St. Augustine Preparatory School August 7, 2015 Physics St. Augustine Preparatory School August 7, 2015

Recap Convert the following: 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 1.0303 m h) 1000 kg 2.50 kg i) 6.723 m 0.00032 s j) 4.200 J 3.0x102 mm 45 s 40 s 2.2830 km

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: 24.0 x 1.5 = 36.00/2.00 =

Practice 97.3 + 5.85 = 122.3 – 0.52 = (124.2)(2.1) = (2x102)(1.232) = 24.56 / 2.3213 = 2.02x106 + 1.3x105 = 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 88km/h. What amount of time will it take to travel 705km?

Practice Problems McDonald’s sells approximately 75 hamburgers every second worldwide. How many hamburgers does McDonald’s sell in 3 minutes? In the USA there is an estimated 121 million cars on the road. If the average car travels 16100km in a year and uses 9.00 liters of gasoline every 1.00x102km, 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) 11m + 12.5m + 13m = _____________ 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