Motion and Measurement of Distances

Long ago people travelled on foot or used animals, boats and carts with wheels; today we use trains, cars, ships and aeroplanes. In this chapter you will learn that measuring means comparing an unknown quantity with a known fixed quantity called a unit. Early people used handspans, cubits, footsteps and arm lengths, but these vary from person to person, so standard units were needed. The International System of Units (SI units) uses the metre as the unit of length, with 1 m = 100 cm, 1 cm = 10 mm and 1 km = 1000 m. The chapter teaches the correct way to measure length: place the scale along the object, start from a clear mark if the zero is broken, and keep your eye directly above the point being read. You will measure curved lines using a thread. Finally, you will study motion, a change in position with time, and its types: rectilinear motion along a straight line, circular motion along a circle, and periodic motion that repeats after fixed intervals, like a swinging pendulum.

Detailed Worksheet: Motion and Measurement of Distances Section A - Definitions (10 marks) 1. What is measurement? What is a unit? (2 marks) 2. Why are handspan and cubit not reliable units of length? (2 marks) 3. What is the SI unit of length? Write the relation between km, m, cm and mm. (2 marks) 4. Define motion. How can we say an object is in motion? (2 marks) 5. Define rectilinear, circular and periodic motion with one example of each. (2 marks) Section B - Calculations and Applications (15 marks) 6. Convert: (i) 2.5 km into m (ii) 75 cm into m (iii) 425 mm into cm (iv) 3 m 20 cm into cm (v) 1500 m into km (vi) 6.5 cm into mm. (3 marks) 7. A scale with a broken zero end is used to measure a pencil. One end of the pencil is at the 2.0 cm mark and the other end is at the 15.4 cm mark. (i) Find the length of the pencil. (ii) Explain why we should not start from a broken edge. (iii) Where should the eye be placed while reading the scale? (3 marks) 8. The height of a person is 1.65 m. Express it in cm and mm. A tree is 15 times the person's height; find its height in metres. (3 marks) 9. A student's handspan is 16 cm. A table is measured as 9 handspans long. (i) Find the length in cm. (ii) If the teacher's handspan is 20 cm, how many of her handspans would the table be? (iii) Why are the two numbers different? (3 marks) 10. A wheel of a cycle has a circumference of 2 m. (i) How far does the cycle move in 50 rotations of the wheel? (ii) How many rotations are needed to cover 1 km? (iii) Name the types of motion of the wheel and of the cycle. (3 marks) Section C - Diagrams (10 marks) 11. Draw a diagram showing the correct and incorrect positions of the eye while reading a scale placed along an object. Label the correct position and explain why the others give errors. (4 marks) 12. Draw a curved line of about 10 cm and show how you would measure it using a thread and a scale. Write the steps. (3 marks) 13. Draw simple sketches to show rectilinear motion (a car on a straight road), circular motion (a stone tied to a string) and periodic motion (a swinging pendulum), with arrows showing the direction. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. A sewing machine has a wheel that turns and a needle that moves up and down. (i) Name the type of motion of the wheel. (ii) Name the type of motion of the needle. (iii) Can an object have two types of motion at the same time? Give an example. (iv) What type of motion does the Earth have around the Sun? (5 marks) 15. Five students measured the length of the same desk with a metre scale and got 120.2 cm, 120.4 cm, 125.0 cm, 120.3 cm and 120.1 cm. (i) Which reading is likely wrong? (ii) Give two possible reasons for the error. (iii) Find the average of the other four readings. (iv) Why is it useful to take several readings? (5 marks) 16. A train is moving and a passenger sitting inside is reading a book. (i) Is the passenger at rest or in motion with respect to the train? (ii) With respect to a tree outside? (iii) What does this tell us about motion? (iv) Give one more example of an object at rest with respect to one thing and moving with respect to another. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Write the unit with every answer and draw diagrams neatly in pencil.