Abstract

Objective

In this science fair project, you will test ordinary objects for their aerodynamic and hydrodynamic properties by measuring the amount of drag they have.

Introduction

Moving objects appear to glide gracefully through the air or water. But in reality, moving objects are constantly fighting to balance the forces around them. Moving objects have four main forces that act upon them: lift, weight, thrust, and drag (FI, 2006).

Figure 1. The aerodynamics of this airplane are due to the balance of four forces: lift, weight, thrust, and drag (FI, 2006).

One way to think about the force of drag is to think of it as a force of friction. For an object moving through the air, drag is usually due to friction between the object and the air through which it is moving. This is often called air resistance. For an object moving through the water, drag is caused by friction between the object and the water through which it is moving. The force of drag is important for both the aerodynamics and the hydrodynamics of a design.

In this science fair project, you will test how much drag ordinary objects produce when pulled through the water. You will make a simple device to measure the drag by using a pull-scale and fishing line. After testing different objects around your house, will you be able to find out what types of objects move smoothly through the water? Which shapes are the most aerodynamic and the most hydrodynamic?

Terms, Concepts, and Questions to Start Background Research

To do this type of science fair project, you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• Drag
• Friction
• Air resistance
• Aerodynamics
• Hydrodynamics

Questions

• What causes drag?
• How does drag influence the aerodynamics of an object?
• Which objects will produce the most drag?

Bibliography

• The Franklin Institute. (2006). Forces of Flight. Retrieved December 15, 2006, from http://www.fi.edu/flights/own2/forces.html
• The Franklin Institute. (2006). Forces of Flight - Drag. Retrieved December 15, 2006, from http://www.fi.edu/flights/own2/drag.html
• Andrew Rader Studios. (2006). Motion Basics. Retrieved December 15, 2006, from http://www.physics4kids.com/files/motion_force.html
• Andrew Rader Studios. (2006). Motion: Vectors. Retrieved December 15, 2006, from http://www.physics4kids.com/files/motion_vectors.html
• Sobey, E., 1999. Wacky Water Fun with Science, New York, NY: McGraw-Hill.
• Sobey, E., 1998. Just Plane Smart! Activities for Kids in the Air and on the Ground, New York, NY: McGraw-Hill.

For help creating graphs, try this website:

• National Center for Education Statistics. (n.d.). Create a Graph. Retrieved May 27, 2009, from http://nces.ed.gov/nceskids/CreateAGraph/default.aspx

Materials and Equipment

• Scissors
• Fishing line
• Leader line
• Spring scale
• Swimming pool
• Fishing swivels
• Objects to test, with the following features:
  • You should use several different types and sizes of each.
  • They should not be so large that they are difficult to handle.
  • They should all be waterproof, because you will be submerging them in a pool of water.
  • They should be objects that naturally sink and not float. For example, choose a baseball instead of an air-filled ball so that it will sink.

  Use objects of the following shapes:

  • Spheres (baseball, grapefruit, orange, etc.)
  • Rectangular shapes (cubes, plastic blocks, boxes, brick, etc.)
  • Circular shapes (frisbee, plate, CD, etc.)
  • Irregular shapes (toy, pipe, hammer, jar, boomerang, etc.)
• Lab notebook
• Graph paper

Experimental Procedure

1. Select several objects that you want to use for your science fair project, as described in the Materials and Equipment list, above.
2. Wrap fishing line securely around each object. Make a loop out of fishing line at the leading edge of the object and attach a swivel hook. This will be where you attach the leader of the spring scale to each object. Have an adult help you, if necessary.
3. Attach a leader line to the spring scale. It should be long enough for your object to reach down into the pool as you are walking along the edge of the pool, and while you are holding onto the spring scale handle.
4. Attach an item to the leader line of the spring scale.
5. Walk from one end of the pool toward the other end at a constant stride, pulling the item behind you, as it is submerged in the pool. It is important to walk at the same speed as you drag each item.
6. Look at the spring scale and record the force of the item in a data table, like the one below, in your lab notebook.

This is an example of how to organize your data in your lab notebook.

7. Repeat steps 5–6 for the first object, at least 10 times to be sure that the results are meaningful.
8. Repeat steps 4–7 for all of your other objects.
9. Average your data by adding together the numbers for each object for all 10 trials and dividing your answer by 10. Record all data in your data table.
10. What if your objects each weigh differently? Won't the heavy objects have more drag than the light objects? Since you are testing for shape, you will need to scale your results so that differences in weight are not a factor. To do this, measure the resting force of each object by attaching the object directly to the spring scale and holding it suspended in the air. Record the force, in newtons (N), in your data table.
11. Next, subtract the Resting Force from the Average Force to get your final estimation of the amount of drag for each object.
12. Make a graph of your data, either on paper, or with a website, such as Create a Graph. A bar graph will work well for this type of experiment. Make a scale of the force of drag, in newtons, on the left side of the graph (y-axis) and order your differently shaped objects on the bottom of the graph (x-axis). Draw a bar for each item up to the matching force of drag measured in the pool with the spring scale. Be sure you remember to label the axes and the bars of your graph, and to give your graph a title.
13. Analyze your data by asking yourself some questions. Which object caused the most drag? The least? If you compare across objects of different shapes, are some shapes better than others? If you compare within a group of similarly shaped objects (for example, all spheres) are some sizes better than others?

Variations

• In this science fair project, the items you chose are not of the same shape or size. This means that they may also have different weight and volume. Measure the volume of each object by submerging the objects in a tub or bucket with marked volumes and calculate the difference in water level before and after. Measure the weight of each object by using a kitchen scale. Will the weight and volume of your objects help explain your results?
• Another factor in the aerodynamics or hydrodynamics of an object is the orientation of the object. Is the object moving forward, backwards, sideways, up, or down? You can use the same object in each experiment, but change the orientation, or direction, of the object as it moves through the water. Will the object be more or less dynamic when in different orientations?
• If you’re interested in a more mathematical explanation of your results, try looking up references for the drag equation and thinking about the objects’ cross-sectional areas and drag coefficients.

• For more science project ideas in this area of science, see Aerodynamics & Hydrodynamics Project Ideas.

Credits

Sara Agee, PhD, Science Buddies

Last edit date: 2009-05-27 17:42:00