APPARATUS • Fulcrum stand and knife-edge • Three clip mass...

APPARATUS • Fulcrum stand and knife-edge • Three clip mass hangers • Meter stick • Laboratory balance • Two unknown masses (approximate values of 180 g and 130 g) • Various masses: two 20-g one 10, 50 & 100-g PROCEDURE A. Exercise 1: Calculate two unknown masses In this exercise, a meter stick will be used as the rotating body. A fulcrum is positioned at the meter stick's center of mass (see Figure 10-3a) and three masses are suspended from the meter stick as shown in Figure 10-3b and Figure 10-3c. Two of these masses, m1 and m3, have unknown values and will be determined in this exercise. We do this by varying the mass of the known mass, m2, and adjusting the position, r3, of the rightmost unknown mass. r1 r2 r3 m1 m2 m3 (unknown) (unknown) Figure 10-4. The experimental set up for Exercise A. Two masses are unknown and will be determined in the exercise. The governing torque equations of this exercise can be written as ?1 + ?2 = ?3 r1F1 + r2F2 = r3F3 r1m1g + r2m2g = r3m3g r1m1 + r2m2 = r3m3 (10.6)

Transcript

00:02 Okay, so i'm not sure exactly what you're looking for on this one because you didn't really give a question.

00:08 You just indicated the apparatus, but i thought i would go through the process so you can kind of see how the equation works.

00:15 So the equation that you have at the bottom when you set up torques, since this would be your pivot point right in here, sorry.

00:24 Put this.

00:25 So this is your beam and your pivot point's going to be right here.

00:32 These mass 1 and mass 2 are going to produce counterclockwise torque and mass 3 would produce clockwise torque.

00:41 So you ended up with what they wrote at the bottom is r1 times mass 1 plus r2 times mass 2 equals r3 times mass 3.

00:52 So the idea is you're going to know r1, r2, and you know what mass 2 is, but you don't know what mass one or mass three is and you're going to adjust this one so it'll kind of work so i'm going to i know some numbers i'm just going to make up some numbers i have them set up and let's just kind of throw this in so i'll start out i'm going to put mass one over here which is unknown but i'm going to put it at 80 centimeters so this is going to be 0 .8 meters away from the fulcrum mass 2 i actually do know i'm going to say i'm going to start off with it being 0 .2 kilograms and i'm going to to put it 0 .4 meters away.

01:33 So i've got two of them and basically i'm putting it half of the distance.

01:37 And then mass three over here i don't know.

01:39 But when i set up everything, i adjust it back and forth.

01:43 And i notice that i have to adjust this and i have to put it at the 0 .4 meter spot to get this to work.

01:52 So this is what i adjust it for.

01:54 So what that does is you would end up with an equation that would kind of look like this.

01:58 It would say that r1 is 0 .8.

02:03 Let's do this in a different color.

02:04 So you've got 0 .8 times mass 1.

02:08 Plus you would know all this part.

02:10 So you'd have 0 .4 times 0 .2.

02:15 And it would equal, and we adjusted it and got the mass 3, which we don't know, has to be at the point 4.

02:23 So in essence, you come up with kind of an equation that looks like this.

02:26 So this is going to be 0 .8 times mass 3.

02:28 That's 1 plus when you multiply those, that's going to be 0 .08.

02:35 And this would be 0 .4 times mass 3.

02:38 So it looks like you can't solve it.

02:40 You're like, huh? i can't solve this.

02:41 I don't have enough information.

02:43 I need more information to actually solve.

02:45 So the idea is you then change mass 2.

02:49 So you're going to put a new one on here...

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