Measurement of Length and Motion – Short Answer Type Questions
CBSE Class 6 Science — Chapter 5: Measurement of Length and Motion
50 Short Answer Type Questions with clear answers — NCERT-aligned for CBSE Class 6 revision and board exam practice.
50 Short Answer Q&A — Topic-wise
Answers are concise, accurate and follow NCERT concepts for easy learning.
Units & Instruments (Questions 1–12)
1. Define length.
Length is the measurement of how long or short an object is, measured from one end to the other.
2. What is the SI unit of length?
The SI unit of length is the metre (m).
3. Convert 250 cm into metres.
250 cm = 250 ÷ 100 = 2.5 m.
4. How many millimetres are there in 7 cm?
1 cm = 10 mm, so 7 cm = 70 mm.
5. When would you use a measuring tape instead of a ruler?
When measuring long or curved objects (e.g., rope, cloth) where a flexible tape is needed.
6. What is a trundle wheel used for?
A trundle (measuring) wheel is used to measure long distances by rolling it along the ground.
7. Why is it important to use the correct unit with a measurement?
Units tell what the number represents; without units the measurement is meaningless and can be misinterpreted.
8. State two common units smaller than a metre.
Centimetre (cm) and millimetre (mm).
9. State two common units larger than a metre.
Kilometre (km) and hectometre (hm) — km is commonly used for long distances.
10. What is the purpose of the zero mark on a ruler?
The zero mark is the reference starting point to measure from; starting from zero gives accurate readings.
11. Give an example of when to use millimetres.
Measuring small objects like the diameter of a pencil lead or small electronic components.
12. What could cause an inaccurate reading with a tape measure?
Sagging or bending of the tape, not holding it straight, or reading from the wrong mark.
Measuring Techniques (13–22)
13. Describe how to measure the length of a book using a ruler.
Place the book along the ruler with one edge at the zero mark and read the measurement at the other edge.
14. How do you measure the length of a curved string?
Lay the string along the ruler in straight segments or use a tape; alternatively, mark on a thread and measure straightened thread with a ruler.
15. Why should measurements be repeated?
Repeating reduces random errors and provides a more reliable average value.
16. What is an estimated measurement?
An approximate reading taken when the exact value falls between two marks; estimate to nearest small division.
17. How to read a measurement if object end falls between two marks?
Estimate the fraction of the division and record the value with the unit (e.g., 4.7 cm).
18. How should a ruler be aligned to measure accurately?
Keep it straight and parallel to the object, with zero mark at one end of the object.
19. How to measure the diagonal of a rectangle?
Place ruler from one corner to the opposite corner and read the length along the diagonal.
20. What to do when the object is longer than the ruler?
Measure in parts and add the lengths, or use a measuring tape or metre scale.
21. How to ensure a measuring tape gives an accurate reading?
Keep it taut, straight, and aligned with the object; ensure the tape start point is correctly placed.
22. What is the advantage of using a digital measuring tool?
Digital tools give quick, precise readings and reduce human reading errors.
Concepts of Motion (23–32)
23. Define motion in simple words.
Motion is when an object changes its position with time.
24. Give two examples of motion.
A bicycle moving on road; a falling leaf from a tree.
25. What is distance?
Distance is the total path length an object covers during motion.
26. What is displacement (introductory)?
Displacement is the straight-line distance from the starting point to the final point along with direction (introduced simply in higher classes).
27. What instrument can measure time for motion experiments?
A stopwatch or a clock can be used to measure time intervals.
28. Why is time important in describing motion?
Because motion is change of position with time; time helps quantify how fast or slow the motion is.
29. What does the path of an object mean?
The route followed by the object during motion; it can be straight or curved.
30. How is rest different from motion?
An object is at rest if its position does not change with time; in motion if its position changes.
31. What is periodic motion? Give an example.
Motion that repeats itself after equal intervals of time, e.g., a child on a swing (simple example).
32. Is walking from home to school motion? Explain briefly.
Yes, because the person changes position over time as they move from home to school.
Speed — Basic Calculations (33–42)
33. Define speed.
Speed is the distance covered per unit time; it shows how fast an object is moving.
34. Give the formula for speed.
Speed = Distance ÷ Time (v = d / t).
35. A car covers 150 km in 3 hours. What is its speed?
Speed = 150 km ÷ 3 h = 50 km/h.
36. A runner completes 200 m in 25 s. Find speed in m/s.
Speed = 200 m ÷ 25 s = 8 m/s.
37. How to calculate average speed for a trip with different segments?
Add total distance of all segments and divide by total time taken for the whole trip.
38. Convert 5 m/s into km/h. (Hint: multiply by 3.6)
5 m/s × 3.6 = 18 km/h.
39. Convert 90 km/h into m/s. (Hint: divide by 3.6)
90 ÷ 3.6 = 25 m/s.
40. If a toy car covers 2 m in 1 s then 4 m in 2 s, what is its average speed over the whole motion?
Total distance = 2 + 4 = 6 m; total time = 1 + 2 = 3 s; average speed = 6 ÷ 3 = 2 m/s.
41. Why must units be consistent when calculating speed?
Because mixing units (e.g., metres with hours) gives incorrect numerical results; convert to consistent units first.
42. What units are commonly used for speed in school problems?
Metres per second (m/s) and kilometres per hour (km/h).
Practical Activities & Observations (43–50)
43. Describe a simple classroom activity to measure speed.
Measure a fixed distance (e.g., 10 m), let a toy car travel it, use a stopwatch to time the motion and calculate speed = distance/time.
44. How can you measure the length of a curved path on paper?
Use a thread to trace the curve, straighten the thread and measure its length with a ruler.
45. What should you record when doing motion experiments?
Record measured distances, time taken, units used, and any observations or repeated trial values.
46. How does repeating trials help in experiments?
Repeating gives multiple readings to average, reducing the effect of random errors and improving accuracy.
47. Suggest a way to measure long ground distance in school grounds.
Use a trundle wheel or measuring tape, or measure in segments with a metre scale and add them.
48. What is a common error students make while measuring with a ruler?
Starting from the ruler's edge instead of the zero mark or not keeping the ruler straight.
49. How to convert 3000 m to km?
3000 m = 3000 ÷ 1000 = 3 km.
50. Why are units and clear recording important in science experiments?
They ensure results are understandable, comparable, and reproducible by others.