g On an Incline

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Students will be able to determine the mathematical relationship between the angle of an incline and the acceleration of a cart rolling down the incline.

Big Idea

How does the value of g change on an incline? Today, we ramp things up with carts rolling down tracks.

Context & Equipment Needs

During the previous lesson students identified how kinematics equations are utilized in the vertical, so our goal today is to apply that knowledge in a lab activity (SP3). Specifically, students will be measuring a cart's speed and acceleration as it moves down a ramp, and then calculating the relationship between the angle of incline and the cart's acceleration (HS-PS2-1). I start the class with a group reading strategy, then we move into the lab activity before doing the fish bowl closure.

This lab will use a the following equipment:  motion sensors, low-friction carts with a ramp, books, meter sticks, a dense ball, and LabQuest interfaces that connect to our MacBook Pro computers. Prior to students arriving, I have a complete set of these materials at each lab station around the room.  

In my classroom we use all Vernier products and so any reference to motion sensors, dynamics carts, etc. implies products manufactured by Vernier.  Pasco has a similar system, but my students are well-versed in using the LabQuest interface that accompanies Vernier products.  They've used Vernier products throughout previous science courses and at other times in this AP Physics 1 course, so my students need little guidance in how to organize and connect the different components.


5 minutes

Taken from Vernier, students introduce themselves to the history of Galileo's Inclined Plane Experiment.   I have this introduction (©Vernier Software & Technology) already projected on a screen at the front of the classroom when students are coming into the room, and I ask 3 different students to read a paragraph.  Since I greet students at my door when they enter, I pick the third, sixth and ninth students who come in to read the first, second, and third paragraph, respectively. It's a fun way to randomize who has the opportunity to read and ensures that I'm not biased in my choices.

As soon as the bell rings, we begin reading. The students who are not reading are expected to be quiet and attentive. After each student reads, I ask a follow-up question to the rest of the class and select a volunteer to answer that question.  After paragraph 1 I ask "Any guesses as to how our experiment today will be different from Galileo's?" My hope is that students look around the room and take note of the materials they've been given and compare those to the first sentence in the paragraph.  Once the second paragraph has been read, I ask "Why is an angle of 90 degrees equivalent to free fall?"  This time I'm hoping students understand that 0 degrees is aligned with the positive x-axis, so a 90 degree angle would be along the positive y-axis.  When the third paragraph is finished being read, I ask students "What do you think is considered a small angle?"  While the answers to this question may vary, I let them know that we call small angles ones that are less than 40 degrees.

Lab Activity

40 minutes

Because I know that my students will not finish the lab in class today, I allow them to choose a partner so that they feel comfortable meeting with the person outside of class.  Also, my students are mature and have a good rapport with each other, so I never have to worry about someone being left out of a pairing.  In the event that someone is absent, I do make an exception for one group of three.  After they have chosen their partners, they need to come to the front of the room to grab a lab (©Vernier Software & Technology) and then go to an already organized lab station.  

Since we already read the first page in our class introduction, I announce to students that they should go right to the "objectives" section on the first page.  They are already familiar with the expectation that they need to check their lab stations with the materials list to have everything needed for the lab.  It is my rule that if something is missing at the end of the class that group is charged with the cost of the missing item.  I find doing this holds kids accountable and ensures my materials don't fall into someone's pocket.  

The students are also aware of my expectation that any "preliminary questions" need to be completed before they start collecting data and included as part of the final, formal lab report. While I won't grade these questions until the lab has officially been submitted, I walk around the room to make sure students aren't skipping over these. Students know that before they can start a lab they must show me the completed pre-lab questions, written on a separate sheet of paper, at which point I skim them and give the students a go-ahead.  Even though this and the materials check are established routines in my classroom, I always remind students about both of these once everyone is at their lab stations. 

The procedure in the lab document is straight-forward, but I still make sure to circulate throughout the room and check-in with the groups.  If time allows and students have the desire, I let them do the included extensions.  When there is approximately 10 minutes prior to the end of class (5 minutes left of the time I've allowed for this activity), I ask students to put everything back the way they found it and return to their seats.  I also tell them at this point when the lab will be due (I usually give them a full week), show them an example of what a finalized lab should look like, and remind them to reference the guidelines for a formal lab report.


5 minutes

Students are back at their desks after cleaning their lab stations, so now I pass around small slips of paper (about the size of a standard sticky note).  Each student should take at least one of these slips of paper so they can participate in our fishbowl closure activity.  I explain to my students that they need to write down one question that they'd like answered about the general concept of free fall or specifically about the lab.  Each student must write something down, fold the slip of paper in half, and place it in the clear bowl at the front of the room.

I keep the room pretty quiet for this closure, as I want students to really reflect on what information they are feeling unsure about.  I also don't want students to all have the same question, which is more likely to happen if students are able to share.  In the past I've noticed that students are sometimes too shy to ask questions, so this activity should give them confidence by being anonymous.  And, I pass around the slips of paper instead of simply handing a student just one so that if they choose, a student can take more than one slip for multiple questions.  

This is a pretty fun activity and I read and answer the questions during the next class period. These are some of the questions I answered during that next class, and they show quite a variety! I use just a stack of blank colored paper and chop it up with a paper cutter in the faculty lounge before class begins.  I also use an actual fish bowl to make the name fit the activity, so that's empty and sitting on my desk at the start of class.  And, to ensure all questions are appropriate and meaningful, I remind students of these requirements and read each slip of paper before going over them!