1. WEEEK 3 MEASURING INSTRUMENTS

2. MEASUREMENT OF TIME All day to day activities involve the idea of time. To measure time instruments are needed. In the school laboratory, time is measured with stop watches and stop clock. However, stop watches are more accurate than stop clocks. At home time is measured with instruments called wrist watches, wall clocks, pendulum clock Other uncommon ways of measuring time are use of heart beat, sand clock, ticker timer, etc.

3. MEASUREMENT OF MASS The mass of a body is defined as the quantity of matter it contains. Mass is measured with instruments called lever balance, chemical balance, principle of moment, etc.

4. DIFFERENCES BETWEEN MASS AND WEIGHT Mass is the quantity of matter in a body while weight is the force exerted on a body the earth. The S.I unit for mass is kg while the S.I unit for weight is N or kgm/s 2. Mass is the same from place to place while weight varies from place to place. Mass is a scalar quantity while weight is vector quantity. Mass is measured with lever balance, chemical balance while weight is measured with spring balance

5. MEASUREMENT OF LENGTH Length is called distance. To measure length, instruments like tape rule and meter rule. Cylindrical objects can be measured with calipers and meter rule. Smaller lengths such as the diameter of a rod/ wire, the internal diameter of a tube and the thickness of a plate are measured with vernier calipers.

6. VERNIER CALIPERS It has two scales, the main scale, M and the vernier scale, V. The vernier scale is a small scale which added to the main scale to give the fraction of the smallest division on the main scale. It has reading accuracy of 0.01cm. To take measurement, you check where the zero of M coincides with the zero of V. The vernier scale has 9 division each scale is 0.9mm.

7. MICROMETER SCREW GAUGE It has main scale M and vernier scale, V. It is read by adding the main scale, M and the vernier scale, V. It measures to an accuracy of 0.001cm. The V-scale is divided into 50 scales

8. ASSIGNMENT 3 Draw a label diagrams of vernier caliper and micrometer screw gauge