Take home lab – Personal specific gravity

This is a fun take home lab as the students have to measure themselves. It is also a lab in which the student should know roughly the answer before they start. Generally speaking, most people either just float or just don’t and therefore their specific gravity should be approximately S.G.=1. As with all the take home labs the students are required to use more than one method. The fundamental problem is measuring a person’s volume. There are a range of methods for doing this which often have significant uncertainty/error. There is, therefore, the possibility of having significantly different values from the two different measurements that must be reconciled through the error analysis.

When giving this as a take home lab I have generally found that the students are able to find two, and sometimes more, ways of doing the measurements. The students also sometimes borrow methods they learned about in other classes such as their materials lab. Once a team even worked out how to measure their submerged weight. It is a nice introductory take home lab as the measurements are easy to make but have significant uncertainty. Therefore, it is a good platform for discussing error analysis before they get into the more complex take home labs to follow.

As with all the take home labs I will not publish detailed methods for conducting the tests as I still use them in class and want my students to figure it out on their own.


Instructions to students

Introduction

The specific gravity of a fluid is its density divided by the density of water. But specific gravity is not unique to fluids. Your goal is to calculate the specific gravity of one of your team members using at least 2 different approaches.

Task

  1. Run a series of experiments to establish the specific gravity of either a member of your team or the team as a whole (or both if one particular method suits an individual test and the other suits a group test).
  2. Write a brief report that
    • Is 3 pages max including photos of you running your experiments.
    • Describes the experiment(s) you used to establish your result including:
      1. How the test was run.
      2. What data you collected.
      3. How you performed your calculations including diagrams, equations, and relevant theory that has been covered in in this class.
      4. A quantitative discussion of the uncertainties in your measurements and calculations including an analysis of the differences between your two sets of measurements.

Due in 2 weeks


An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Take Home Lab – Measuring the mass flow rate from a compressed air can

The mass flow rate of a fluid appears many times in an introductory fluids class (pump power, conservation of mass, momentum, etc.). This take home lab requires students to use at least two different approaches to measure the mass flow rate out of a compressed air can. My experience with this is that some students struggle with finding a second way to do the measurement. This has led to some rather creative, if not physically appropriate, measurement methods.

It is a nice experiment because there are substantial difficulties in taking accurate measurements. For example, it is hard to accurately measure the diameter of the straw connected to the can as it is so small. It is not unusual to have a measurement uncertainty of 50-100% in the diameter leading to an error/uncertainty of up to 400% for the straw area. These errors  can make a substantial difference to the resulting calculated mass flux. There can, therefore, be substantial differences between the two sets of measurements that are still within the bounds of uncertainty. There is also a repeatability problem with this lab that is easily observed and explained if one is paying attention to the data.

air can

As with other take home labs that I use later in the semester, the students are required to do some basic error analysis to explain the differences between their two measurements. This is a very useful complement to their fluids lab class that runs in parallel with the main lecture class. The students need to estimate the uncertainty in each measurement they take and then use that data to estimate the uncertainty in their measured mass flow rate.

As with all the take home labs I will not publish details on specific methods for conducting the tests as I still use them in class and want my students to figure it out on their own.


Instructions to students

Introduction

 In this class we have looked at a range of different flow analysis techniques. In this lab you need to use 2 different approaches to estimate the mass flow rate coming out of a compressed air can such as are used for cleaning computer keyboards.

Task

  1. Run a series of experiments to establish the mass flow rate out of a compressed air can. You can borrow an air can from me when you are ready to do your testing. You may use an electronic scale and a stopwatch but otherwise only non-lab equipment is to be used without permission. If you would like to use something else you need to check with me.
  2. Write a brief report that
    1. Is a maximum of 3 pages including photos of you running your experiments.
    2. Describes the experiment(s) you used to establish your result including
      1. How the test was run
      2. What data you collected including estimates of your measurement uncertainty
      3. How you performed your calculations including diagrams (with control volumes), equations, and relevant theory
      4. A quantitative discussion of the uncertainties in your measurements and calculations including an analysis of the differences between your two sets of measurements.

Due in 2 weeks


An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Take home lab experiment – Ranking of common fluids by density

This is a very simple take home lab to get students started into the semester. They are asked to use three different techniques to rank a range of common fluids (that can be found in one’s home) by their density . There are a broad range of approaches to this including directly measuring their density, using buoyancy, using multi-fluid manometers, or simply stacking them up. However, there are also some tricks to this as well. For example, it is easy to end up with two or more of the fluids being miscible making it hard to float one on the other. It is also a great introduction to quantifying errors. Many common fluids are quite close in density so often the student groups would get different rankings from their different experiments. This illustrates that even simple measurements have error/uncertainty associated with them. This provides a great motivation for discussing measurement errors and resulting calculation uncertainty (though at the start of the semester I typically only discuss measurement error and move onto error analysis later).

As with all the take home lab write ups I will not publish detailed methods for conducting the tests. I still use them in class and want my students to figure it out on their own. The instructions I give to students are below.


 Introduction

As we have seen in class different fluids have different densities. Density is a fluid property that varies with temperature (and pressure but not very much). Accurately measuring the density of a given fluid can be done in many ways and you are welcome to research this as part of this assignment.

Task

  1. Identify 5 common fluids that you find in everyday life (kitchens are a good place to start)
  2. Run a series of experiments to establish their relative densities (that is, rank them by their density)
  3. Use three different experimental techniques to establish this ranking.
  4. Write a brief report that
    1. Is 2 pages max including photos of you running your experiments
    2. Describes the experiments you used to establish your rankings
    3. Includes a table of fluids ranked by density

Rules

  1. You may not use equipment in the fluids lab or any other scientific lab equipment
  2. You should only use items that are commonly available in your home
  3. If you need to go to a store to buy something please come and see me first. I may be able to lend you something or I will buy it and then lend it to you. You will need to explain why you need it and it should be cheap.

Due in 2 weeks


 

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.

Video of “Bernoulli and collapsing paper tents” demonstration

Here is a video of the “Bernoulli and collapsing paper tents” demonstration. The full video can be found here.

tent

An index of all the demonstrations posted on this blog can be found here. Don’t forget to follow @nbkaye on twitter for updates to this blog. If you have a demonstration that you use in class that you would like to share on this blog please email me (nbkaye@clemson.edu). I also welcome comments (through the comments section or via email) on improving the demonstrations.