Archive for March 2009
I’ve been doing this lab for a number of years, but it needed a make-over. I did that today, it’s beefed up a little and I added a data sheet. I’ve gotten away from the lab notebooks because they are just too hard for me to collect and take home, and I never seem to be able to grade at school. I’ve headed towards more of a “min-lab” format that I read about in The Physics Teacher a year or two ago. This has greatly cut down on my grading, which allows me to do more lab and hands-on work, which gives me more to grade. Somewhere in there we reach equilibrium.
This lab uses two double pulleys, some mason line, a ring stand and ring, spring scales, a meter stick and a weight. I like to use a 1 kg weight. It’s heavy enough that they can feel the difference when the pulley helps out, but not so heavy that everything is falling over. I found it helpful to have two or three different size strings. The short string for the first three configurations is about a foot long. They then switch to a second string that is four or five feet long. I would suggest you play with the lab and then make up the appropriate length strings. I like the pink mason line, it’s easy to see from across the room, so I can tell what’s going on at every work station. It’s also easy to find when things are misplaced.
Here is the lab and data sheet:
I would love suggestions and ideas to improve this lab. I’m still not thrilled with the overall lab, but it’s the best I’ve been able to do so far.
Long story short, we went to Penn State, visited the nuclear reactor, toured the school, ate lunch, and purchased two coolers full of ice cream. It’s a 3+ hour ride home, so we also purchased dry ice for $0.75 per pound.
The next day, there was still quite a bit of dry ice left over, so I did this demo for each of my classes. I put the dry ice in water and watched the “smoke” pour out. I had another beaker with water and some dish soap. Adding dry ice to that makes a huge pile of bubbles that are cloudy and evaporate on contact.
The best part was that the kids suddenly had a ton of questions. They wanted to know what would happen if they inhaled the gas, if the water was safe after the dry ice was gone, and lots more. Don’t forget to play, it’s a great way to learn.
I developed this lab for my physical science classes, but I wish I had thought of it for my physics classes. Since we do more with the coefficient of friction in physics, I will be upgrading and adding this lab to my course for next year.
In this lab, the students pull various objects across different surfaces. The objects pulled were what I could get my hands on in a very short amount of time. I had wooden blocks, plastic coated weights, steel weights, aluminum ringstand rings, and I asked the students to also use their sneakers.
They pulled these objects across a whole range of surfaces. They used the top of the desk, the floor tiles, cardboard, plywood, tile board (white board), a rubber coated lab apron, cork board, and Styrofoam sheets. I asked them to get creative and find objects and surfaces in the room. I didn’t have sandpaper out, but many of them asked for it in their write-up. The plan was to pick an object, pull it across as many surfaces as possible, then move on to another object.
They were surprised at the stickiness of the aluminum ring on the shop apron. I was too, it had a coefficient of friction greater than 0.5.
When I do this with my physics students, I will probably add a component where they have to predict the maximum angle of incline for an object on a surface before it starts slipping. I like that.
Here’s my lab paper: measuring-the-coefficient-of-friction1
We just did this lab yesterday and today. It took the whole 50 minute period yesterday plus about 20 minutes today. The feedback I got from the students was really great. We studied torque in the classroom first, solved some problems, then did this lab. They felt that they understood torque after completing the lab. I came up with the lab in the shower in the morning (all of my great ideas and life solutions appear when I’m in the shower) and I wrote the whole thing up in my prep period before their class. So much for planning ahead.
The lab uses a ring stand and support. I have pendulum attachments for ring stands, but a regular ring will work just fine. Using a meter stick, string, and some weights, they first create a balanced system with no net torque. They then calculate the torque in each direction to show it is balance. They do this with two weights and then with three.
Next, they pick a location for one weight and have to determine where the second weight goes to balance the system. They know they get it when the meter stick balances right away. Again, they repeat this with three weights.
Lastly, they move the fulcrum so the stick becomes part of the problem. You can read the details in the lab, I think it’s fairly clear.
My lab sheets are here, feel free to use it as-is or modify them:
This is one of my favorite simple demonstrations. I have a plastic spool that came from a pack of rope lights. The spool is about a foot across and I use it regularly to demonstrate a constant horizontal velocity.
When we study torque, I attach a pink mason line to the spool and wind it up. The question for the kids is, “What happens when I pull on the string?” Now, if it is unwinding from the top, obviously the spool is going to go in that direction. In the case of the drawing on the right, the spool is going to roll to the right.
But what happens when the spool unwinds from the bottom? Most of the kids think it is going to move to the left. A few will guess that it will stay in place, unwinding and slipping at the same time. Only a few think it will move to the right.
It does in fact move to the right. If we consider the point at which the spool meets the table our fulcrum, then we have a torque causing clockwise rotation according to the drawing at the right. The force is going to wind the string around the spool. Don’t believe me, try it for yourself.
I’ve been searching for a projectile motion activity/lab for my physical science class. I completely forgot about this one, and I’ve done it for years. We are going to make catapults from popsicle sticks, hot glue, rubber bands, and a spoon.
I like this lab because the hot glue allows for rapid build and repair, and there is a definite need for repair and modification in this project. The kids typically build the frame from the popsicle sticks and then try to attach the spoon with rubber bands. The spoon is the launcher for the catapult. Usually, they find there is no way to connect the rubber bands, so they start adding little posts. The next problem they encounter is the rubber bands aren’t tight enough so the object doesn’t launch very far. They then tighten the rubber bands and the frame starts to collapse. So they need to go back and reinforce the frame.
At this point one of three things happens.
- The catapult is improved and they start launching marshmallows.
- They realize they can rebuild the catapult rather quickly and so start all over and improve their design.
- The catapult falls apart, they attempt improvements, but basically give up.
The picture isn’t a great example, but it is a starting point.