Simple Machines (1 of 7) Pulleys; Defining Forces, Distances and MA, Part 1
okay in today's video I am going to go over the following terms for
machinesand how they relate directly to
pulleysone of the most common kinds of
machinesespecially if you're in school okay we have the input force the input distance the output force the upward distance and the mechanical advantage those are the five terms as I say for those are the five terms we're going to go over alright and this is how it works this is the pulley machine these are the
pulleysthis is a
simplemachine we have one pulley two police three
pulleyswe're usually when we have them group together we think of this it's like the top pulley the two and then this bottom pulley this is the string we would pull and this is the object it starts here we're going to raise it up to here okay so the first thing and maybe that's the most straightforward thing is the output force is the weight of the object that we're trying to lift its measured in Newtons if you measure your weight in the metric system you measure it in Newtons and the weight of the object you mean the weight of the object is the output force that's the force you're trying to get out of the machine you want to raise that thing up that's the force you're trying to get out and usually we draw that we draw a pointing straight down because the force points down the output force and it's equal to the weight so if somebody was to say in a problem oh we were...
trying to lift an object with a weight of 20 Newtons that's the output force in this case okay then we have the input force that's the force you put in to the machine that's why they call it the input force and it's usually just the force you apply to the string when you pull the string you have one of those spring scales you attach it to the end and you pull and that's the input force that's the force you put in this is the force you're trying to get out this is the force you put into the machine it's also measured in Newtons okay then we have the output distance OD that's the distance that's the object is ready that's what you're trying to get out of the machine you're trying to raise it some distance that's what you want to get out that's why it's called the output distance it's the distance that the object moves up because in this case you want to move this thing up so we go from here to here that is the output distance then we have the input distance okay the input distance is the distance that you actually move the string when you pull the string you pull it up in this case and you pull it that far the distance that you pulled that's the distance you put in that's the input distance okay and that would be met and the
distancesit should be measured in meters sometimes you measure in centimeters but really they should be measuring the base unit for the metric system which is the meter all right...
so those are the four terms output force of' input force i F that's what you measure with the scale the spring scale the output distance is the OD that's the distance the object is raised and the input distance is how far you pull the string okay you should be familiar with those four terms and how they relate to police okay now let's just go over what the mechanical advantage is all right the mechanical advantage knot has kind of a technical definition or a technical sounding definition but I think the best one I found is it's the factor by which the
simplemachine multiplies the input force and really with
machineswe want to be able to put more force in excuse me less force in and get more force out that's why we use a
simplemachine if we want to be able to raise something up that's a hundred Newtons we don't want to have to use 100 Newton's of force okay and we'll go over some problem and figure that out but it's the force it's the factor by which the
simplemachine multiplies the input force to give us the output force all right now there's two equations the mechanical advantage MA can be found by taking the output force and dividing it by the input force or you can take the mechanical advantage equals the input distance divided by the output distance the mechanical advantage is a unitless number because the
distanceswill cancel okay now for
pulleysand only for
pulleysbecause that's the only...
one that really has a string you can determine the mechanical advantage by counting the number of strings supporting the output force or supporting the weight okay so all we do is we count the number strings and this is what I mean by that we have our pulley system over here we're going to oh yeah but we want to figure what the MA is we're going to figure out what the MA is we just count the number string the way we do that we just looked across the middle between the two
pulleyshow many strings are supporting because really this string supports the weight this string supports the weight this string supports the weight and this string supports the weight so you just look across you count and you come up in this case the mechanical advantage of this pulley system is four so this pulley system is going to multiply the input force by four so for example if we put 20 Newtons on the scale we pull the string the input force with 20 Newtons we're going to be able to lift an object it has a weight of 80 Newtons we're going to multiply the input force by a factor of four just count the number of strings okay so that's a quick video goes over those four terms output input input output
forcesand mechanical advantage in the next video we'll actually do some calculations where we calculate some of the
distancesokay thank you very much for watching I hope you found it helpful if you found it helpful you can give me a thumbs up or...
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