Physics St Augustine Preparatory School August 7 2015

Physics St. Augustine Preparatory School August 7, 2015

Recap • Convert the following: 1) 2) 3) 4) 1125 meters in kilometers 114 centimeters in meters 525. 3 grams in kilograms 10. 23 kilograms in grams

Significant Figures • Significant figures (also called significant digits) are important as they indicate the precision of a measurement • Page 18 in your textbook has the rules for determining the amount of significant figures in a number

Practice a) b) c) d) e) f) g) 1. 0303 m 2. 50 kg 0. 00032 s 3. 0 x 102 mm 45 s 40 s 2. 2830 km h) 1000 kg i) 6. 723 m j) 4. 200 J

Rules for addition and subtraction • When adding and subtracting numbers, the final answer will have the same number of decimal places as the number used in the addition/subtraction that had the least number of decimal places. • Examples: 121. 03 + 5. 8 = 125 – 5. 5 =

Rules for multiplication and division • When multiplying and dividing, the final answer must have the same number of significant figures as the number used that had the least number of significant digits. Examples: a) 24. 0 x 1. 5 = b) 36. 00/2. 00 =

Practice 1) 2) 3) 4) 5) 6) 7) 8) 97. 3 + 5. 85 = 122. 3 – 0. 52 = (124. 2)(2. 1) = (2 x 102)(1. 232) = 24. 56 / 2. 3213 = 2. 02 x 106 + 1. 3 x 105 = 1. 000 + 2. 01 + 3. 523 + 2. 6 = (1. 20)(2. 212)(0. 0035) =

Why have we done all this? • Physics involves the use of a lot of different equations to describe relationships. • For example: – Velocity = (distance)(time) – Force = (mass)(acceleration)

Using units to solve problems • Even without knowing a formula, you can solve many physics problems just by looking at units Ex. A car is travelling at a constant velocity of 88 km/h. What amount of time will it take to travel 705 km?

Practice Problems • Mc. Donald’s sells approximately 75 hamburgers every second worldwide. How many hamburgers does Mc. Donald’s sell in 3 minutes? • In the USA there is an estimated 121 million cars on the road. If the average car travels 16100 km in a year and uses 9. 00 liters of gasoline every 1. 00 x 102 km, what quantity of gasoline is used annually in the USA.

Units for Answers • The units (and significant figures) that we use for our answer must stay consistent with what was used to find the answer. Ex. 1) 11 m + 12. 5 m + 13 m = _______ Ex 2) 13. 2 m / 1. 3 s = ______ Ex 3) (13. 3 s)(2. 0 s) = _______ Ex 4) 1. 5 s / 0. 50 s = ______

Accuracy and Precision • Accuracy: How close to the actual value a measurement is • Precision: How close together two or more measurements are to each other. • You can be precise, without being accurate!

Consider the game of darts, if a person is aiming at the center of the board.

Chapter Review Questions Page 28: 13 – 16, 18, 20, 21, Page 30: 37, 38, 44