1. CHAPTER 3 Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII

2. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII MEASUREMENT  DEFINITION Measurement is a process of comparing one quantity which is measured by the quantity of the same sign and is determined as unit  The length measuring instrument and its precision A. RULER The smallest scale of ruler is 1 mm (0,1 cm), and its precision is the half of its smallest scale; 0, 5 mm (0,05 cm)

3. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII MEASURING INSTRUMENT FOR LENGTH B. SLIDE-GAUGE Slide-gauge’s precision is 0,1 mm, it means the accuracy of this instrument comes to 0,1 mm Slide-gauge has two kinds of scale : - Main scale, its unit is cm - Nonius scale, its unit is mm

4. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII MEASURING INSTRUMENT FOR LENGTH

5. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII MEASURING INSTRUMENT FOR LENGTH C. SCREW-MICROMETER Main scale, consisting of scale of 1mm,2mm,3mm, so on, and the Middle scale, consisting of 1,5 mm, 2,5 mm, 3,5 mm, so on. Rotating-scale, consisting of 1 to 50. If the rotating scale steps 1 to back, the main scale will move forward 0,5 mm 1 rotating scale = 0,01 mm

6. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII SCREW-MICROMETER Scale Reading figure1 1.Watch out the rotating-scale, where it is in the main scale. The main scale length of the selected object is 2 mm. 2. Watch out the pointing on the rotating- scale. 43 on rotating scale is closely pointed with the horizontal line on the main scale. Then, the reading of the micrometer = 2 + (43x0,01) = 2 + 0,43 So, the length of the object is 2,43 mm

7. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII SCREW-MICROMETER Scale Reading figure2 1. Observe the rotating-scale, where it is on the main scale. The main scale length of the selected object is 4,5 mm. 2. Observe the pointing of the rotating- scale. 39, on the rotating-scale is closely pointed with the horizontal line on the main scale. Then, the reading of the micrometer = 4,5 + (39x0,01) = 4,5 + 0,39 So, the length of the object is 4,89 mm

8. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII THE MEASUREMENT  The measuring instrument of Mass Arm Balance In our daily life, the mass of object is stated in various units, such as gram (g), milligram (mg), ons, ton (t) and quintal (kw) 1 ton = 10 quintal = 1.000 kg 1 kg = 1.000 g = 10 ons

9. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII THE MEASUREMENT The measuring instrument of time Stopwatch Hand-watch

10. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII INDETERMINANCY IN MEASURING Some things to be considered in measuring Accuracyprecision To show the accuracy level of a measurement To show how accurate the result of the measurement compared with the real object

11. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII PRECISION AND ACCURACY The ruler generally has the smallest scale of 1 mm, while the slide-gauge comes to 0,1 mm. the measurement using slide-gauge will be more accurate than using ruler.

12. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII THE SAFETY IN MEASURING The mishap in laboratory could occur because of some causes, for instance : 1)Not obeying the rules in laboratory, 2)Not having good attitude in doing the laboratorial activities, 3)The lack of comprehension and knowledge on the instruments, objects, and the procedures of usage, 4)The lack of explanation from teacher or laboratory assistant, and 5)Not using the safety lock.

13. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII THE SAFETY IN MEASURING There are some risks that should be anticipated in the laboratory area as follows : 1.A wound because of fire, 2.Electric threatening 3.Radioactive danger, and 4.Fire risk.

14. Electindo.com PHYSICS FOR JUNIOR HIGH SCHOOL VII THANK YOU