1Dr. Rachel PepperMy research: physics educationReading quiz.1. The primary physics topic of chapter 3.1 “spring scales” isa.compression of rubber b. gravity and weight, c. physics of springs, d. the outer layer of a fish.2. If the floor in your apartment sags 1 cm with ten people standing onit, how far will it sag with 30 people?a. 1 cm, b. 2.8 cm, c. 1.7 cm, d. 3 cm, e. 6 cm.3. the “spring constant” is a measure ofa. how high you can jump in a given type of basketball shoe.b. the stiffness of a springc. how much water flows out of a fresh water springd. the type of metal used to make a springAnswers: 1c, 2d, 3bCan you drive the car across the bridge without thegiant jumping crocs getting you? Once you get to themiddle in the truck it will be too late if you are wrong.Find max height they jump by throwing food. Predict how far bridge will stretch, without driving on it???a. impossible to predict, just have to try it and hope.b. can tell but have to know bridge materials, your weight and the car.c. need all those plus a good ruler. d. need only ruler, weights of car you. e. can predict if only have ruler and weight of truck. d. can predict if know your weight, car weight, and have ruler.?0meters2-21. go to center of bridge. See that it starts out 2 m above wherecrocs jump to. When you are on it, it sags down to 1.6 m above.2. You weigh 250 pounds, and car weighs 1200 pounds withyou in it.How far down will bridge stretch, and so how far above orbelow the crocs will you be when you drive to center? a. 1.4 m above, b. 0.08 m above, c. 5.68 below! (burp), d. 0.02 me. 1.6 m above. belowd. can predict if know your weight, car weight, and have ruler.?0meters2-21. go to center of bridge. See that it starts out 2 m above wherecrocs jump to. When you are on it, it sags down to 1.6 m above.2. You weigh 250 pounds, and car weighs 1200 pounds withyou in it.How far down will bridge stretch when you drive to center? F = -kx= 250 pounds= k (0.4 m), so k = 250/.4 = 625 lb/m.If 1200 lb = kx, then x = 1200 lb/625 lb/m = 1.92 m. Just make it!!b. 2.0-1.92= 0.08 m aboveNew direction in course, “easier”, more fun.Conservation of energy really useful!! (applications)Can predict what work needed to lift things, what speedthey go if dropped, etc. without ever worrying about details of forces!energy form 1 energy 2energy 3do work to “pump” from one form to another. Amount gained or lost from 1 = amount lost or gained from 2 and 3(also = amount of work done) If know energy change, know work and vice-versa! “physics work”= force x distance2What do we mean by conserved?How do we decide something is conserved?How is this a useful concept?Work with these ideas every day-- money.•You give your friend money – she has more and you have exactly that amount less. There is still the same amount money in the world.•Put money in into bank in one form- quarters,Get out money in other form ($20 bills).oIs there a connection between in and out?oHow do you know what it is?a. Do experiments: find out that if use conversion 80 quarters = one $20 bill, always get predicted number of $20bills out, for number of quarters in. If not, get new bank!Move to islands in south pacific (currency-coconuts tied to dollar). Now putting in dollars to local bank, getting out coconuts?Is bank any good? Number of coconuts out connected with dollars in?a. try converting $50 several times into coconuts, see if number is same.b. try converting $100 dollars and 10$ dollars to coconuts, see if ratio with $50 is x 2 and 1/5?c. convert $20 to coconuts and back see if $20.d. no way to tell except asking natives.e. a. and b. and c. What experiments could you do to check?Why really useful to know that money is conservedgoing in and out of bank? a. can predict how many coconuts will have if put in $20.b. can predict how many dollars will get if start with 15coconuts.c. is of no useAnswer: don’t have to keep track of all the details of what is happening in bank,can know what will get out if put money in in one form and take it out in another.Just have to know the conversion. $1 = 3 coconuts, 100 pennies = 1 dollar,20 1$ bills = 1 $20 bill, …Answer: don’t have to keep track of all the details of what is happening in bank, can know what will get out if put money in in one form and take it out in another.Just have to know the conversion. $1 = 3 coconuts, 100 pennies = 1 dollar,20 1$ bills = 1 $20 bill, …Same ideas with energy.convert between them, find conversion, see that conserved.do bunch of experiments to check.Different forms-gravitational potential = mass x gx heightkinetic = ½ mass x speed x speed,thermal = constant x temperaturespring potential ½ spring const. times (amount stretched)2chemical potential, …Today we’ll look at ramps-How steep a hill can you push a piano on wheels up?How fast will it be moving if it gets lose and rolls down?How much harder must you push to go up shorter, steeper ramp?Is that more or less work?(All connected with concept of conservation of energy.)Demo: Push frictionless cart up 1 meter ramp with “constant” force at constant velocity.h = heightFhandConstant Speed Up If want to push up ramp at constant velocity, force applied by hand must be: a. greater than the weight (=mg) of the carb. less than the weight of the carc. the same as the weight of the car3Demo: Push frictionless cart up 1 meter ramp with “constant” force at constant velocity.h = heightFhandF(gravity + ramp)Constant Speed Up If want to push up ramp at constant velocity, force applied by hand must be: a. greater than the weight (=mg) of the carb. less than the weight of the carc. the same as the weight of the carNeed NET FORCE = F hand-on-car+ F gravity-on-car+ F ramp-on-car= 0 to push up ramp at constant velocityFramp surface Force from ramp is like spring flexing … can only push perpendicular to it’s surface. (for frictionless … if friction, friction acts along ramp.)Fgravity= weight = mg Acts straight down, part of force of gravity is acting along the ramp part is acting perpendicular to the ramp. Amount that acts perpendicular is canceled by Framp surface.FgravityFramp surfaceHow much “work” (force applied x distance) did I have to do to push cart up ramp a distance of 1 meter?pick which one is closesta. 0.1 Joule b. 0.5 Joule c. 1 Joule d. 10 Joule e.