Physics Lab Experiment
Unit 1: Measurement and the Scientific Process
Lab 2: Density
Learning goals: Learn how to perform accurate direct and indirect measurements.
Make measurements with graduated cylinder and beam balance.
Perform basic unit conversions.
Connect a kinetic model of matter to the concept of density.
Purpose: To use the concept of density to explain the phenomena of icebergs (floating ice), convection currents, and salinity driven currents.
Pre-lab Activity:
1. Read the complete procedure. Highlight or underline any section where a measurement must be made. Make note of any section that is confusing and write your questions below.
2. Use the following equation to complete the following problems about density
a. What is the density in g/ml (g/cm3) of a liquid if a volume of 75ml is found to have a mass of 72g?
b. What is density in g/ml (g/cm3) of a cylinder that has a radius of 1.75cm and a height of 12cm?
c. What do you expect the mass (in kg) to be for a block of copper (density 8.94g/cm3) if the measured dimensions are 1m × 0.2m × 0.2m?
3. Describe how the concept of density explains the phenomena of objects floating. How can you determine whether an object will float on water or not?
Density of Room Temperature Water
This procedure highlights an indirect measurement of density. Several known volumes of water are massed. The density found as the ratio of mass to volume by measuring the slope of a mass vs. volume graph.
Room Temperature ______
1. Select a graduated cylinder. Carefully fill with a small amount of room temperature water, taking care to prevent drops from touching the side.
2. Using the meniscus, measure the volume of the liquid.
3. Place the filled graduated cylinder on the balance and measure the mass of the graduated cylinder and the liquid.
4. Add additional amounts of water to the graduated cylinder and repeat both measurements for several quantities of water until the cylinder is full.
Water Volume (mL) / Cylinder & Water Mass (g)5. Create a graph using Logger Pro. Use Volume as the independent variable (x-axis) and Mass as the dependent variable (y-axis).
6. Fit a line to the data. Record both the slope of the line (the density of the liquid) and the y-intercept. What is the significance of the y-intercept?
7. Record the standard deviation of the slope along with the value of the slope.
8. Print the graph for your records.
Slope of Line ______Y-Intercept ______
Density of Room Temperature Salt Water
This procedure highlights an indirect measurement of density. Several known volumes of water are massed. The density found as the ratio of mass to volume by measuring the slope of a mass vs. volume graph.
Water Temperature ______
9. Select a graduated cylinder. Carefully fill with a small amount of salt water, taking care to prevent drops from touching the side.
10. Using the meniscus, measure the volume of the liquid.
11. Place the filled graduated cylinder on the balance and measure the mass of the graduated cylinder and the liquid.
12. Add additional amounts of water to the graduated cylinder and repeat both measurements for several quantities of water until the cylinder is full.
Water Volume (mL) / Cylinder & Water Mass (g)13. Create a graph using Logger Pro. Use Volume as the independent variable (x-axis) and Mass as the dependent variable (y-axis).
14. Fit a line to the data. Record both the slope of the line (the density of the liquid) and the y-intercept. What is the significance of the y-intercept?
15. Record the standard deviation of the slope along with the value of the slope.
16. Print the graph for your records.
Slope of Line ______Y-Intercept ______
Density of Ice Water
This procedure highlights an indirect measurement of density. Several known volumes of water are massed. The density found as the ratio of mass to volume by measuring the slope of a mass vs. volume graph.
You will want to work as quickly as possible while remaining accurate. Why do you think this is important for this particular measurement?
17. Select a graduated cylinder. Carefully fill with a small amount of ice water, taking care to prevent drops from touching the side. Make sure there is no actual ice in the water.
18. Using the meniscus, measure the volume of the liquid.
19. Place the filled graduated cylinder on the balance and measure the mass of the graduated cylinder and the liquid.
20. Add additional amounts of water to the graduated cylinder and repeat both measurements for several quantities of water until the cylinder is full.
Water Volume (mL) / Cylinder & Water Mass (g)21. Create a graph using Logger Pro. Use Volume as the independent variable (x-axis) and Mass as the dependent variable (y-axis).
22. Fit a line to the data. Record both the slope of the line (the density of the liquid) and the y-intercept. What is the significance of the y-intercept?
23. Record the standard deviation of the slope along with the value of the slope.
24. Print the graph for your records.
Slope of Line ______Y-Intercept ______
Density of Near Boiling Water
This procedure highlights an indirect measurement of density. Several known volumes of water are massed. The density found as the ratio of mass to volume by measuring the slope of a mass vs. volume graph.
You will want to work as quickly as possible while remaining accurate. Why do you think this is important for this particular measurement?
Water Temperature ______
25. Select a graduated cylinder. Carefully fill with a small amount of near boiling water, taking care to prevent drops from touching the side.
26. Using the meniscus, measure the volume of the liquid.
27. Place the filled graduated cylinder on the balance and measure the mass of the graduated cylinder and the liquid.
28. Add additional amounts of water to the graduated cylinder and repeat both measurements for several quantities of water until the cylinder is full.
Water Volume (mL) / Cylinder & Water Mass (g)29. Create a graph using Logger Pro. Use Volume as the independent variable (x-axis) and Mass as the dependent variable (y-axis).
30. Fit a line to the data. Record both the slope of the line (the density of the liquid) and the y-intercept. What is the significance of the y-intercept?
31. Record the standard deviation of the slope along with the value of the slope.
32. Print the graph for your records.
Slope of Line ______Y-Intercept ______
Density of Ice
This procedure highlights an indirect measurement of density. Several known volumes of water are massed. The density found as the ratio of mass to volume by measuring the slope of a mass vs. volume graph.
Your instructor will provide a large piece of ice for you to work with. Only ask for the ice when you are ready to make your mass and volume measurements. Work with it quickly, then return the ice to the instructor for storage.
33. Set up an overflow container so that the overflow will be collected in a graduated cylinder.
34. Remove the graduated cylinder from the setup and fill the overflow container with ice water until it begins to overflow. Clean up any mess.
35. Replace the graduated cylinder.
36. Collect the ice and measure its mass.
37. Carefully set the ice in the overflow container and, using a pair of forceps, carefully submerge the ice completely.
38. Remove and return the ice.
39. Measure the volume of water displaced by the ice. This will be the volume of ice.
Ice Volume (mL) / Ice Mass (g) / Density of Ice (g/mL)
Summary of results.
Ice
Ice Water
Water at Room Temp.
Water near Boiling
Salt Water at Room Temp.
Lab Questions:
1. Create a graph of density vs. temperature for the fresh water and ice measurements. Select a scale that will “bring out” the differences rather than show the similarities. Include error-bars indicating the standard deviation when available. Sketch in a best fit line. Add a point to the plot for the salt water measurement.
2. Use your data to create a hypothesis explaining the phenomena of “convection currents” that exist in a pot of water above a flame (illustrated below).
3. Use your data to create a hypothesis explaining the phenomena of icebergs. What prediction could you make about how high an iceberg would float in salt water and fresh water of the same temperature?
4. Use your data to predict how the salinity (saltiness) of the ocean might vary with depth. How does your prediction compare to the data at (link on website also): http://www.windows.ucar.edu/tour/link=/earth/Water/salinity_depth.html&edu=high
5. A sample of warm, high salinity water is observed near the surface of the ocean. The water 500m below is observed to be both less salty and cooler. Think about the changes in density you observed as a result of changing temperature and salinity. Which effect, temperature or salinity, is most important in causing this observation? Why?
6. How does the kinetic theory of matter relate to your observation of water’s changing density as temperature increases?
The “global conveyor belt” is a worldwide ocean current driven by temperature and salinity (see link on site or below). It is an interesting phenomena that can be understood using the work you’ve done here.
http://nasascience.nasa.gov/earth-science/oceanography/physical-ocean/salinity