The Uses of Measuring Tools

1. Measurement of Length- Length is the distance between 2 points

- SI unit for length is metre - in metric system, the units used to measure length are millimeter (mm), centimeter (cm) and kilometer (km). - relationship between units of length 1 cm = 10 mm 1 m = 100 cm 1 km = 1000 m

i. Measurement of straight line ● straight line is measured using metre ruleii. Measurement of curves line ● curves line is measured using string and metre rule.

- When taking a reading, the eye should in the position B so that an accurate reading can be obtained. - If the eye is at the position A or C, the reading taken is not accurate because of an error - This error is known as parallax error.

2. Measurement of Diameter- The diameter of a round object can be measured using a pair of calipers and a ruler.- External diameters are measured using external calipers.

- Internal diameters are measured using internal calipers.

- The thickness of the measuring cylinder can be calculated by the formula: Thickness = external diameter – internal diameter 2 - Example: Calculate the thickness of a measuring cylinder. The external diameter is 48 mm and the internal diameter is 46 mm. Thickness = 48 mm – 46 mm 2 = 1 mm

3. Measurement of area- The area of an object is the surface covered by that object. - The area of irregular shape can be estimated by using graph paper.- Example:

Area = 15 cm2 + 8 cm2 = 23 cm2

* Remember -

4. Measurement of volume- The volume of an object is the amount of space that is occupied by that object.- The volume of liquid can be measured by using measuring cylinder, buret and pipette.

- The correct way to take a reading from a measuring cylinder. 1. The eyes level should be at the position of meniscus level. The wrong position level will cause an error that is known as parallax error. 2. Put a white paper behind the measuring cylinder when taking a reading.

- Remember :-- The eye should be at position B that is at the meniscus level.- The eye at position A and C will cause parallax error.- Put a white paper behind the measuring cylinder.

- The volume of irregular shape solid can be measured by using water displacement method. - Step in water displacement method: 1. Pour water into the measuring cylinder. Record the initial reading. 2. Attach a string to the solid and lower it into the water. Record the final final reading. 3. Volume of the solid can be calculated by following formula: Final reading – initial reading = volume of solid

Example: 40 ml – 30 ml = 10 ml

Final reading

Initial reading