2. A chain is suspended by a rope as shown at right. The...

2. A chain is suspended by a rope as shown at right. The chain is composed of four identical links and does not move. a. In the spaces below, draw a free-body diagram for each of the four links. Label each of the forces as you were instructed in the tutorial Forces. Free-body diagram for link 1 Free-body diagram for link 2 Free-body diagram for link 3 Free-body diagram for link 4 b. Identify all the Newton's third law (action-reaction) force pairs in your diagrams by placing one or more small "x" symbols through each member of the pair (i.e., mark each member of the first pair as ?, each member of the second pair as ??, etc.). c. Rank the forces on your diagrams according to magnitude, from largest to smallest. Explain your reasoning, including how you used Newton's second and third laws.

Transcript

00:01 So we have this chain link that is suspended like this.

00:08 We have a ceiling and there is a rope and then one chain, two chain, three chain, four chain.

00:19 So one, two, three, four.

00:23 And we want to draw the free body diagrams for all of these links.

00:26 And so we can start with the free body diagram for chain link one.

00:32 So here we have tension, and this is the rope pulling on one, and we have chain link two pulling down on one.

00:50 And i'm going to say that is a normal force of chain link two pulling on one.

00:57 And we also have gravity.

01:04 So we have force of gravity, which will be the same for all the chain links, and this would be the earth pulling on chain link one.

01:16 And we're going to say that all of these chain links have a mass m because they are all identical.

01:24 For two, we have another free body diagram.

01:30 And in this one, we have chain link one.

01:34 We have the normal force of chain link one pulling on two.

01:42 And this was the third law pair with the normal force.

01:46 Of 2 pulling on 1.

01:50 And here we have normal force of 3 pulling on 2, and again we have some weight force where the earth is pulling on 2.

02:05 For chain link 3, we have a normal force where chain link 2 is pulling on 3.

02:15 And so this is another third law pair, which i will denote by 2 dash, just throw it.

02:23 And then we have chain link four pulling on three.

02:30 And again, we have a weight force where the earth is pulling on chain link three.

02:38 For chain link four, we have chain link three, the normal force.

02:48 So chain link three pulling on four.

02:50 And this is our third and final third law pair, and then we have weight force going down like so.

03:03 And so b asks us to identify all of newton's third law pairs, but we've already done that.

03:09 Now we can go to c where we would like to rank forces.

03:13 And we want to explain your reasoning, including how we use newton's second and third laws.

03:18 So we're going to work from four backwards.

03:21 And we've already said that each of these chains has some mass m...

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