Distance, Displacement, Speed, and Velocity
Understand the differences between distance and displacement, and between speed and velocity, including how to calculate average speed and average velocity in various scenarios.
Why this shows up in the exam
NEET tests your ability to distinguish and compute these fundamental quantities in different types of motion.
How NEET tests this
Learn the idea
Distance is the total length of the path travelled (scalar) while displacement is the straight‑line vector from start to finish. Speed uses distance/time, velocity uses displacement/time – the same formula but with a direction.
🧠 Memory hook: Distance = road‑trip length, Displacement = crow's straight flight; Speed = how fast you drive, Velocity = how fast you drive and which way you point.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- Distance (path length) is a scalar quantity
- Displacement is a vector quantity having magnitude and direction
- Speed = total distance ÷ total time (scalar)
- Velocity = net displacement ÷ total time (vector)
- Average speed = Σ distance / Σ time
- Average velocity = net displacement / Σ time
How to approach it
- 1Read the question and decide whether it asks for a scalar (distance, speed) or a vector (displacement, velocity)
- 2Calculate total distance travelled and total time; also find net displacement if required
- 3Apply speed = distance/time or velocity = displacement/time using the appropriate sign convention for 1‑D motion
- 4Check the answer’s units and sign (positive/negative for direction)
Worked example — watch it click
Assertion A: The magnitude of the displacement for a course of motion may be zero. Reason R: The path length for the corresponding course of motion is zero.
- A)If both assertion and reason are true, and reason is the correct explanation of assertion.
- B)If both assertion and reason are true, but reason is not the correct explanation of assertion.
- ✅If assertion is true, but reason is false.
- D)If both assertion and reason are false.
The concept behind this problem
The worked example checks whether you know that a zero displacement does not force the path length to be zero, i.e., the reason given is incorrect.
Step by step
- 1Assertion A is true: displacement can be zero for a closed path (e.g., circular motion returning to start).
- 2Reason R is false: when displacement is zero, the path length is NOT zero—the object has traveled some distance along the closed path.
- 3Path length is zero only if the object never moved.
- 4R does not explain A.
Watch out
Thinking that zero displacement implies the object has not moved at all, so the path length must be zero.
Common slip-ups that cost marks
- •Confusing distance with displacement – a closed loop has zero displacement but non‑zero distance
- •Using average speed formula for average velocity or vice‑versa
- •Ignoring direction sign in one‑dimensional problems, leading to wrong velocity sign
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Practise it
These are real questions from past NEET papers that test this exact idea.
Which of the following is a one dimensional motion?
Push further
More challenging7 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.
A particle moves from position (2m, 3m) to (5m, 7m) in 2 seconds. What is the magnitude of its average velocity?
More from Kinematics
Equations of Motion and Uniform Acceleration
Learn the kinematic equations for uniformly accelerated motion, including applications to free fall, retardation, and calculation of distance in specific time intervals.
Projectile Motion
Study the motion of projectiles, including the independence of horizontal and vertical components, trajectory equations, maximum height, and the effect of initial conditions.
Relative Velocity and Motion Analysis
Explore how to determine the velocity of one object relative to another and analyze motion from different reference frames, including periodic motion.
Position, Path Length, and Displacement
For one-dimensional motion, displacement over an interval is Delta x = x_f - x_i and may be positive, negative, or zero. Distance is the non-negative path length, so distance is always at least |Delta x|.
Speed and Velocity
Instantaneous velocity is the signed rate v = dx/dt, while instantaneous speed is |v|. In one dimension the sign of v identifies motion along or opposite the positive axis.
Average Speed and Average Velocity
Over elapsed time Delta t, average speed equals total distance/Delta t and average velocity equals Delta x/Delta t. For equal distances the relevant mean of speeds is harmonic, not arithmetic.