Day 117: Are you kidding? It’s that easy? and The Sledder Lab

Advanced Physics:

Today we summarized the four main energy models; Eelas, Ek, Eg, and Ediss. After this we finally looked at two COE sample problems.  The first one was this:

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It was the same problem I gave the students to introduce the energy unit.  At the time, they solved it (or attempted to) with kinematics and dynamics.  It is about 15 steps to get it done.  I mentioned at the time, we could probably do it in in 2 or 3 steps.  So today was the day to show them that.  They caught on right away… decide your initial and final situations, draw the energy bars so you can write the energy equation, then solve.  For this problem it is Eg (initial) = Ediss (final).  From there I STRONGLY suggested they use substitution… that COE equation boils down to h=μk*Δd.  (There is another step in this, it is to use theΔd and the 70cm rough patch length to find the final resting spot, but that was not thee important part of the lesson.)

In many of the classes I heard comments like the title of the post and that’s actually pretty cool.  One of the reasons I like substitution is that it really helps kids with conceptual questiions like… what happens to the distance is slides if I double the mass?  Well, nothing, mass cancels out.

The second problem was predicting the velocity of a pendulum at the bottom of it’s swing.  This one is equally simple and then we actually check it with a bowling ball pendulum hanging from the ceiling.  We use a Vernier ‘laser-gate’ with one gate timing to check the prediction.  It’s typically very close, but smaller, because there is a tiny bit f energy dissipated.  It provides a chance for us to do this demo:



General Physics:

We discussed the N2L assessment the students took yesterday, then did a fair amount of discussion to get ready for the ‘deployment’ activity.  The assessment was a sledder on a frictionless hill, not realistic at all, because there IS friction.  The goal of the experiment is to determine the coefficient of friction for a sled and the snow.  Yep, we’re going sledding tomorrow.

Through the course of the discussion, we see that we need the angle of the hill,  the combined mass of the sledder and sled, and the acceleration.  To determine the acceleration, we ill be using the LabQuest2 x-accelerometer.  It was absolutely incredible today using the LabQuest Viewer software and our wifi network to show hte students how to set-up and use the LabQuest2.   Way to go Vernier, as always, you guys ROCK.

Day 115: There is NO day 115, but there is a Day 116 and at least the night was awesome

Why is there no Day 115? That would have been yesterday and yesterday every high school in Wisconsin had the same thing going on… state mandated ACT for ALL juniors. Yep, you read it correctly. So, we had no classes, and only the juniors were on campus.  So what about day 116– today, well it was Part 2 of the ACT, the ‘Work Keys’.. that left us with 22 minute classes. Yep, you read it correctly again… 22 minute classes….22 minute classes.  So what made it an awesome night?  Getting to go to another Phox Share Group Share session, hosted by @BrillionNerd.  Besides seeing a great visual on projectile motion from @jcon16, we got to make working electric guitars from @STEMyStuff, so it was an awesome hight.

Advanced Physics;

We had barely enough time to finish the discussion of the gravitational energy experiment.  We concluded that gravitational energy is directly proportional to height.


General Physics:

I felt bad about this… they had a N2L assessment.  We had to do it today so we had time to prepare for the deployment activity.  Here is the assessment question and a hint about the deployment activity on Friday:

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Day 114: I don’t think I did a very good job again…

Advanced Physics:

Unfortunately, not one of the more interesting days in Advanced Physics.  The students were given about 25 minutes to finish gathering data (if needed) and then we had the post lab discussion on the kinetic energy experiment.  We established that there s a square relationship between the kinetic energy and the velocity of the system.  The disappointing thing is that only a few groups (like 3 of 12) had a slope value anywhere near the 1/2m value it should be.  I feel part of this is my fault.  When we did the pre-lab discussion, I thought the students had a pretty good handle on what to do, but after about 2 days of data gathering , seems I was not quite right.  In the simplest sense, the students were to use a spring to launch the cart; get the energy (using COE energy) from the amount the spring was compressed and the spring constant, then plot that against the maximum velocity (from a motion detector).  I know one could do the experiment using a force sensor with the motion detector and calculated columns, but that seems even more abstract.  I think for next time, I will have one station, that I monitor to obtain the spring constants… AND everyone using the Pasco launchers rather than the springs inside the carts.  I’ll also have to remember to make sure the students have leveled the track and used a different mass than other groups, probably a bit more added to the cart to make it more manageable.

In another day or so we will WB the Gravitational experiment…. really not looking forward to it; but maybe I’ll be pleasantly surprised.


General Physics:

Today we worked on three problems involving Newton’s 2nd Law and kinematics (constant acceleration).  Everything is leading up to an assessment and kinesthetic experience… we’re going to ask the kids to determine the coefficient of friction between a sled and snow.  That’s right, we are going to go sledding!



Day 113: Energy Experiments and N2L Practice

Advanced Physics:

This was not really a full day, it was an early release because of Parent Teacher Conferences.  The students continued to gather data for the energy experiment.  The class was split in two, with half doing a kinetic energy experiment, and the other half doing a gravitational experiment.

General Physics:

We had just enough time to work through a sample N2L problem.  We used the WDSS mounted on a cart and a motion detector.  The problem was to determine the velocity of the cart 1.5 seconds after it was released from my hand. The WDSS provided the (net) tension force, so the students had to first determine the acceleration of the cart (verified with the motion detector) with N2L, then the velocity at t = 1.5s (again verified with the motion detector).

Day 112: Energy Labs and Another N2L Kinesthetic Experience

Advanced Physics:

Today we did a pre-lab discussion for the two remaining energy assets, kinetic and gravitational.  The discussion centered around how we could use the knowledge we have of elastic energy to study kinetic and gravitational energy.  It was an easy discussion because most of the students saw pretty quickly that we could use a spring to launch a cart.  To study the kinetic asset, we just need to choose the initial condition (for the energy bar graphs) when the spring has been compressed but the cart is at rest, and the exact instant the spring is no longer compressed (so all the elastic is now kinetic) for the final condition.   For the gravitational, just launch the cart up a ramp, and use the maximum height as the final conditional so all the energy is gravitational.

We have two main springs to use to launch the carts.  The first is the one built into out Pascar’s.  The second is the launcher available from Pasco that looks like this:


Both experiments start with a quick Hooke’s Law experiment to create the Force vs. change in length graph and or (depending on how the group chooses to quantify the energy).  I helped each group use a WDSS Fore sensor and Motion detector at the same time to directly create the ‘Hooke’s Law’ Graph.


General Physics:

Having just discussed N2L, and using the Giant Lab Cart of Physics, we turned to connecting N2L to N1L and N3L.  We accomplished this by using our two giant hovercrafts of physics:



The two examples had the same series of questions… 1. Which person exerted the greater force ? Explain,  2. Which person had the greater acceleration? Explain, and 3. Which person has the greater velocity after the interaction.