Physics Lesson 01 Measuring and Tools

okay so here we are first lesson for real of this video series and this one is just really basic about measurement and what you use for measuring so looking here at these basic implements these are the things that we'll be using often one of these in class during our laboratory procedures so I just wanted to show you really quick I'm sure you're familiar with all of these but this is just a formality so here we go we're gonna zoom in here this is what we call a measuring cylinder we use that for for measuring liquids it's also called a graduated cylinder and it has various markings that tell you how much liquid is in there if you read them properly this is a tape measure right here and then over here we've got a ruler so you're obviously familiar with these a ruler is called in British system sometimes they call it a rule without the R at the end so just in case you ever see that other things that you're looking at here would include stopwatch obviously start stop and reset we'll use those and then this right here is a labquest data logger we won't be using this kind all that often but there is a similar one that we hook up to the computer it is also a data logger so good get to know those a little bit so here we have some sample questions of actual questions that have been on old IGCSE tests you can see here a graduated cylinder and they have a liquid in there and then they have a liquid plus a stone and what are you supposed to figure out the volume of the stone so all you do is you subtract the different readings there you subtract this reading from that reading which you can do by figuring out how much each little increment is and as if you do you can see it's 50 here and it's a hundred there there's five marks so that means each mark must be ten meaning this one here is 75 and then if we look at this one here we have one 100 110 120 125 so 125 125 - 75 so the correct answer should be that one all right and moving along here we have a stopwatch again we've got a situation where you have to subtract the two readings because what it tells you is that this reading was from a previous athlete and then this reading is after this current athlete finishes so what you have to do to find out the time for the current athlete is you take this time and you subtract at that time again you need to kind of zoom in there figure out how many each increment is and you can tell there is 10 5 seconds 5 marks each of these is 1 second however the little marks in between there's only five of them so each of those is point two so you've got ten eleven twelve point four because it's two dots two little hash marks and then if we move over to this one we have 20 21 22 23 and for hatch marks so that's twenty three point eight so what we have there is twenty three point eight and we subtract twelve point four and we do that math we're gonna come out with 11.4 as the correct answer for this problem so the point of this is just to let you see a couple of actual problems that you might have to solve in this sort of a measuring sort of a thing they're pretty easy as you can tell now here we have a different way of measuring things which I want to talk about briefly here is a picture of a pendulum which you've probably seen a pendulum swing it's you know inside a grandfather clock or just any time you have something hanging from a string and it's swinging back and forth that's a pendulum as and then this is a stack of paper which of course all of you are familiar with so as a pendulum swings it goes through its period really rapidly the period is how long it takes for one complete swing from here all the way over and all the way back so in order for that to occur it's it it happens pretty fast actually so what you have here is you want to be able to take it to measure how long that takes if you take your stopwatch and try to start it just as you let go and then let it swing and come back and stop it it's probably a second or less and as you know there's error in how long it takes you to push the buttons so if you just measure one single swing you're gonna have problems there because you're gonna have all of the human error involved so how can you do a better job of figuring out what the actual time is for that and it's pretty simple you let it swing back and forth say ten times so ten swings and then you divide by ten and you can find out the time it takes for one swing and that will tell you the period of a pendulum much more precisely than if you just try to time one single swing same thing with the thickness of a piece of paper if you try to hold a piece of paper up to a ruler you're not gonna be able to measure that right it's just too small now however you could take a stack of say a hundred sheets of paper and then if you have a hundred sheets you can measure that with a ruler divided by say 100 and you will get the size of the thickness of one sheet of paper all right so now I'd like to talk a little bit about some special measuring tools these are designed for measuring very short distances very small thicknesses so this is a second way that you could measure for example the thickness of a piece of paper so you this this first one over here is called vernier calipers so let me zoom in on that vernier calipers it looks like this this part here is movable and if you're measuring outside of something which is usually the case the thing is going to go in between these jaws right here now if you wanted to measure the inside diameter of say like a cup or a graduated cylinder or something like that you could use these teeth up here but will almost never be using these in class if we ever use these tools in class we'll be using this part to measure the outside diameter of things now what's interesting about the vernier calipers is that they can let you measure right down to very small tenths of a centimeter and even smaller than that I believe so here's how it works we're gonna zoom over to this one here so you can see a little bit better what's going on all right so in this picture we're measuring not a hex nut all right so the hex nut is clamped between the jaws there of the vernier calipers and the breeding on the scale is up here above so this is in centimeters all right and you may be thinking to yourself what on earth how do I read this well here's how all right so here we've got your markings for the centimeters one two three and so on and then you've got tens of centimeters in between one two three so each of these lines here is a tenth so this line that says zero lines up next to one of these lines four tenths so basically you can straight away read this as two point and then one two three four or almost to the five but not quite there so we're 2.4 something centimeters all right now here's the tricky part to find out 2.4 what centimeters you have to move over here now as you're going along this line here you'll see that each of these markings on this second scale here this is called the vernier scale each of those markings is offset from the ones above it here so that does not make a straight line you can see here that's offset it's jagged there those don't line up with each other same here all the way down the line none of these markings line up until you get to that one right there this marking lines up very nicely exactly with the markings above it as we continue on this one here's pretty close so you might say that one is it this one you can see already is starting to be offset and this one and then here this is clearly offset from the line above it see how it's jagged there it's not a straight line so you're looking for of all of these numbers here which of them lines up exactly with the hatch mark above it so here jagged jagged jagged jagged line there these lines in here all looked pretty close to the same so it would be a little bit of a toss-up but according to this drawing this is the one that lines up exactly with the hash mark above it so that would be two point four seven so two point four right here plus point O seven there gives two point four seven centimeters and now we're gonna look at a similar device called micrometer screw gauge this this is what it looks like here it's got teeth you put the thing you're measuring in between those teeth this is the barrel that you twist and this is called a clutch which prevents you from damaging the device all right as we look in closer here's a close-up of the scale where you can read it and then we're going to zoom in on that so I can tell you a little bit about how you read this device so here we have the hatch marks that tell you centimeters here we have hatch marks that tell you 1/2 centimeters this barrel is marked with 50 hatch marks each of those hatch marks is 1/100 of a centimeter so basically what you're looking at here is you're gonna twist this barrel around until it's tight against whatever object it is you're measuring so then you're gonna when it's tight you're gonna look at this measurement so what we have here is 0 then 1/2 then 1 then 1 and 1/2 to 2 and 1/2 and so on up to 5 and then 5 and 1/2 so the marking that we can see here is 5 and a half the half mark so we're already at 5 and 1/2 centimeters on this scale so let's write that down whereas a 5.5 all right now what are we going to add to that we're gonna add to that what we see here on the scale so looking at this we want to see which of these hatch marks here lines up with this center line and it's this one so what is that one exactly that one is gonna be 25 26 27 28 so that one is gonna be 28 hundredths so 0.28 so we've got five point five plus 0.28 that's going to equal let's see five point five plus two point eight equals 0.28 rather it's gonna be five point seven eight is what we would say is the reading on that device all right you can go back and watch that again if you want this video is already getting too long so let's wrap it up all right and the last thing we want to talk about is a common mistake that can be made when you're making measurements and taking readings and this is called parallax error parallax so really quick I'll just do this as fast as possible because this video is very long so parallax is what happens when you don't look at your scale straight ahead so basically the bottom line is you need to be doing this you don't want to be doing this you don't want to be doing this and this illustrates how you get the wrong reading if you're not looking straight on if you look at an angle if you're looking from below for example you're gonna read it as this reading as 19.8 to possibly if you're reading straight on you can see that it's 19.7 that's the correct reading if you're looking down and not even you're gonna get 19.6 too so basically your eye is gonna see the wrong thing if you're looking the wrong way all right so you need to be looking straight on that's the bottom line of avoiding parallax error all right so one other quick example let's say you're looking at this thing right here which is something we're gonna be doing actually very similar to this later in the in the class during one of our labs so here again you need to be looking straight at this arrow on this hanging thing here this is a spring a spring with a load on the end and the spring is stretched so the person is trying to figure out how far has it stretched they're using this ruler over here to figure that out now if they don't look straight at that arrow they're gonna end up either measuring too far down or too far up on the scale they're gonna be off by in this case either point to zero point two too high or 0.2 too low so anyway you're gonna measure either too high or too low if you're not looking straight on this is what you want to do not this not this straight on all right great so that's our video about measuring I again a lot of this is pretty obvious some of it should have been new information to you I hope that this was helpful again you can always watch it watch it another time if you need to and see you in class Thanks

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