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What is the Moment of a Force? - CSEC Physics | Junior Roberts
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- okay all right so we're talking about moments we'll continue with that right now as we say let's just say we have an object like
- this let's just start our door to recap if you have an object like this let's
- say this is a um a plank right and we have that plank resting for example
- on this thing right here right so in other words it's resting on this that is acting as a
- as a what this is keyboard right so we have this acting absorber kind of
- designed to polish a bit so we have this thing right here which is our pivot now when we have this situation right here
- what we're going to see is that let's say we have a force that acts on this plank at the same of a force that acts
- on this plank so in other words it's like somebody comes and sits right here so for example it's like we have a see-saw and we have
- uh someone come and they sit on the seesaw at this point
- right like so so they sit on a seesaw like this so what they're going to do now because they will have a mass
- and they're in a gravitational field they're going to experience a force which is their weight so their weight will now be resting on
- this plank right and produce this force that we direct downward so the weight will be directed downward right because as you know gravity is acting
- downward so we're going to have a force let us say we call that f right so we have this force f right here acting on this object and as we can see
- it is acting at some distance from this point right here which we say is our pivot so because
- this force is acting at whatever distance this is from the pivot what we will see is that this pivot will
- experience what we say is a turning effect or simply put we see that it is a moment so let me just refresh this again
- so again what we're seeing is that we have this object right here right it is resting on this pivot right we have someone who comes and sits
- on this side or sit anywhere could be anywhere once it is at some distance from the pivot
- right in this case the distance d what we're going to see is that this object will experience a turning effect and that turning effect is what we refer
- to as our moment okay yes sir right and we said no that that moment
- which we call which will give the symbol t is simply equal to the product of whatever this force is
- multiplied by this perpendicular distance d okay [Music]
- third ontario information let me know what's going on with you yes sir i'm hearing what you think okay
- good all right so just refresh yourself but it can be much more comfortable in terms of what we cover so this is what we have right here so
- because of this force acting at this perpendicular distance from the line of action of the force so the force is going straight down and the
- distance is taken perpendicularly to the direction of the force so now because of that situation what we see is
- that this object will experience a turning effect and that turning effect is that turning effect will be about this
- particular point okay and we can calculate the turning effect which is the moment by simply multiplying the force and whatever
- perpendicular distance this is okay follow yes sir
- so now let us do a little example let us say we say that this the weight of this person is let us say his weight is 500 newtons
- right and he sitting at a distance let us say 1.6 meters from the pivot right so his weight is 500 newtons and it's sitting
- at a distance of 1.6 meters from the pivot now based on this formula right here we can actually calculate the turning effect that will be produced
- about this point by the weight of this person so now what we do know is we'll just simply
- substitute in our formula and calculate so what we do know we're going to say that the force f is this value so we said 500
- newtons multiplied by the perpendicular distance which is 1.6 meters and this works out to be what
- 800 800 what's the unit now matthew newton no of course
- we're multiplying force in newtons and distance in meters newton meters right so that's how we calculate the moment of
- a force all right okay
- so let's do like two more examples let's do two more examples let's say um i'm gonna make this sort of a worded
- one um let's say um a boy of
- weight i'm gonna keep it simple wait let's say his weight is 520 newton
- sat um let's say 1.5 meters
- from the pivot of a seesaw
- seesaw calculate the moment
- due to the boy's weight boy's weight
- about the pivot
- all right let's see if we can do this uh from the people all right let's see if we can do this
- all right so quickly try this one so we can discuss it okay so this is what we have right the
- seesaw like so and this is the boy sitting right here this is the boy sitting right here like that
- and he's sitting at a distance as you see 1.5 meters from the
- pivot right and his weight is this value which is 520
- newton so now since we want to find the moment or the turning effect about the pivot due to the weight of this person
- we can say that the moment t is equal to is weight which is the force multiplied by the perpendicular distance d
- now what we do from you know as well as plug in the values so we're going to say 520 newtons multiplied by 1.5
- meters when you multiply these out we get 520 times 1.5 is what 700.00 18 80 newton meter
- right so that's all we deal with this one all right now let me give you another one
- i don't want to try you sure yes sir i got the correction i had 1.2 meters instead okay okay okay okay
- all right next one no we're gonna say no um calculate
- the moment due to
- the weight of the girl of the girl in the diagram below
- all right let's see if we can do this thing on diagram below um if she sits
- if she sits let's say uh 1.2 meters from the
- uh from one end from one from
- [Music] one end of a uniform
- let's say this is four meter blank pivoting
- at its center so this one is a little more i've added
- some more information so we have some let me just sketch the alternative you guys see what's going on so we're sorry
- it's like where what's going on we have this thing okay and it is pivoting
- like so all right we got it like that and we have a girl
- this her pink so this girl sitting right here right like that
- right that's the girl and as i said as you see right here she sits um uh what did i say again 1.2 meters so she sits 1.2 meters so
- from where the girl is all the way to here
- is simply 1.2 meters so let's say one point two
- meters and this is a regular the weight of this curl is yes your weight is let's say 480
- newtons all right so let's see what we take on this one
- so again remember when we're calculating moments the distance is always
- the perpendicular distance from the line of action of the force to the wire so you want to answer uh your phone answers it
- yes sir [Music]
- oh and again and again remember that the perpendicular distance
- remember we'll talk about this up right here it's the perpendicular distance from the line of action of the force to the pivot
- right so when we're looking at these questions we have to first determine where is the pivot so this is the pivot right here
- so we need to know what's the perpendicular distance from where the girl sits right where our force will be acting to
- the pivot so we need to determine this distance okay is there any way we can determine the
- distance so we're going to divide um the four meters by eight
- then top shot though one two okay all right so do that and see what happens
- do you 84 newton newtons okay say what you got 384
- actually all right so remember because it is right here that we have a uniform plank
- uniform four meter plant and it is pivoted at the center and because this pivot at the center and it is four meter long then at the center
- will be two meters so from here here is going to be two meters similarly from here there will
- also be two meters now because the coil is sitting 1.2 meters from the end of the plank then the distance from
- where she sits to the pivot which is what we need um for this calculation will have to be 0.8
- meters right so now what we're saying is that the moment t must be equal to whatever force she applies to the planck
- multiplied by a distance from the pivot so now we say this is 480 newtons multiplied by the perpendicular distance which is 0.8
- meters and as we see once we calculate this we get what 384 284 um
- is that okay