# 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.

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 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.

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 Measuring specific gravity with a U-tube manometer

Here is an animated GIF of the tube filling from the “measuring specific gravity with a U-tube manometer” demonstration. The full video is here.

Don’t try this alone, it really takes two people to do the filling.

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. If you do not wish to register with twitter or wordpress to get updates then send me an email and I will add you to the list I send update notifications to.

# Measuring specific gravity of oil with a U-tube manometer

This is a really simple demonstration that allows you to measure the specific gravity of oil using a u-tube manometer. It also gives students the opportunity to visualize a multi-fluid manometer.

Equipment

1. A 4 foot length of clear flexible tubing with a diameter of about a half to one inch
2. A funnel
3. A bucket of water
4. A jug of oil (cheap cooking oil is perfect)
5. A tape measure or ruler
6. A chalk or white board with appropriate marker.
7. A student volunteer

Demonstration

1. Draw a horizontal line on the board.
2. Hold the tubing at each end forming a u-tube.
3. Have the student pour water into the tube until there is about 9 inches of air between the top of the water and the top of the tube ends
4. Show the students that the water levels are at the same height on both sides of the u-tube
5. Have the student slowly pour the oil into one side of the u-tube until there is about 2-3 inches of air between the top of the oil and the top of the tube.
6. Hold the u-tube up so that the bottom of the column of oil is at the height of the line drawn on the board.
7. Measure the height of the column of oil (Hoil) and the height of the water (Hwater) above the same horizontal line.

Analysis

Because hydrostatic pressure does not vary horizontally across the connected water, the pressure in the u-tube at the height of the line on the board is the same on both sides. Starting at the oil free surface you can write that the pressure at the line is

Plineoil g Hoil

The pressure at the line can also be calculated starting at the free surface of the water,

Plinewater g Hwater

Equating these two pressures gives

Plinewater g Hwateroil g Hoil

which can be re-written as

S.G.oiloilwater= Hwater/Hoil

For the example in the pictures the depths were Hwater=15cm and Hoil=18cm such that S.G.oil=0.83. You can then compare this to online data tables for various oil densities.

The demonstration is also good for discussing measurement errors as there is error in both height measurements. Re-doing the S.G. calculation with, for example, the low estimate of Hoil and the high estimate of Hwater (or vice versa) will give a different result. In this case the uncertainty in the measurement is at least 0.5 cm so the S.G ranges from 0.78 to 0.89.

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. If you do not wish to register with twitter or wordpress to get updates then send me an email and I will add you to the list I send update notifications to.