Tools of Physics

1. Tools of Physics Accuracy Precision Sig Figs Graphing

2. Ruler (metric)(Overview) • Used to measure length/distance • Units of measure: centimeters (cm), millimeters (mm) • Markings • Each small (unnumbered) line is a millimeter division • Each long line followed by a number is a centimeter division • 10 millimeters in a centimeter 1 mm 1 cm Important – this is only a portion of a ruler

3. Meter Stick(Overview) • Used to measure length/distance • Units of measure: meter (m), centimeter (cm), millimeter (mm) • Markings • Each small (unnumbered) line is a millimeter division • Each long line followed by a number is a centimeter division • 10 millimeters in a centimeter • 100 centimeters in a meter How many millimeters are in a meter? 1 mm 1 cm Important – this is only a portion of a meter stick

4. Stopwatch(Overview) • Used to measure time • Units of measure: seconds (s), minutes (min) • Buttons • Split/Reset: • Mode: • Start/Stop

5. Significant Figures (Sig Figs) What are significant figures? They’re sort of the "interesting" or "important" digits of a number. They indicate the precision of a measurement Rules: • All nonzero numbers are significant (8762) • Leading zeros are never significant (0.035) • Imbedded zeros are always significant (2005) • Trailing zeros are significant only if the decimal point is specified (400 vs. 400.)

6. Precision vs. Accuracy • Accuracy: the closeness of a measured value to a standard or known value. • For example, if in lab you obtain a weight measurement of 3.2 kg for a given substance, but the actual or known weight is 10 kg, then your measurement is not accurate. • In this case, your measurement is not close to the known value and therefore, not accurate

7. Precision vs. Accuracy • Precision: the closeness of two or more measurements to each other • If you weigh a given substance five times, and get 3.2 kg each time, then your measurement is very precise. • Precision is independent of accuracy. • You can be very precise but inaccurate. You can also be accurate but imprecise.

8. Precision vs. Accuracy

10. Recording Measurements • When recording a measurement, include all of the known digits plus a final estimated digit.   • For example, in the ruler below it is marked every one centimeter so we know the ones place and could record 2. • But we must also estimate one, and only one, additional digit.   • So in this case we might record 2.3 cm or perhaps 2.4 cm. • Either would be correct as the 2 (ones place) is precisely known while the final digit (tenths place) is estimated.

11. Recording Measurements • When recording a measurement, include all of the known digits plus a final estimated digit.   • Now consider the next ruler.  In this case, the ruler is marked in both ones and tenths meaning that we can clearly see the first part of the measurement is 2.3. However, we must again estimate one additional digit or place – 2.35 cm.

12. Graphing Distance vs. Time • Time will be on the x-axis because it is the independent variable • Distance will be on the y-axis because it is the dependent variable (the distance traveled depends on the amount of time)

13. Graphing Distance vs. Time ° ° °