hello everyone in this video we are going to cover chapter 3 section 3 temperature so this section is all about being able to convert between different temperature units so um temperature in degrees fahrenheit degrees celsius and also in degrees kelvin so in our everyday lives we tend to work with degrees fahrenheit right we get our temperature from the weather channel or we take our um our body temperature but um in the in lab uh we tend to work in celsius uh and also in kelvin which is the si unit for temperature so that's that system international for units so before we get into these couple of examples i'm just going to write down the equations for converting between these different temperature units so if we have a temperature in degrees fahrenheit and we want to then find out what the temperature excuse me if we have a temperature in degrees of celsius and we want to solve for that temperature in fahrenheit then we take degrees celsius and we are going to multiply that by nine fifths or 1.8 and then from that we have to add 32 now if we just want to rearrange this equation to then solve for temperature in celsius we would say degrees fahrenheit minus 32 just rearranging the equation that would have to be in parentheses and then we would multiply this by 5 over 9. degrees celsius now if we want to convert from degrees celsius to degrees kelvin it is a much more straightforward calculation to perform so to get a temperature in degrees kelvin we take that temperature in degrees celsius and we add to it 273 and the reason that we use kelvin uh just for a little bit of background is because kelvin has what is considered an absolute zero um so it is very useful um in in lab and in scientific applications in general so now that we have these uh written out let's go ahead and um and and do these example problems so for 3.18 calculate the unknown temperature in each of the following so if we had 25 degrees celsius that's right around room temperature so we would use first this version of the equation since we have degrees celsius and we want to solve for degrees fahrenheit and we would say 25 times 9 over 5 plus 32 and we just put that into our handy dandy calculator 25 times that 1.8 or nine-fifths we get 77 degrees fahrenheit uh which my husband would argue is too hot for room temperature okay now if we have a temperature in degrees fahrenheit and we want to express that as degrees celsius now we need to use this equation so that is 65.3 minus 32 [Music] times 5 9. plug that into our handy dandy calculator and i get 18.5 degrees celsius so um just kind of you know one observation that we can make by looking at these calculations is that when we are converting a temperature in degrees fahrenheit 2 degrees celsius that temperature in degrees celsius should be lower than it is than what it is when it is expressed as degrees fahrenheit and then if we wanted to take uh this just one step further to then take our temperature in degrees celsius and figure out what that would be in kelvin degrees kelvin we would just take our calculated temperature eighteen point five plus two seventy three and so i would also say i know that this textbook uses just 27d3 but it really is known more precisely it's 273.15 just based on the rules for sig figs when it comes to addition and subtraction that .15 often doesn't make very much of a difference but just kind of a more you know we do know that value more precisely and so we would then report this number as 2 90 one okay degrees kelvin hello everyone uh in this video i'm going to cover the information in chapter 3 section 4 where we talk about energy so we um going through some examples to distinguish potential energy from kinetic energy so kinetic energy is energy uh imparted by by motion okay actual movement um whereas potential energy is energy based on uh position or also potential energy can be stored in chemical bonds that upon reaction can be released and then i will also take a look at some units that we use to describe energy values so for 3.24 indicate whether each of the following statements describes potential or kinetic energy so for a we have the energy in your food so this would be an example of potential energy so certainly if we uh consume the food it is digested we have the breaking of chemical bonds and the release of energy that that is stored energy in the food that could be released if we consume the food so this would be potential energy for b we have a tightly wound spring and so through the act of tightly winding the string the excuse me the spring we are storing energy there that could then be released but uh in the beginning it is just potential energy so no no movement happening there if it's just already tightly wound so again potential energy for c we have a car speeding down the freeway so this is an example of kinetic energy the car is in motion if that car comes into contact with something else it could impart that energy to that other well i don't really like this example that other structure that other car but this is energy due to movement so kinetic and then lastly we have an earthquake so the actual you know ground shaking i know that earthquakes is not something that we deal with in louisiana um but i'm sure many of us are you know familiar uh with visuals of earthquakes through news or other media and we know that based on that shaking of the earth right the walls shake and it causes um uh it it transfers energy to to other structures and things so this would be another example of kinetic energy okay so that's the the big difference between potential and kinetic okay do we have um you know energy you know kind of uh um stored to potentially be used later um or do we have energy through actual motion um so for 3.28 here's where we take a look at some units associated with quantities of energy so in 3.28 a person uses 750 kilocals on a long walk calculate the energy used for the walk in each of the following energy units so we have joules and kilojoules so we do need one conversion factor in order to convert from kilocals to joules actually two conversion factors um the first one is that there are 4.184 joules per uh calorie or cow and then the other conversion factor just has to do with the multiplicative prefixes so if this is a kilo calories we know that there are 1 000 calories per [Music] kilocalorie um and the same would be true for joules and kilojoules where there would be 1 000 joules per kilojoule so again just our multiplicative prefixes so our known beginning is the 750 kilocals so we'll write that down and we are first trying to get to joules but before we can use our conversion factor as we have written we're going to need to convert from kilocals to cals calories and we know we need to cancel out kilocal so one kilocal is 1000 calories and then from there we can use our other conversion factor to get from calories to joules and so the calories uh need to be cancelled out so they must go in the denominator of our next factor so 1 calorie 4.184 joules calorie and calorie cancels out so two significant figures um this is uh these are exact numbers and then uh we have four uh significant figures here so we're going to be limited to two significant figures in our final answer so if we have 750 times 4.184 and then we divide or excuse me and then we multiply that by one thousand and i get first this number three million 138 000 but as we mentioned we can only report this to two significant figures so we would write this as three million one hundred thousand joules okay and so now uh to express this in kilojoules now we just need to take this value and we are going to say that there are 1000 joules per 1 kilojoule or 10 to the third and so i'm going to rewrite this in scientific notation and so that's one two three four five and six and that would be one kilojoule over [Music] 10 to the third joules so then our final answer in kilojoules would be 3.1 times 10 to the power of 3 right because our digit term would remain unchanged but we would look to our exponent term 10 to the 6th and then we would have to subtract the three okay um so there you go that's just a little bit of practice for converting between different energy units and also distinguishing between potential and kinetic energy