OK, unless I get hit by a truck, I will be back on Thursday.
Today, please work together to help all students complete their data collection and analysis Data analysis should include:
Description of each type of collision/explosion you created.
A list of the percent momentum and percent kinetic energy lost during each event.
Hint: Once you get your data entered into your spreadsheet, you should be able to calculate momentum and kinetic energy from the same cells for each event.
This is where consistency in your layout makes formula (equation) writing easy. Once you write the formula, just copy/paste to the needed cells.
Calculate the average momentum and kinetic energy lost for all your events.
Remember to submit your spreadsheets below. I’m still missing a few.
My lengthy illness (severe sore throat, doc says it’s not coronavirus, but I did get tested for strep today) has presented an opportunity that I have always wanted to do, but never had the nerve to go through with:
Set a class to work on a topic and let them work it out with each other until they have it right, with no instruction from me (well, I have provided direct instruction last Monday and Tuesday, as well as some online videos and other tips).
I see you get down to work on whiteboards to solve problems from the book, but when you get your hands on equipment, many of you get frustrated when it gets hard.
Today’s the day to put all your brains together!
If your group has a lot done, collaborate with other groups to help them along.
Ask yourself what it is you are trying to measure, then decide how the equipment will get you that measurement.
Don’t worry about making a mistake; you may have to repeat yourself, but you can’t really break the equipment.
In the end, if you can work your way through this somewhat complex experiment, the ‘grit’ and collaborative skills you develop will be much more valuable than any physics you learn in here.
Don’t give up! You are all intelligent people who can figure it out.
You’ve probably heard about grit and perseverance, but here’s a short video that you might want to watch for more info:
“Gritty people train at the edge of their comfort zone.”
Here’s a video to show you two different ways to think about momentum, using Newton’s laws and Galilean relativity.
Here’s one telling you all about the units and equation for momentum.
Hi all. I’m out for another day or two (extreme sore throat, no, not caronavirus!) From the feedback I’ve received on Remind, it looks like most groups have completed, or are successful at gathering, the data.
Please take Monday to complete gathering data and entering it into a spreadsheet.
I’m proud of you all working together to figure out how to work the photogates and collect the data. It’s unusual for you to have this many days without your regular teacher, and it seems you are doing a great job.
It looks like some of you tried to copy the spreadsheet template on Friday, but were not logged in to your school account. I have set the sharing so you can now access it from any Google account. Click here if you need it.
Today: Enter a link to your spreadsheet in the form at the bottom (even if you have not completed it).
Here’s a screenshot of the template. There are no formulas written, so you will have to write those yourself. Remember that each students needs to have their own copy of the spreadsheet.
Please finish data collection for both collisions an explosions. Remember that an explosion uses the spring on one cart, and both carts start with zero momentum.
Data analysis
Analyze all your trials, calculating the momentum and kinetic energy changes for each scenario. If you would like, you can use a Google spreadsheet template here.
Each member of the group needs to make their own spreadsheet. If you prefer to use Excel, you can download the Google Sheet as an Excel spreadsheet.
Homework
Complete all the data analysis in a spreadsheet, and develop a conclusion about the conservation of momentum and kinetic energy in each of your scenarios.
Review your lab goals and procedures from Tuesday’s description. Your goal today is to collect pre- and post- collision data for both of your carts in four different variations (e.g. changing the mass, changing the velocity, changing the direction of the cars).
Data collection
Set up your ramp so you can record the data both before and after the collision.
Before you start collecting data, make a bullet list of all the variables you will measure. Include the following for each variable:
where you will find that number (on what device)
the units for each measurements
the uncertainty of each measurement (remember that with digital readouts, we assume ±1 of the lowest decimal place provided by the measuring device).
Create a data table in your lab book, including three trials for your four different collision types.
Collect your data, then enter it into a Google or Excel spreadsheet (we will want to do more processing of the data than Desmos can handle, although you may want to ‘copy and paste’ the data into Desmos later for plotting).
After you have completed collecting data for your four collisions, start with your explosion data collection if you have time.
The Vernier Photogates use a beam of light to detect objects between the two ‘arms.’ LoggerPro identifies the gate state as “Open” or “Closed.”
Open implies that nothing is blocking the light beam
Closed implies there is something blocking the light beam.
In most cases, we want to know the time that the gate is closed.
Determining the speed of an object that passes through the photogate
Attach a photogate to a ringstand, then adjust it so a flag mounted on your cart will break the beam of light.
Measure the length of the object that will pass through photogate. When the object passes through the photogate, it measures how long the beam is blocked. The object’s speed (at the position of the photogate) is determined by dividing the length of the object by the blocked time.
This video should walk you through setting up Logger Pro for ‘gate timing.’ The interface she uses different than our LabQuest Mini, but the sensor set up should be the same.
Remember that you will need to attach both photogates, so you can get the velocity of each cart.
More detailed information on the photogates can be found on Vernier’s website.
Here’s a video with more deep background on how the Photogate works.
These labs will take about three days to complete. Tuesday will be preparing/practicing. Wednesday will be completing Part 2 and 3. Thursday will be sharing your trends/conclusions with the class, where we will look for overall trends/conclusions.
Prelab discussion (much yesterday)
Part 1: Qualitative construction of momentum
Part 2: Collision of Carts
Part 3: “Explosion” of Carts
Postlab discussion
Part 2: Collision of Carts
You will be provided with two carts and various masses. You will need to measure the speed of the carts right before they collide and right after they collide.
Working with your group (record all in your lab book):
Develop a method of measuring/calculating the velocity of two carts right before and after they collide.
Practice with your method until you are confident you can accurately measure the needed velocities.
Determine the uncertainty in each of your measurements.
Plan out at least four different types of collisions. This may involve
Initial directions
Masses
Develop a data table to record your data for all your variations.
Run your trials.
Analyze your data
Present trends in a reflection section.
Part 3: Explosions
Explosions are defined as interactions where the initial velocity of each cart is zero.
Repeat the steps you used for Part 2
Video tutorial
Just a fun video showing Newton’s Cradle made with bowling balls!
Momentum is a conserved property of a system. This conservation can be demonstrated by using Newton’s third law (Fa/b = -Fb/a) to develop the equation:
mΔva + mΔvb = 0
Momentum is given the lowercase p as its symbol.
The change in momentum (Δp) of an object is defined as impulse.
Impulse = Δp = mΔv = FΔt
Keep in mind that while momentum depends on the same variables as kinetic energy (mass and velocity), momentum and kinetic energy are not the same thing.Momentum is always conserved, but, while energy is conserved, it can move from kinetic storage storage to gravitational, elastic, thermal, etc.
