We briefly discussed the answers to the Ranking Task I handed out yesterday. Here it is:Unit 6 Ranking Task-The Merry Go Round –All Questions
Most of the students did very well on it. In regards to the last question, I asked a series of questions aimed at gauging if the students understood a key concept about uniform circular motion and radial force. Here it is:
Me: What is acting as the radial force in this example.
Ss: The static frictional force.
Me: Good, which rider, D or F has a greater static fictional force?
Ss: They have the same static frictional force because they have the same mass and the we an assume he same coefficient of friction.
Me: Good. I see you have Rider D with a greater radial force than Rider C. Why is that?
SS: Ummm…. well….. let’s see…..
OK, it was not really like that for the last response, but it did take a bit of time for the classes recall that there is a difference between a required radial force and whether or not the force supplying it is larger enough. I used an analogy. Let’s say I go to Starbucks and I want a coffee that costs $3. I have some dollars in my pocket, but just because I have some dollars that does not necessarily mean that I have enough dollars. I have to actually check to see if I have enough. If I have $4, I’m good to go, but if I have only $2, I don’t have enough and I get no coffee.
They students worked on 7 problems in class in small groups. No group finished all 7, so (by design) they will have some to work independently on. I suggested which ones were more challenging that they should work with their partners on. This type of approach (in class time to work) is a bit new to me, I usually do not allow extended periods of time for this. I don’t think it is a bad thing, I just want my students to realize they will have to do some independent work too.
Today was about throwing numbers into the net fore equations we have been writing as we draw force diagrams. I gave them a series of situations, they solved for the tension force, then we checked it:
Even though it is hard to read, the last problem set the students up to do a static equilibrium challenge tomorrow. Here is a better picture of the last problem:
They were given one of the tension forces (measured by the WDSS) and an angle. Tomorrows problem is very similar, but with both strings angled.