the change in velocity over a time interval, while instantaneous acceleration is the acceleration at a specific moment in time, calculated as the limit of average acceleration as the time interval approaches zero.

31. How does the concept of relative velocity apply in everyday situations?

Relative velocity is crucial in many scenarios, such as a boat crossing a river, an airplane flying in wind, or a person walking on a moving walkway. It involves considering the velocities of objects relative to different frames of reference.

32. What is the significance of Newton's First Law in understanding motion?

Newton's First Law, also known as the law of inertia, states that an object will remain at rest or in uniform motion unless acted upon by an external force. It explains why objects tend to stay in their current state of motion.

33. How do we interpret the sign (positive or negative) of velocity and acceleration?

The sign of velocity indicates direction of motion relative to the chosen coordinate system. For acceleration, a positive sign means the object is speeding up if moving in the positive direction, or slowing down if moving in the negative direction.

34. What is the relationship between kinematic equations and graphs of motion?

Kinematic equations mathematically describe the relationships between position, velocity, acceleration, and time. Graphs of motion visually represent these relationships, with slopes and areas corresponding to various kinematic quantities.

35. How does air resistance affect the motion of objects in real-world scenarios?

Air resistance opposes motion, causing objects to reach terminal velocity in free fall. It affects lighter objects more than heavier ones of the same size and shape, leading to deviations from ideal motion equations that assume no air resistance.

36. What is the concept of instantaneous speed and how does it differ from average speed?

Instantaneous speed is the speed of an object at a particular instant or point in time. It's calculated as the limit of average speed as the time interval approaches zero. Average speed considers the total distance traveled over a larger time interval.

37. How do we analyze motion when acceleration is not constant?

When acceleration is not constant, we can't use simple kinematic equations. Instead, we need to use calculus, breaking the motion into small intervals where acceleration can be approximated as constant, or use more advanced mathematical techniques.

38. What is the importance of vector addition in understanding complex motions?

Vector addition is crucial for analyzing motions that occur in multiple dimensions or when multiple forces act on an object. It allows us to combine different components of motion or forces to determine the resultant motion or net force.

39. How does the principle of superposition apply to motion?

The principle of superposition in motion states that when two or more motions occur simultaneously, their individual effects can be added vectorially to determine the resultant motion. This is particularly useful in analyzing complex motions.

40. What is the role of dimensional analysis in solving motion problems?

Dimensional analysis helps verify the correctness of equations and calculations in motion problems. It ensures that the units on both sides of an equation match and can help in deriving relationships between different physical quantities.

41. Can an object have constant speed but changing velocity?

Yes, this occurs when an object moves in a circular path at constant speed. The velocity is constantly changing because the direction of motion is changing, even though the speed remains the same.

42. What is uniform motion?

Uniform motion is when an object moves at a constant velocity (both constant speed and direction) in a straight line. There is no acceleration in uniform motion.

43. What causes objects to change their state of motion?

According to Newton's First Law, objects change their state of motion (or rest) when an unbalanced force acts upon them. This could be due to applied forces, friction, gravity, or other interactions.

44. How can an object have zero displacement but non-zero distance traveled?

This occurs when an object returns to its starting point after traveling along a path. For example, running around a circular track - the distance traveled is the circumference, but the displacement is zero.

45. What is the relationship between displacement, velocity, and acceleration?

Velocity is the rate of change of displacement with time, and acceleration is the rate of change of velocity with time. Mathematically, velocity is the first derivative of displacement, and acceleration is the second derivative.

46. What is free fall motion?

Free fall is the motion of an object under the influence of gravity alone, without air resistance. All objects in free fall near Earth's surface accelerate downward at approximately 9.8 m/s².

47. What is relative motion?

Relative motion is the motion of an object as observed from a particular frame of reference. The observed motion can change depending on the chosen reference frame.

48. What is the difference between scalar and vector quantities in motion?

Scalar quantities, like speed and distance, have only magnitude. Vector quantities, like velocity and displacement, have both magnitude and direction.

49. What is non-uniform motion?

Non-uniform motion occurs when an object's velocity changes over time, either in speed, direction, or both. It implies the presence of acceleration.

50. How do position, displacement, and distance differ?

Position is the location of an object relative to a reference point. Displacement is the change in position and has direction. Distance is the total length of the path traveled, regardless of direction.

51. How do initial conditions affect the motion of an object?

Initial conditions, such as starting position, velocity, and acceleration, determine how an object will move. They are crucial for predicting future positions and velocities using equations of motion.

52. How does motion in a straight line differ from circular motion?

Motion in a straight line involves movement along a single axis, with potential changes in speed but not direction. Circular motion involves constant change in direction (and thus velocity) even if speed remains constant.

53. How does understanding motion contribute to broader concepts in physics?

Understanding motion is fundamental to many areas of physics. It forms the basis for studying forces, energy, momentum, and more complex systems in classical and modern physics. Motion concepts are essential for fields ranging from engineering to astrophysics.