Physics 131, Chapter 1 This class is about classical objects – Bigger than an electron – Smaller than a black hole – Objects you can see/hear/manipulate No quantum mechanics, no string theory No calculus You will need algebra every hour of every day, and trig nearly that often.

Units We will use Scientific International (SI) units The more you use these metric units, the more you will like them. Study the prefixes in Table 1-4. They are taught in grade 7 in Greece. Memorize “centimeter” (cm = m) and “liter” (L = 10 3 cm 3 = m 3 )

Units The period of a simple pendulum is defined as the time necessary for one complete oscillation. The period is given by T = 2  (l/g) 1/2 Where l is the length of the pendulum and g is the acceleration of gravity, in units of length divided by time squared. ? Show that this equation is dimensionally consistent. ?

Cost of Gas in Greece What’s the cost of gas in Greece? Need – Euros per liter – Liters per gallon – Cost of Euros in dollars

Significant Figures Doubtful Digits Given 2 digits, don’t answer with 5! 1. x one sigfig 1.0 x two sigfigs 1 => See national debt. Identify doubtful digits!national debt Odds of perfect NCAA Men’s Basketball bracket: 1 in 9, 223, 372, 036, 854, 775, 808. Identify any doubtful digits. Explain.

Body Mass Index (BMI), Units BMI is defined as wt(kg)/[ht(m)] 2 But we need BMI is units of pounds and inches BMI is defined as A wt(pounds)/[ht(inches)] 2 Find “A” BMI OK 30 UK “keep your waist circumference to less than half your height.”

Is your answer reasonable? Given: 250 x 10 6 packages of French Fries ? End to end, how long? Estimations can be valuable in deciding if your answer is “in the ballpark.”

Sigfigs – block of gold Gold bar L = 5.62 cm W = 6.35 cm H = 2.78 cm Don’t throw away any digits until the end. Let your calculator do the work. Do the whole calculation as one operation.

Too many sigfigs? Ear thermometer Precise to 0.1 o F Accurate to 0.5 o F

Scalars and Vectors A scalar has a numerical value A vector has both a numerical value and a direction. Think of an arrow. We’ll use “speed” as a scalar and “velocity” as a vector for this course.

Chapter 2 Motion in one dimension – straight line Distance – a scalar, has magnitude Displacement – a vector – From its beginning to its end – Has a magnitude – Has a direction – Expressed as a vector a

Velocity Average speed – total distance / total time. Average velocity – average speed in a direction

Average velocity example Home to top of hill = 10.0 km Pedaled up at average sped of 5.00 km/hr. Q1. average speed? Q2. average velocity? Q3. what speed down to average 10.0 km/hr for the trip ?

Cross Country Car Race Two cars travel in the same direction along a straight highway, one at a constant speed of 55 km/hr and the other at 70 km/hr. (a) Assuming that they start at the same point, how much sooner does the faster car arrive at a destination 10 km away? (b) How far must the faster car travel before it has a 15-minute lead on the slower car?

Average Acceleration A car traveling in a straight line has a velocity of +5.0 m/s at some instant. After 4.0 s, its velocity is +8.0 m/s. What is the car’s average acceleration during the 4.0-s time interval?

Section 2.5 Constant Acceleration !!! We only deal with constant acceleration in this course. !!! 2-7 v = v o + at 2-8 x = x o + v av t 2-9 v av = ½ (v o + v) 2-10 x = x o + ½ (v o + v) t 2-11 x = x o + v o t + ½ a t v 2 = v o 2 + 2a (x – x o ) = v o 2 + 2a (  x)

Drag Racer Assume: constant acceleration Goes quarter-mile (402.3 m) in 5.0 seconds What average acceleration?

Steam Catapult on Aircraft Carrier Given: 175 mi/hr ( m/s) in 2.5 s a)Find average acceleration b)Find distance traveled on deck

Parachute Assume: before parachute opens, descending at -5 m/s Assume: after parachute opens, descending at -1 m/s Assume  t = 1 s ? Acceleration during that exciting second

Superball Given: 50.0 g superball Given: thrown toward brick wall at 25.0 m/s Given rebounds at 22.0 m/s from the wall Ball in contact with wall for 3.50 ms ? Average acceleration ?

Lab 1 Learn to use the motion sensor Learn to use the Smart Tool Learn to use the Slope Tool Lab 1 is designed as your “how to” lab Bookbags under tables, not in walkways! May start at 1:00 p.m., must start by 1:15 p.m.

Lab 1 info The act of “printing” creates the pdf file on the computer “desktop” which you will to the instructor. I mark you “present” for a lab when I get your pdf file. Check with me as you leave the lab to be sure you sent it and I received it!