NEET Physics: Motion in One Dimension – Mechanics, Kinematics & Dynamics Notes

 

NEET Physics – Motion in One Dimension

Motion in One Dimension explained with Mechanics, Kinematics, Dynamics, and Frame of Reference for NEET aspirants.

Chapter 1: Basic Concepts of Mechanics (Complete Notes)

-Dr.Sanjaykumar Pawar 

---

1. What is Physics?

Physics is the branch of science that studies matter, energy, motion, and forces.

Example:

• Why does a ball fall?

• Why does a bike move?

• Why do planets revolve around the Sun?

All these are studied in Physics.

---

2. What is Mechanics?

Mechanics is the branch of Physics that studies the motion of objects and the forces causing that motion.

Simple Definition

Mechanics = Study of motion + causes of motion.

---

Mechanics is divided into two parts

              Mechanics
             /          \
      Kinematics      Dynamics

---

3. Kinematics

Definition

Kinematics is the branch of mechanics that studies motion without considering the force causing it.

It tells us

• Where the object is

• How fast it moves

• How far it moves

• How long it takes

But NOT why it moves.

Example

A car moves with speed 40 km/h.

Kinematics studies

✔ Speed

✔ Distance

✔ Time

✔ Displacement

It does NOT study engine force.

---

4. Dynamics

Definition

Dynamics studies motion along with the forces responsible for the motion.

It answers

Why does the object move?

Example

A football moves because a player kicks it.

Dynamics studies the force of the kick.

---

Difference Between Kinematics and Dynamics

Kinematics	Dynamics
Studies motion only	Studies motion + force
Force is ignored	Force is considered
Easier chapter	Uses Newton's Laws
Example: Speed	Example: Force

---

5. Frame of Reference

This is one of the most important concepts in NEET.

Definition

A Frame of Reference is a coordinate system attached to an observer from which measurements of position and time are made.

Simply,

It is the point from which an observer watches motion.

---

It contains

(1) Observer

Who is watching?

Example

You

Driver

Passenger

Teacher

---

(2) Space Coordinate

Where is the object?

Usually represented by

x-axis

y-axis

z-axis

---

(3) Time Coordinate

When is the object observed?

Measured using a clock.

---

Example

A train is moving.

Passenger says

"I am at rest."

A person standing on the platform says

"The train is moving."

Both are correct because their frames of reference are different.

---

Important Points

Motion depends on

✔ Observer

✔ Position

✔ Time

---

There is NO Absolute Motion

Motion is always relative.

There is nothing called

❌ Absolute Motion

❌ Absolute Rest

Everything depends upon the observer.

---

Example

You are sitting inside a moving bus.

With respect to

Seat → You are at rest.

Road → You are moving.

Both answers are correct.

---

6. Rest and Motion

Rest

An object is at rest if its position does not change with respect to the observer.

Example

Book lying on a table.

---

Motion

An object is in motion if its position changes with time with respect to an observer.

Example

Running car.

Flying bird.

Moving train.

---

Remember

Motion requires

✔ Observer

✔ Position

✔ Time

---

7. Point Object (Particle)

Very important for NEET.

Definition

A point object is an object whose size is very small compared to the distance travelled, so its dimensions can be ignored.

---

Example

Bike length = 2 m

Distance travelled = 500 km

Compared to 500 km,

2 m is negligible.

So bike is treated as a point object.

---

Another Example

Earth revolves around the Sun.

Earth diameter = 12,742 km

Distance from Sun = 150 million km

Compared to this huge distance,

Earth behaves like a point object.

---

When can an object be treated as a Point Object?

Ignore size when

Distance travelled ≫ Size of object

---

Example

Object	Distance	Point Object?
Car travelling 200 km	Yes	✔
Cricket ball moving 40 m	Yes	✔
Pencil moving 2 cm	No	✖

---

8. Position

Position tells where an object is located with respect to a chosen origin.

Example

If a boy stands 5 m to the right of the origin,

Position = +5 m

If he stands 3 m to the left,

Position = −3 m

---

9. Origin

Origin is the reference point from which distances are measured.

Usually represented by

O

Example

<------|------|------|------>

     -2    -1    O    +1   +2

---

10. Coordinate System

Used to locate objects.

One-dimensional (1D)

Only x-axis

Example

Train on straight track.

---

Two-dimensional (2D)

x-axis and y-axis

Example

Football ground.

---

Three-dimensional (3D)

x-axis

y-axis

z-axis

Example

Flying aeroplane.

---

Important NEET Concepts

Observer

Person who measures motion.

---

Coordinate

Shows position.

---

Time

Shows when motion occurs.

---

Motion depends on observer.

Always remember

Motion is Relative.

---

Frequently Asked NEET Facts

SI Unit of Distance

metre (m)

---

SI Unit of Time

second (s)

---

SI Unit of Speed

m/s

---

SI Unit of Force

Newton (N)

---

Previous Year NEET Concepts

Example 1

A passenger sitting inside a moving train is

A) Moving with respect to train

B) At rest with respect to train

C) Moving with respect to seat

D) None

Answer

✅ B

---

Example 2

A car moves from Delhi to Jaipur.

The car is treated as

A) Rigid body

B) Point object

C) Fluid

D) None

Answer

✅ B

---

Example 3

Motion is

A) Absolute

B) Relative

C) Constant

D) None

Answer

✅ B

---

Formula Sheet (This Topic)

There are no numerical formulas in this introductory topic. Focus on understanding the concepts.

---

One-Page Revision

Mechanics

• Study of motion and the causes of motion.

Kinematics

• Motion only.

• No force.

Dynamics

• Motion + force.

Frame of Reference

• Observer + coordinate system + time.

Motion

• Position changes with time relative to an observer.

Rest

• Position does not change relative to an observer.

Point Object

• Size is negligible compared to the distance travelled.

Key Rule

• There is no absolute rest or absolute motion; all motion is relative to the observer.

These notes provide a strong conceptual foundation for Motion in One Dimension, a high-weightage topic in the NEET Physics syllabus. 

Internal Links

1. Units and Measurements Notes for NEET
2. Vector and Scalar Quantities
3. Motion in Two Dimensions
4. Laws of Motion
5. Work, Energy and Power
6. System of Particles and Rotational Motion
7. Gravitation Notes
8. Oscillations and SHM
9. Mechanical Properties of Solids
10. Mechanical Properties of Fluids
11. Thermal Physics Complete Notes
12. Waves and Sound Notes
13. Complete NEET Physics Formula Sheet
14. NEET Physics PYQs Chapter-wise
15. Motion in One Dimension MCQs with Answers
16. Motion in One Dimension Numericals for NEET 
17. Motion in One Dimension Revision Notes
18. Class 11 Physics Complete Notes
19. NEET Physics Mock Tests
20. NEET Physics Study Plan

🔥 NEET Physics – Motion in One Dimension

Part 1 : Ultra-Hard NEET Numericals

Instructions

• Total Questions : 25
• Difficulty : NEET Advanced
• Use SI Units.
• Take g = 10 m/s² whenever required.
• Do not use calculator unless instructed.

---

Q1.

A car starts from rest and moves with a constant acceleration of 4 m/s² for 15 s. Calculate

1. Final velocity
2. Total displacement
3. Average velocity

Q2.

A train moving at 20 m/s accelerates uniformly to 50 m/s in 15 s. Find

1. Acceleration
2. Distance travelled

Q3.

A body travels

• 40 m East
• 30 m West
• 20 m East

Calculate

1. Total distance
2. Displacement

Q4.

A particle moves with velocity v = 5 + 2t where t is in seconds. Find

1. Velocity after 8 s
2. Displacement in first 8 s

Q5.

A ball is thrown vertically upward with speed 40 m/s. Calculate

1. Maximum height
2. Time to reach highest point
3. Total time of flight

Q6.

A runner completes

• First half distance at 10 m/s
• Second half distance at 15 m/s

Find average speed.

Q7.

A particle covers

• 100 m in North direction
• 100 m in East direction

Calculate

1. Distance
2. Displacement

Q8.

A car moving at 25 m/s stops uniformly in 5 seconds. Calculate

1. Retardation
2. Stopping distance

Q9.

Two cars move towards each other. Car A = 30 m/s Car B = 20 m/s Initially separated by 500 m. Find time to meet.

Q10.

A particle travels

• 2 hours at 40 km/h
• 3 hours at 60 km/h

Find

1. Total distance
2. Average speed

Q11.

A body starts from rest with acceleration 3 m/s² Find displacement in 12 seconds.

Q12.

A train moving at 72 km/h crosses a 300 m platform in 30 s. Find length of train.

Q13.

A cyclist increases speed uniformly from 5 m/s to 15 m/s over a distance of 100 m. Find acceleration.

Q14.

A body moves 10 m East 10 m North 10 m West Find displacement.

Q15.

A particle has velocity v = 20 − 5t Find

1. Time when particle stops
2. Distance travelled till then

Q16.

A stone falls freely from a tower. It reaches ground in 6 s. Find

1. Height of tower
2. Velocity on reaching ground

Q17.

A bus travels 80 km at 40 km/h and 120 km at 60 km/h. Find average speed.

Q18.

A particle moves according to s = 4t² + 3t Find velocity after 5 seconds.

Q19.

Two trains Length = 200 m each Speed = 15 m/s and 25 m/s move in opposite directions. Find time taken to cross each other.

Q20.

A particle covers first one-third distance with speed 10 m/s remaining distance with speed 20 m/s Find average speed.

Q21.

A body starts with velocity 15 m/s Acceleration 2 m/s² Find distance covered in 20 s.

Q22.

A particle moves 50 m East 120 m West 70 m East Calculate displacement.

Q23.

A train moving at 54 km/h crosses a man standing on platform in 12 seconds. Length of train?

Q24.

A particle starts from rest. Acceleration = 5 m/s² Find distance travelled during 4th second.

Q25. ⭐ NEET Challenge

A particle moves according to x = 5 + 4t + 2t² Find

1. Position after 6 s
2. Velocity after 6 s
3. Acceleration
4. Distance covered between 2 s and 6 s

Practice Rule

• Attempt all questions without looking at formulas.
• Write complete steps.
• Time yourself (45 minutes).
• Target Score : 25/25

End of Part 1
Next: Part 2 – Full NEET Mock Test (45 Questions)

🔥 Supplementary Part 2

Ultra-Hard Motion in One Dimension Numericals (Q26–Q50)

Instructions

• Difficulty: NEET Advanced
• Attempt without calculator.
• Take g = 10 m/s² unless otherwise stated.

---

Q26

A car accelerates uniformly from 10 m/s to 40 m/s in 12 seconds. Find:

1. Acceleration
2. Distance travelled

Q27

A particle moves with velocity v = 8 + 3t. Find displacement during first 10 seconds.

Q28

A train moving at 90 km/h crosses a pole in 18 s. Find length of train.

Q29

A ball is projected vertically upward with speed 50 m/s. Find:

1. Maximum height
2. Total time of flight

Q30

A body covers:

• 120 m at 6 m/s
• 180 m at 9 m/s

Find average speed.

Q31

Two cars move in the same direction. Car A = 18 m/s Car B = 24 m/s Initial gap = 240 m. Find time taken by B to overtake A.

Q32

A particle starts from rest with acceleration 4 m/s². Find distance travelled during the 8th second.

Q33

A cyclist slows uniformly from 12 m/s to rest in 6 s. Find stopping distance.

Q34

A particle moves:

• 40 m North
• 30 m East
• 40 m South

Find displacement.

Q35

Velocity equation: v = 24 − 4t Find:

1. Time to stop
2. Distance travelled

Q36

A freely falling stone reaches the ground with velocity 60 m/s. Find height of the tower.

Q37

A train of length 180 m crosses a bridge of length 420 m in 24 s. Find speed of train.

Q38

A body moves according to x = 3t² + 2t + 5. Find velocity at t = 8 s.

Q39

A car travels:

• 100 km at 50 km/h
• 150 km at 75 km/h

Find average speed.

Q40

Two trains of lengths 250 m and 150 m move in opposite directions at 18 m/s and 22 m/s. Find crossing time.

Q41

A particle starts from rest. Acceleration = 6 m/s². Find displacement after 15 seconds.

Q42

A ball is thrown downward from a building with velocity 15 m/s. It reaches ground in 5 s. Find height of building.

Q43

A particle covers one-fourth distance at 12 m/s and remaining distance at 24 m/s. Find average speed.

Q44

Position equation: s = 2t³ − 5t² + 8. Find velocity at t = 3 s.

Q45

A train moving at 54 km/h overtakes another moving at 36 km/h. Both trains are 150 m long. Find overtaking time.

Q46

A body starts with velocity 20 m/s and acceleration 3 m/s². Find velocity after travelling 150 m.

Q47

A particle moves:

• 100 m East
• 60 m West
• 20 m East
• 40 m West

Find:

1. Total distance
2. Displacement

Q48

A stone is thrown upward from a cliff of height 80 m with speed 30 m/s. Find time taken to hit the ground.

Q49

A particle has acceleration a = 4 m/s². Initial velocity = 6 m/s. Find displacement in first 12 s.

Q50 ⭐ NEET Challenge

Position equation: x = 10 + 6t + 3t² Find:

1. Position at t = 8 s
2. Velocity at t = 8 s
3. Acceleration
4. Distance travelled between 4 s and 8 s

---

Self Evaluation

Score	Performance
23–25	Excellent (NEET Top Rank Level)
18–22	Very Good
12–17	Good, Needs Practice
Below 12	Revise Theory & Formulae

End of Supplementary Part 2
Next: Part 3 – Full NEET Mock Test (45 Questions)

🔥 NEET Physics Mock Test

Motion in One Dimension (Part 3)

Total Questions : 45
Time : 45 Minutes
Marks : 180
Correct : +4
Wrong : −1

---

Section A (MCQs)

Q1. SI unit of displacement is

A) m/s
B) m
C) km
D) s

Q2. Distance is a

A) Vector
B) Scalar
C) Tensor
D) None

Q3. Velocity can become zero during upward motion of a projectile at

A) Highest point
B) Lowest point
C) Throughout
D) Never

Q4. Average velocity equals average speed when

A) Circular path
B) Straight line without changing direction
C) Closed path
D) Random motion

Q5. Which quantity may be zero even when distance is not zero?

A) Speed
B) Time
C) Displacement
D) Velocity

Q6. A body starts from rest. Initial velocity is

A) 1 m/s
B) 10 m/s
C) 0 m/s
D) −1 m/s

Q7. Uniform velocity means

A) Constant speed only
B) Constant velocity
C) Variable speed
D) Variable direction

Q8. Unit of acceleration

A) m
B) m/s
C) m/s²
D) km/h

Q9. Graph of uniform motion is

A) Straight line
B) Circle
C) Parabola
D) Hyperbola

Q10. Which is a vector?

A) Speed
B) Distance
C) Velocity
D) Time

Q11. A car moves 20 m East then 20 m West. Displacement is

A)40 m B)20 m C)0 D)10 m

Q12. Average speed is

A)Total Distance/Total Time B)Displacement/Time C)v²-u² D)None

Q13. Motion along straight line is called

A)Rectilinear B)Circular C)Rotational D)Projectile

Q14. Retardation is

A)Positive acceleration B)Negative acceleration C)Zero acceleration D)Infinite acceleration

Q15. Speedometer measures

A)Velocity B)Distance C)Instantaneous Speed D)Average Speed

Q16. Odometer measures

A)Speed B)Distance C)Acceleration D)Velocity

Q17. Motion is always

A)Absolute B)Relative C)Constant D)Uniform

Q18. A freely falling body has acceleration

A)g B)0 C)2g D)Depends on mass

Q19. Unit of velocity

A)m B)m/s C)m/s² D)km

Q20. Equation v=u+at is valid for

A)Variable acceleration B)Constant acceleration C)Circular motion D)Random motion

Q21. Which quantity is never negative?

A)Velocity B)Displacement C)Speed D)Acceleration

Q22. Area under velocity-time graph gives

A)Acceleration B)Distance/Displacement C)Speed D)Force

Q23. Slope of displacement-time graph gives

A)Acceleration B)Velocity C)Force D)Momentum

Q24. Slope of velocity-time graph gives

A)Displacement B)Acceleration C)Time D)Distance

Q25. A body moving with constant velocity has

A)Zero acceleration B)Maximum acceleration C)Infinite acceleration D)Variable acceleration

Q26. Graph of rest on displacement-time graph is

A)Horizontal line B)Vertical line C)Curve D)Circle

Q27. SI unit of time

A)Hour B)Second C)Minute D)Day

Q28. Which is scalar?

A)Velocity B)Acceleration C)Distance D)Displacement

Q29. Initial velocity symbol

A)s B)t C)u D)v

Q30. Final velocity symbol

A)u B)a C)v D)s

---

Section B (Assertion-Reason)

Q31. Motion is relative.
Reason: There is no absolute rest.

Q32. Average speed is always less than average velocity.
Reason: Speed is scalar.

Q33. Displacement may be zero while distance is not zero.
Reason: Distance is scalar.

Q34. Constant speed always means constant velocity.
Reason: Direction may change.

Q35. Uniform acceleration means equal change in velocity in equal intervals of time.

---

Section C (Numericals)

Q36. A body starts from rest with acceleration 5 m/s². Find velocity after 8 s.

Q37. A train moving at 20 m/s travels for 30 s. Find distance.

Q38. A body moves 60 m East then 80 m West. Find displacement.

Q39. A stone is dropped from height 45 m. Find time to reach ground.

Q40. Find average speed if a car travels 120 km in 2 hours.

Q41. Find displacement using s=ut+½at² where u=10 m/s, a=2 m/s², t=5 s.

Q42. Find acceleration if velocity changes from 10 m/s to 30 m/s in 4 s.

Q43. A train of length 180 m crosses a pole in 12 s. Find speed.

Q44. A ball is thrown upward with 20 m/s. Find maximum height.

Q45. A body moves with velocity equation v=6+2t. Find velocity after 8 s.

---

OMR Answer Sheet

Q	Ans	Q	Ans	Q	Ans
1	___	16	___	31	___
2	___	17	___	32	___
3	___	18	___	33	___
4	___	19	___	34	___
5	___	20	___	35	___
6	___	21	___	36	___
7	___	22	___	37	___
8	___	23	___	38	___
9	___	24	___	39	___
10	___	25	___	40	___
11	___	26	___	41	___
12	___	27	___	42	___
13	___	28	___	43	___
14	___	29	___	44	___
15	___	30	___	45	___

End of Part 3 – Full NEET Mock Test
Part 4: Detailed Answer Key & Step-by-Step Solutions

🔥 NEET Physics

Part 4 – Answer Key & Step-by-Step Solutions

---

Section A (MCQs)

Q	Answer	Q	Answer	Q	Answer
1	B	11	C	21	C
2	B	12	A	22	B
3	A	13	A	23	B
4	B	14	B	24	B
5	C	15	C	25	A
6	C	16	B	26	A
7	B	17	B	27	B
8	C	18	A	28	C
9	A	19	B	29	C
10	C	20	B	30	C

---

Section B (Assertion–Reason)

Question	Correct Option
31	A (Both true, Reason correctly explains)
32	D (Assertion false, Reason true)
33	B (Both true, Reason not correct explanation)
34	D (Assertion false, Reason true)
35	A (Both true, Reason correctly explains)

---

Section C (Numericals)

Q36

Given u = 0 m/s a = 5 m/s² t = 8 s

v = u + at
v = 0 + 5 × 8

Answer = 40 m/s

Q37

Distance = Speed × Time
= 20 × 30

Answer = 600 m

Q38

East = +60 West = -80

Displacement = 60 - 80 = -20 m

Answer = 20 m West

Q39

s = 45 m u = 0 g =10

45 = 5t²
t² =9
t =3 s

Answer = 3 s

Q40

Average Speed =120/2

Answer =60 km/h

Q41

s = ut + ½at²
=10×5 + ½×2×25
=50+25

Answer =75 m

Q42

a=(30−10)/4
=20/4

Answer =5 m/s²

Q43

Speed =180/12

Answer =15 m/s

Q44

Maximum Height H=u²/2g
=20²/(20)
=20 m

Answer =20 m

Q45

v=6+2t
=6+16
Answer =22 m/s

---

Score Analysis

Marks	Performance
170–180	Outstanding ⭐⭐⭐⭐⭐
150–169	Excellent
120–149	Very Good
90–119	Good
Below 90	Needs Revision

Common Mistakes in NEET Motion in One Dimension

• Confusing distance with displacement.
• Using average velocity instead of average speed.
• Incorrect sign convention (+ and -).
• Using wrong kinematic equation.
• Mixing km/h and m/s units.
• Ignoring direction in vector quantities.
• Calculation mistakes in free-fall problems.

✔ Part 4 Completed

Next: Part 5 – 100 Previous Year Questions (NEET + AIIMS + JIPMER) with Detailed Solutions

🔥 Part 5

Previous Year Question Bank (NEET / AIPMT / AIIMS Style)

This section contains NEET-style questions inspired by previous exam patterns. They are designed for practice and concept building.

---

Q1. A body moves 10 m east and then 10 m west. What is its displacement?

A) 20 m   B) 10 m   C) 0 m   D) 5 m

Answer: C (0 m)

Q2. Which of the following is a scalar quantity?

A) Velocity B) Acceleration C) Distance D) Displacement

Answer: C

Q3. SI unit of acceleration is

A) m B) m/s C) m/s² D) km/h

Answer: C

Q4. A car starts from rest with acceleration 4 m/s². Find velocity after 5 s.

Answer: 20 m/s

Q5. A train moving at 25 m/s crosses a pole in 8 s. Find length of train.

Answer: 200 m

Q6. A body falls freely for 4 s. Find its velocity on reaching the ground.

Answer: 40 m/s

Q7. Average speed is defined as A) Distance / Time B) Displacement / Time C) Velocity / Time D) None

Answer: A

Q8. Which graph represents uniform motion?

Answer: Straight line on displacement–time graph

Q9. A body moves with constant velocity. Its acceleration is

Answer: Zero

Q10. A stone is thrown upward with speed 30 m/s. Find maximum height.

Answer: 45 m

---

🔥 PYQ Practice Set (Without Answers)

1. A body covers 240 m in 30 s. Find average speed.
2. A car accelerates from 10 m/s to 30 m/s in 5 s. Find acceleration.
3. Define displacement with one example.
4. Differentiate between speed and velocity.
5. A particle moves according to x = 4 + 5t + 2t². Find velocity at t = 6 s.
6. A train of length 250 m crosses a bridge of length 350 m in 24 s. Find speed.
7. A freely falling body reaches the ground in 8 s. Find height.
8. State any two differences between distance and displacement.
9. Find stopping distance of a car moving at 30 m/s if retardation is 5 m/s².
10. Find average speed if equal distances are covered at 20 km/h and 30 km/h.

---

🔥 Formula Revision Sheet

• v = u + at
• s = ut + ½at²
• v² = u² + 2as
• Average Speed = Total Distance / Total Time
• Average Velocity = Total Displacement / Total Time
• Distance = Speed × Time
• Acceleration = (v − u) / t

---

🎯 NEET Rapid Revision

• Motion is relative.
• Distance is scalar.
• Displacement is vector.
• Speed is scalar.
• Velocity is vector.
• Acceleration can be positive or negative.
• Retardation = Negative acceleration.
• Slope of displacement–time graph = Velocity.
• Slope of velocity–time graph = Acceleration.
• Area under velocity–time graph = Displacement.

★★★★★ Congratulations! ★★★★★ You have completed the complete practice package for Motion in One Dimension

Recommended Next Chapter: Motion in a Plane (2D Motion & Projectile Motion)

Motion in One Dimension Notes for NEET 2026 | Distance & Displacement MCQs with Solutions

 Motion in One Dimension – Rest, Motion & Frame of Reference (NEET Notes) 

Motion in One Dimension – Complete NEET Physics Notes on Frame of Reference, Distance, Displacement, Rest and Motion.

1. Can the Distance Between Two Places Be Fixed?

Example

Question: What is the distance between City A and City B?

Answer: This is an incomplete (incorrectly framed) question because the distance depends on the path or route taken.

For example:

• Route 1 = 1050 km
• Route 2 = 1510 km

Therefore, distance depends on the path followed.

Important: Always specify the route while asking about distance.

---

2. Frame of Reference

Definition

A frame of reference is a place or point from where we observe the position or motion of an object.

The person who makes the observation is called the observer.

Example

A student is standing on the roadside and watching a moving bus.

• Road = Frame of reference
• Student = Observer

---

3. Position

Definition

The position of an object is its location with respect to a frame of reference.

Example

A bicycle is parked 10 m from a tree.

Here,

• Tree = Frame of reference
• Bicycle = Object

---

4. Rest

Definition

An object is said to be at rest if its position does not change with time with respect to the chosen frame of reference.

Example

A school bag kept on a classroom desk is at rest with respect to the desk.

Position
  ^
  |
  |──────────────
  |
  +---------------------> Time

Position remains constant.

---

5. Motion

Definition

An object is said to be in motion if its position changes with time with respect to the chosen frame of reference.

Example

A car moving on a highway is in motion with respect to the road.

Position
  ^
  |        /
  |      /
  |    /
  +---------------------> Time

Position changes with time.

---

Relative Nature of Rest and Motion

Rest and motion are relative terms, not absolute.

They depend on the frame of reference.

Example

Suppose:

• Student A is sitting inside a moving bus.
• Student B is sitting beside Student A.
• A traffic police officer is standing on the roadside.

Then:

• Student A is at rest with respect to Student B.
• Student B is at rest with respect to Student A.
• Student A is in motion with respect to the traffic police officer.
• Student B is also in motion with respect to the traffic police officer.

Thus, the same object can be at rest for one observer and in motion for another observer.

---

Important NEET Points

• Frame of Reference: Place from where observation is made.
• Observer: Person making the observation.
• Position: Location of an object with respect to the frame of reference.
• Rest: Position does not change with time.
• Motion: Position changes with time.
• Distance depends on the path taken.
• Rest and motion are relative concepts.
• There is no absolute rest or absolute motion in the universe.

---

NEET Quick Revision

• Frame of Reference → Point from where observation is made.
• Observer → Person who observes.
• Position → Location relative to the reference point.
• Rest → Position remains unchanged with time.
• Motion → Position changes with time.
• Distance → Depends on the path followed.
• Rest and Motion → Relative, not absolute. 

Motion in One Dimension – Distance and Displacement (NEET Notes)

1. Observer Always Assumed to be at Rest

Definition

While studying motion, the observer is always assumed to be at rest with respect to the chosen frame of reference.

Example

A student is sitting inside a moving bus and asks,

"Sir, when will Delhi come?"

The teacher replies,

"Delhi is not coming. Our bus is moving towards Delhi."

Although it appears that Delhi is coming closer, actually the bus is moving, while Delhi is at rest with respect to the Earth.

Important Point

• Motion is always described with respect to an observer.
• The observer is usually considered to be at rest.

---

2. Distance

Definition

Distance is the actual length of the path travelled by an object.

OR

Distance is the total path covered by an object during its motion.

Formula

Distance = Actual Path Length

---

Characteristics of Distance

• It depends on the path taken.
• It is a Scalar Quantity (only magnitude, no direction).
• It is always positive or zero.
• It cannot be negative.
• SI Unit = metre (m).
• It is always greater than or equal to displacement.
• Scalar quantities are added by simple algebraic addition.

---

Example 1

A person walks

• 3 m forward
• then 4 m forward

Distance = 3 + 4 = 7 m

---

Example 2

A person walks along three different paths between the same two points.

Path A = 10 m

Path B = 15 m

Path C = 18 m

Distance depends on which path is chosen.

---

3. Displacement

Definition

Displacement is the shortest straight-line distance between the initial position and the final position of an object.

OR

Displacement is the change in the position of an object.

---

Formula

Displacement = Final Position − Initial Position

---

Characteristics of Displacement

• It depends only on the initial and final positions.
• It does not depend on the path taken.
• It is a Vector Quantity (has magnitude and direction).
• It can be positive, negative, or zero.
• SI Unit = metre (m).
• To calculate displacement, only the initial position and final position are required.

---

Example 1

A person walks

• 3 m east
• then 4 m east

Distance = 7 m

Displacement = 7 m east

Since there is no change in direction,

Distance = Displacement

---

Example 2

A person walks

• 3 m east
• then 4 m west

Distance = 3 + 4 = 7 m

Displacement = 1 m west

Here,

Distance > Displacement

---

Example 3

A person starts from point A, walks around a circular park, and returns to point A.

Distance = Circumference of the park

Displacement = 0

Because the initial and final positions are the same.

---

4. Relation Between Distance and Displacement

Case 1: Straight-Line Motion (No Change in Direction)

Example

3 m → + 4 m →

Distance = 7 m

Displacement = 7 m

Distance = Displacement

---

Case 2: Motion with Change in Direction

Example

3 m → then 4 m ←

Distance = 7 m

Displacement = 1 m

Distance > Displacement

---

Important NEET Points

Distance	Displacement
Actual path length	Shortest straight-line distance
Scalar quantity	Vector quantity
Depends on path	Does not depend on path
Always positive or zero	Can be positive, negative, or zero
Cannot be negative	Can be negative
Distance ≥ Displacement	Displacement ≤ Distance
Unit = metre (m)	Unit = metre (m)

---

NEET Quick Revision

• Observer → Usually assumed to be at rest.
• Distance → Actual path travelled.
• Displacement → Shortest straight-line distance between initial and final positions.
• Distance depends on path.
• Displacement depends only on initial and final positions.
• Distance is a scalar quantity.
• Displacement is a vector quantity.
• Distance is always greater than or equal to displacement.
• Distance = Displacement only when the object moves in a straight line without changing direction.

Motion in One Dimension - Distance & Displacement (NEET Level)

Concept Questions with Solutions

Q1. Which of the following is always true for a moving object?
A) Distance = |Displacement|
B) Distance < |Displacement|
C) Distance ≥ |Displacement|
D) Distance ≤ |Displacement|

Answer: C) Distance ≥ |Displacement|
Explanation: Distance is actual path length, while displacement is shortest straight-line distance between initial and final points. So distance is always greater than or equal to displacement.

Q2. For motion in 1-D without change in direction, which is correct?
A) Distance = |Displacement|
B) Distance > |Displacement|
C) Distance < |Displacement|
D) None

Answer: A) Distance = |Displacement|
Explanation: When motion is in a straight line without reversing direction, actual path equals shortest path, so distance equals magnitude of displacement.

Q3. A person walks 4 m east and then 3 m east. Find distance and displacement.

Answer:
Distance = 4 + 3 = 7 m
Displacement = 7 m east
Explanation: Both motions are in same direction, so distance = displacement.

Q4. A person walks 6 m east and 4 m west. Find distance and displacement.

Answer:
Distance = 6 + 4 = 10 m
Displacement = 2 m east
Explanation: Distance adds total path. Displacement = final - initial = 6 - 4 = 2 m east.

Q5. Why is displacement a vector quantity?

Answer: Because displacement has both magnitude and direction.
Explanation: It depends on initial and final positions and includes direction (positive or negative in 1D).

Q6. Can distance be negative?

Answer: No.
Explanation: Distance is scalar and represents actual path length, so it is always positive or zero.

Q7. A body returns to its starting point after moving in a circle. Find distance and displacement.

Answer:
Distance = circumference of circle
Displacement = 0
Explanation: Final position = initial position, so displacement is zero but path is not zero.

Q8. What is frame of reference?

Answer: It is the point or system from which an observer measures position or motion.
Explanation: Motion is always relative to a chosen observer.

Q9. Why is motion relative?

Answer: Because it depends on the observer.
Explanation: An object may appear at rest for one observer and in motion for another.

Q10. A car moves 15 m straight without changing direction. Find distance and displacement.

Answer:
Distance = 15 m
Displacement = 15 m
Explanation: Straight-line motion without change in direction makes distance equal to displacement.

Key Formulas

• Distance = Actual path length
• Displacement = Final position - Initial position
• |Displacement| ≤ Distance

Important Points

• Distance is scalar
• Displacement is vector
• Distance depends on path
• Displacement depends only on endpoints

Q11. A person walks 3 m north, then 4 m east. Find distance and displacement.

Answer:
Distance = 3 + 4 = 7 m
Displacement = √(3² + 4²) = √25 = 5 m (north-east direction)

Explanation:
Distance is total path length (scalar), so we simply add.
Displacement is shortest straight-line distance, so we use Pythagoras theorem because motion is at right angle.

Q12. A body moves 10 m forward and then 10 m backward. Find distance and displacement.

Answer:
Distance = 10 + 10 = 20 m
Displacement = 0 m

Explanation:
The object returns to its starting point, so final position = initial position.
Hence displacement is zero but distance is non-zero.

Q13. Which quantity can be zero even if an object moves? A) Distance B) Speed C) Displacement D) Time

Answer: C) Displacement

Explanation: If an object returns to its starting point, displacement becomes zero, but it still covers some distance.

Q14. A student says "Delhi is coming closer while we are in a train". Is this correct?

Answer: No, it is incorrect.

Explanation: Delhi is at rest with respect to Earth. The train is moving towards Delhi. Motion depends on frame of reference.

Q15. A particle moves in a straight line 8 m east and then 3 m west. Find displacement.

Answer:
Displacement = 8 - 3 = 5 m east

Explanation: Direction matters in displacement. East is positive, west is negative in 1D motion.

Q16. Why is distance always greater than or equal to displacement?

Answer:
Because distance is actual path and displacement is shortest path.

Explanation: Any curved or back-and-forth motion increases path length, so distance ≥ displacement always.

Q17. A car moves in a circular path and completes half a circle. Radius = 7 m. Find displacement.

Answer:
Displacement = diameter = 2 × 7 = 14 m

Explanation: In half circle, initial and final points are opposite ends of diameter.

Q18. Can displacement be greater than distance? A) Yes B) No

Answer: B) No

Explanation: Displacement is shortest distance, so it can never exceed actual path length.

Q19. A boy runs 5 m east, 5 m west, 5 m east again. Find distance and displacement.

Answer:
Distance = 5 + 5 + 5 = 15 m
Displacement = 5 m east

Explanation: Total path is added for distance, but final position is 5 m east of start.

Q20. Define observer in motion study.

Answer: The person who measures or observes the motion of an object is called an observer.

Explanation: All motion is described relative to the observer (frame of reference).

Q21. A particle moves 12 m north, then 5 m south. Find distance and displacement.

Answer:
Distance = 12 + 5 = 17 m
Displacement = 12 - 5 = 7 m north

Explanation:
Distance is total path length (scalar).
Displacement depends on direction, so we subtract opposite directions.

Q22. A body moves 6 m east, then 8 m north. Find displacement.

Answer:
Displacement = √(6² + 8²) = √(36 + 64) = √100 = 10 m (north-east)

Explanation:
Motion is at right angle, so we apply Pythagoras theorem.

Q23. If displacement is zero, what can we say about motion?

Answer: The object has returned to its initial position.

Explanation:
Even if the object moves, if final position = initial position, displacement becomes zero.

Q24. A car travels 20 m in a straight line. What is the relationship between distance and displacement?

Answer:
Distance = Displacement = 20 m

Explanation:
In straight-line motion without changing direction, path length equals shortest distance.

Q25. Which quantity gives only magnitude but no direction? A) Displacement B) Distance C) Velocity D) Acceleration

Answer: B) Distance

Explanation:
Distance is scalar, so it has only magnitude and no direction.

Q26. Can distance ever be negative?

Answer: No.

Explanation:
Distance is actual path length, so it is always positive or zero.

Q27. A person walks 10 m east and 10 m west. What is displacement?

Answer: 0 m

Explanation:
Final position is same as initial position, so displacement is zero.

Q28. What is the SI unit of displacement?

Answer: metre (m)

Explanation:
Displacement is a length quantity, so its SI unit is metre.

Q29. A student says “distance and displacement are always equal”. Is this correct?

Answer: No.

Explanation:
They are equal only in straight-line motion without change in direction.

Q30. A particle moves in a square path of side 4 m and returns to starting point. Find distance and displacement.

Answer:
Distance = 4 + 4 + 4 + 4 = 16 m
Displacement = 0 m

Explanation:
Distance is total perimeter, but displacement is zero because initial and final positions are same.

Q31. A car moves 18 m east and then 24 m north. Find displacement.

Answer:
Displacement = √(18² + 24²) = √(324 + 576) = √900 = 30 m (north-east)

Explanation:
Since motion is in two perpendicular directions, we use Pythagoras theorem to find shortest distance.

Q32. A body moves 15 m south and 15 m north. Find distance and displacement.

Answer:
Distance = 15 + 15 = 30 m
Displacement = 0 m

Explanation:
The object returns to its starting point, so displacement is zero.

Q33. Which statement is correct? A) Distance can be negative B) Displacement is always positive C) Distance is always ≥ |Displacement| D) Displacement is scalar

Answer: C) Distance is always ≥ |Displacement|

Explanation:
Distance is actual path length and cannot be less than shortest straight-line distance.

Q34. A student walks 7 m east, 7 m east, and 7 m west. Find displacement.

Answer:
Displacement = (7 + 7 - 7) = 7 m east

Explanation:
Take east as positive and west as negative, then add algebraically.

Q35. What is a frame of reference?

Answer: A system or point from which an observer measures position and motion.

Explanation:
Motion is always relative to a chosen reference point or observer.

Q36. A bus moves forward and a passenger feels stationary inside. Why?

Answer: Because both passenger and bus are in same frame of reference.

Explanation:
Relative motion inside the bus is zero, so passenger feels at rest.

Q37. A person completes one full circular path. What is displacement?

Answer: 0 m

Explanation:
Initial and final positions are same, so displacement is zero.

Q38. Which is vector quantity? A) Distance B) Speed C) Displacement D) Time

Answer: C) Displacement

Explanation:
Displacement has both magnitude and direction.

Q39. A body moves 9 m east and 12 m west. Find distance.

Answer: 21 m

Explanation:
Distance is total path length, so we add magnitudes.

Q40. Find displacement for Q39.

Answer: 3 m west

Explanation:
Net movement = 12 - 9 = 3 m towards west.

Q41. A particle moves 10 m east, 6 m north, and 10 m west. Find distance and displacement.

Answer:
Distance = 10 + 6 + 10 = 26 m
Displacement = 6 m north

Explanation:
Distance is total path length (scalar), so we add all parts.
East and west cancel each other (10 m east and 10 m west), leaving only 6 m north as net displacement.

Q42. A body moves in a straight line 25 m forward and then 25 m backward. Find displacement.

Answer: 0 m

Explanation:
Final position is same as initial position, so displacement becomes zero.

Q43. Which quantity depends on path taken? A) Displacement B) Position C) Distance D) Velocity

Answer: C) Distance

Explanation:
Distance depends on actual route followed, so different paths give different values.

Q44. A student says “displacement is always positive”. Is this correct?

Answer: No.

Explanation:
Displacement can be positive, negative, or zero depending on direction in 1-D motion.

Q45. A car moves 50 m straight without changing direction. What is true? A) Distance > Displacement B) Distance < Displacement C) Distance = Displacement D) Distance = 0

Answer: C) Distance = Displacement

Explanation:
In straight-line motion without reversing direction, path length equals shortest distance. 

Internal Links

• Units and Measurements Notes 

• Physical Quantities: Scalars and Vectors

 • Kinematics Complete Notes

 • Position, Distance and Displacement

 • Speed, Velocity and Acceleration

 • Graphs in Motion (Position-Time & Velocity-Time) 

• Relative Motion Explained

 • NCERT Class 11 Physics Chapter 3 Notes 

• NEET Physics Mock Tests

 • NEET Physics Previous Year Questions 

• Motion in a Straight Line Numericals 

• Laws of Motion Notes

 • Projectile Motion Notes

 • Circular Motion Basics

 • Physics Formula Sheet for NEET