A Video on “Importance” in the “Explicit Direct Instruction” …
Over the past two weeks I’ve been doing a lot of new things, and I want to get them down:
#1 Hover pucks
Not only using hover pucks, but revisiting them again and again. We began forces by taking hover pucks out into the hallway and observing, describing in words, and drawing velocity vs. time graphs for
We visited the pucks again before vectors and projectile motion. We sent them going down one hallway, and when they got to the second hallway, we tapped them in the other direction. Students made predictions and observations, once again using words, but this with pictures showing the trajectory,
We visited hover pucks again when making a bridge from projectile motion to circular motion. How to get the hover puck to move in a circle by tapping?
Beyond just “using” hover pucks”, hover pucks became an anchoring context for conversation again and again. Oh, I almost forgot, before the first time we used hover pucks, students took one of the formative assessment activities from Paige Keeley’s book, “Uncovering student ideas in physical science.” It was the one where there is a list of a dozen or so statement about force and motion that students have to agree or disagree to. I had students commit to answers before, and then revisit after. As a class, we talked about a few sticky ones.
#2 Velocity vs. Time Graphs
This summer, velocity vs. time graphs are the major tool we use all the time. As others have said, velocity vs. time graphs are rich with information. The great thing about velocity vs. time graphs is that you never stop using them.
I think that the first activity with the hover pucks was only successful because we had spent a lot of time the week before working with velocity vs. time graphs. Students worked problems using them. My exams required students to interpret them and draw them. I asked clicker questions using them, both before and after hover pucks, and all the time. Questions included quantitative ones, qualitative ones, and questions that went back and forth between considering position vs time and velocity vs. time.
One last note about velocity vs. time graphs. This summer, on any problem involving forces, I have not once given students acceleration or asked them to solve for it. If they need acceleration, they need to get it from a velocity vs. time graph or from a table with data. If I am asking a question about motion, it is about how much the object’s speed will change in a given time, or how much time it will take to go from one speed to another.
#3 Positioning Students as Authors of Ideas and Equations
To a degree, I have always done this. The first semester I taught here, a student named Ashley proposed the tentative idea that when you throw a ball up with a certain speed, it will hit your hand with the same speed. That idea became known as Ashley’s idea, which students used throughout the year to solve problems via symmetry. This year, a student proposed the idea that finding the velocity of an object is the same as finding the slope on a position vs. time graph. That rule is known in our class as Chelsea’s Rule. We also have a Yalda’s rule. etc.
What I am doing differently this year is framing Newton’s 2nd law as an activity of inventing equations. See in kinematics, the equations are pretty much always the same, but with forces, the variety of equations you can write increases a lot. AND, a single equation can describe different situations.
Typically, when we are working on force problems, my instructions are:
In the past, students have had a really hard time when we start writing lots of equations without any numbers. While it is still hard and intimidating, it is much easier this year than before. I think some of this is because I am positioning students as inventors of those equations; rather than their being a right equation that was known ahead of time, which they were merely supposed to recreate.
Tied with this, we have been doing lots of Alan Van Heuvelen’s Jeopardy questions. I’ll write an equation like this on the board
T – (150 kg) (10 N/ kg) = (150kg) (-2 m/s/s)
and students will have to draw the free-body diagram and describe the situation. While there is only one free-body diagram really, there are multiple situations, because the -2 m/s/s doesn’t tell us direction its traveling or whether it’s slowing down or speeding up, so there’s a rich conversation to be had.
I think the Jeopardy questions pair well with the idea of inventing equations that describe situation, and positioning students as authors of equations. Another big thing to note is that forces isn’t the first time we did Jeopardy equations. I introduced them during kinematics as equal, and we practiced them with projectile motion. I even have exams questions with them.
#4 Leveraging History of Physics and Contemporary Physics
This paper by David Brookes and Eugenia Etkina has changed the way I think about thinking about force, learning force, and teaching force. It’s changed my thinking in a lot of ways, but one influence it has had is in helping me talk about students’ difficulties learning through the lens of history. This may sound crazy, but I explicitly talk with students about the words force impressa and force viva. I talk about this on the very first day after we’ve done the formative assessment and hover puck activity, and students are revisiting their initial ideas.
In talking about current days physics, I am doing a better job of framing the work we are doing in terms of current research. This is a perhaps a contrived example, but I think it still helps. We do this lab–one that I don’t like all that much–where students use uniform circular motion data to determine the mass of a ball. I frame this lab as involving the same set of ideas that astronomers use to study dark matter and in finding planets. (OK, it’s not exactly the same, but close). We talk just a little about how we measured the period of the ball going around, and how Astronomers measure the period of planet going around a star very far away. I didn’t make a whole lecture of it, and I wasn’t trying to sell the lab as something cool. It’s just a little thing that helps put our class in contact with larger participation in physics.
I also explicitly talk about the history of physics with Galileo. I spent the early part of the summer reading all of Galileo’s Two new Sciences. We talked about Galileo’s definition of uniform motion and why he changed it. We examine data and try to make sense of what Galileo meant when he said falling objects follow the odd number sequence. The more I know about the history, the better I find myself able to teach that physics.
#5 Working “problems” with data gathered in class, rather than contrived made-up stuff
Instead of working on some circular motion problem that I thought up, we get a buggy going in a circle with a string. We try to figure out how much tension is in the rope, and students help decide what data to take and help take data. I even have more than one students do the timing and the distance measurement, so we can do uncertainties if we want. I’m doing a good job of doing this quickly, and not dragging it out and making it a lab. It’s just a problem. Sometimes, we’ll try to verify our answer by taking more data; but I don’t have to if we are pressed for time.
#6 At-home experiments and in-class everyday object labs
I’ve had students share experiments with family and friends (dropping paper and book). I’ve had students make predictions and make observations (running key drop) at home. I’ve had students grab everyday objects and share observations and thoughts online (one where students had to get two pairs of shoes and describe what they notice about each that’s informing their decision about which has better traction). In class, students brought their shoes, and we did a lab to calculate the coefficient of friction between shoes and the floor.. I think I got this from Frank Noschese, but can’t find a link.
I have a goal, which is to help break down the walls between my class and the rest of their lives. I do this by asking them to share their learning with others, and to bring those others’ ideas back to class. I ask students to bring stuff to class into do experiments on. I ask them to do experiments at home. Maybe, just maybe, it will make a small dent.
#7 Bridging Analogies:
This year I did two of the bridging analogies described in this paper by John Clement. We did the Normal Force one and the Friction one. Because of time, one of these was done more teacher-centered than I would have liked.
#8 PhET Simulations
Right now, I am mostly PhET simulations using these for “lecturing”. I used moving man to introduce the number line as the system we are adopting for describing linear motion. I also used the vectors simulation for formalizing our observations in the hallway (with tapping hover puck in orthogonal directions).
I imagine I could get students more involved in the future, but for right now this is how I am making use of the simulations.
#9 Online Videos from Veritasium
There are multiple reasons for this, but one is to supplement our text, but another is to learn through refutation text (or video).
#10 Mindset Conversations
So far this year, we have talked a lot about learning how to learn. I have been most encouraged by John Burk to make this an important part of my class. A comment here describe a bit of what I have done so far.
Oh, and of course, my last post, about interaction diagrams.
** When I read all of this, I have think to myself, “How in the world did we do all of this happen in two weeks?” I have no idea…
Oh, right, and don’t forget about standards-based grading!
I’ve been teaching using schema system diagrams, which I have just been calling interaction diagrams in my physics class. It’s the first time I’ve ever taught using them. I’m sold on them after one week.
Here is the biggest reason why I’m sold.
The diagrams provide a productive outlet for really good student ideas, which previously would have been considered misconceptions. An example:
Today, we started doing circular motion. We had a constant velocity buggy going around in a circle by means of a string. Just before we took some data for the time to get around and the radius of the circle, students were drawing interactions diagrams and free-body diagrams for the situation.
Three of eight groups included me in the interaction diagram, interacting with the string and the string interacting with the buggy. It’s a wonderful idea to think about that the motion we are observing hinges on the fact that I have pinned down the other end of the string. It’s insightful and correct—with out that interaction, there would be not constraint to move in a circle. Now here’s the important thing: Previously, with out interaction diagrams to provide a place for that idea to go, that idea would have made its way to the free-body diagram. You could think that the reason I like the diagrams is because they prevented a mistake, but I really like the diagram because they provide a productive placeholder for valuable insights and ideas.
Three other groups included the motor in their interaction diagram. Each of those groups placed the bubble of the motor inside the bubble of the buggy. The really wonderful idea here is that none of the motion we are observing would not be happening without the motor. The buggy would screech to a halt. Previously,when teaching without the interaction diagrams, that wonderful idea would not have had a productive outlet, so many students would have included a motor force on the free-body diagram.
So sure, one cool thing is that no group got the free-body diagram wrong. One reason to like the diagrams is that it leads to correct force diagrams. But the really cool thing is that students were thinking about the roles that both the motor and Brian were playing, which I hadn’t even thought about. It’s not merely preventing mistakes, it is generating insight and ideas about the different roles that interactions play inside, outside, or many degrees removed from a system.
Even if you showed me evidence that teaching system schemas doesn’t improve student learning, I’d still teach using them, because of how generative they are. It helps to create classroom environment in which student insights can be celebrated for what they are, rather than constrained to being misconceptions. By the way, the diagrams do seem to help student learning.
This post represents where we were a week ago. The quotes below show where we are today.
“In the case of the dropping textbook and the ball of paper, the textbook has more weight, but it is more resistant to moving, so it will take the same to hit the ground as the paper (which is less resistant to the downward motion).”
“The gravational pull on the heavier object (the medicine ball) is more than it is one the lighter object (the basketball). The reason why they both hit the ground at the same time is because the inertia on the medicine ball causes it to resist acceleration so it needs more force to come down.”
“The gravitational pull on different objects is not the same. Weight tells us this because the heavier object has the tendency to pull harder towards to earth. Also, the more inertia a certain item has, the harder it is to get it to accelerate and the opposite with lighter objects.”
“Objects that are different weights hit the ground at the same time when dropped from the same height. The heavier object has a lot more inertia (resistance to change in motion), so it takes and effort to get the heavier object to move as fast as the lighter object.”
“Even thought objects accelerate downwards at the same rate, the heavier object takes more force so that both will accelerate at the same constant.”
“I didn’t realize that the bigger ball had more force than the other because it is heavier it apparently has more inertia so it takes more force to pull the ball to the ground. I thought since they both hit the ball at the same rate that they would both have the same forces acting on them the same.”
“So I already knew that both balls were going to hit at the same time, but I didn’t know why. I previously thought that they would fall at the same rate due to same force of gravity. Prior to this class I thought that the heavier ball would fall faster due to the mass. But, heavier ball has a larger force. Although the ball is heavier and has a higher force, inertia slows it down making it land at the same time as the smaller ball.”
“I thought that the two balls had the same force since they hit the ground at the same time. I thought the same force would have to be pulling on them for them to hit the ground at the same time. But I’ve learned that since the ball has a greater mass, then it also has greater resistance to the forces pushing on the ball.”
“It takes more force to get the heavier fall to fall at the same rate”
“Both of the balls have a speed that is constantly changing. Most people think that their speeds were constant but they arent. I also learned that a heavier ball has more of a force than a lighter ball. ”
” I would think that the mass would increase the force, lessening the time it takes to hit the ground, but I am still confused.”
“objects change in speed during free fall, but the acceleration for both of the objects is the same. Also, I learned that if a heavier ball and a lighter ball are dropped at the same time, they will hit the ground together due to the fact that the heavier ball resists acceleration.”
“I thought about the force being greater on the heavier medicine ball, and can see how such a simple question can cause confusion on many levels – because one would think – “Yes, gravity is the same throughout the Earth so obviously they have the same force” type deal ;-)”
“It takes more force to get the heavier ball to accelerate at the same rate.”
“I felt like I knew that they would both hit at the same time however now I do not know exactly why this happens.”
“Even though the medicine ball is heavier than the basketball they still hit the ground at the same time but the medicine ball has more force on it. Even though it has more force it still hits the ground at the same time”
I asked students to watch the Three Incorrect Laws of Motion video and to then discuss each one and how they are different that Newton’s Three Laws:
Here is what one students wrote about Newton’s 2nd Law:
[The incorrect law is that ] an unbalanced force causes an object to move with constant velocity (F=mv). This is untrue because F=ma. Changing the force causes the object to accelerate, so the velocity is changing.
It’s interesting, isn’t it?
My favorite responses from the key-drop at-home experiments… I’m reminded at how complex the task of observation can be.
After the waste basket. I think this will happen because normally when i let things go while running, they tend to fly “backwards”. So if I release the keys in front of the waste basket then the keys will fly backwards into the garbage can… No no no no. I had it backwards. Things released will continue forward. So when I did this I released it from behind the garbage can and it ended up traveled in a bit of an arc into the garbage can.
My keys are pretty heavy, so I’ll choose right above the basket. It worked for me! Landed in the trash can that is, makes sense but if my keys were lighter I would drop them before the trash can so they would arc into it.
After the basket, because I feel like the wind and speed from running forward will drag the keys slightly backwards… It was actually before the basket! I feel now that it is because there is so much momentum moving forward you must drop the keys before
I think that if you are running past the waste basket that you should drop your keys right after you pass the wastebasket. Since you are running forwards the keys will go in a diagonal and go into the basket… No it is not what I expected. The keys would go into the basket if I dropped them before the wastebasket. The keys obviously aren’t going to go backwards when I am moving forwards.
I PREDICT RIGHT ABOVE, BECAUSE YOU WILL BE RIGHT THERE WHERE THE HOLE IS. IT WAS RIGHT AFTER. IT MAKES SENSE, BECAUSE THE MOVEMENT FORWARD MAKES THE KEYS PROJECT BACK A LITTLE BIT.
I asked my roommate, [so-and-so] (she says hi!), to perform this experiment with me. We discovered that we needed to drop the keys before running by the wastebasket in order to make sure the keys landed in the wastebasket. The forward force of running with the keys towards the wastebasket continues slightly when you let go of the keys. Therefore, they continue to travel forward for a short distance while in freefall.
As i thought i had to drop the keys just before i passed the basket so the that they didn’t go past the waste basket. I would like to think that since your carrying the keys they still have a velocity even though their not moving, so once separated from your hand they take on the outside acceleration and start to gain its own velocity for a different direction.
When I got my family involved with this activity, they had predicted that I would have to release my keys right above the wastebasket. They said that the weight of they keys and the momentum wouldn’t matter due to the fact that the keys weren’t being thrown. After testing our hypothesis, we found out that what we originally predicted was right. If you run holding your keys out then you would have to release the keys right above the basket in order for the keys to land in it. Releasing the keys before the box and after the box would land the keys in those spots before or after the box.
Week one standards this summer were the following:
#1: I can re-express quantities using different units
#2: I can distinguish among position, distance and displacement
#3: I can relate an object’s acceleration to how its velocity changes
#4: I understand the direction and signing conventions for acceleration during free-fall
Next time, I want something more like: I can distinguish between average velocity from change in velocity.
There are just too many times that we are thinking through problems by considering these kinds of quantities
1/2 (Δv) (Δt)
The reason I am saying this is because on our first exam, much of the feedback I gave out was about the distinction.