What A Drag!
Related Links
Project Summary
| Difficulty | 4 |
| Time required | Very Short (a day or less) |
| Prerequisites | None |
| Material Availability | Readily available |
| Cost | Very Low (under $20) |
| Safety | No issues |
Sponsor
| Sponsored by a generous grant from Northrop Grumman Foundation |
|
 |
| Weightless Flights of Discovery Program for Teachers |
| www.northropgrumman.com/ community/weightless.html |
Objective
In this experiment 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 which act upon them: lift, weight, thrust, and drag (FI, 2006).
 |
| 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 it is moving through. This is often called air resistance. For an object moving through the water, drag is caused by friction between the object and the water it is moving through. The force of drag is important for both the aerodynamics and hydrodynamics of a design.
In this experiment 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 hydrodynamic?
Terms, Concepts and Questions to Start Background Research
To do this type of experiment 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!
- hydrodynamics
- aerodynamics
- friction
- drag
- What causes drag?
- How does drag influence the aerodynamics of an object?
- Which objects will produce the most drag?
Bibliography
- FI., 2006. "Forces of Flight," The Franklin Institute Science Museum, Philadelphia, PA. [Accessed December 15, 2006] http://www.fi.edu/flights/own2/forces.html
- FI., 2006. "Forces of Flight - Drag," The Franklin Institute Science Museum, Philadelphia, PA. [Accessed December 15, 2006] http://www.fi.edu/flights/own2/drag.html
- Rader, A., 2006. "Motion: Forces," Physics4Kids.com [Accessed December 15, 2006] http://www.physics4kids.com/files/motion_force.html
- Rader, A., 2006. "Motion: Vectors," Physics4Kids.com [Accessed December 15, 2006] 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.
Materials and Equipment
- scissors
- fishing line
- leader line
- spring scale
- swimming pool
- fishing swivels
- objects to test:
- spheres (baseball, grapefruit, orange...)
- rectangular shapes (cubes, plastic blocks, boxes, brick...)
- circular shapes (frisbee, plate, cd...)
- irregular shapes (toy, pipe, hammer, jar, boomerang...)
Experimental Procedure
- Select several objects that you want to use for your experiment. The objects should be medium-sized (so that they are easy to handle) and water-proof (because you will be submerging them in a pool of water) to work well in this experiment. They should also be objects that will naturally sink and not float. For example, choose a baseball instead of an air-filled ball so that it will sink.
- 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.
- Attach a leader line to the spring scale. It should be long enough for your object to reach down into the pool while you are walking along the edge of the pool while holding on to the spring scale handle.
- Attach each item to the leader line of the spring scale one at a time.
- Walk from one end of the pool towards the other at a constant stride, pulling the item behind you submerged in the pool. It will be important to walk at the same speed for each item.
- Look at the spring scale and record the force of each item in a data table:
Trial Number Baseball Toy Airplane Frisbee Plastic Block 12345678910Average Force (N)Resting Force (N)Drag (N) - To be sure that the results are meaningful, you will want to repeat the measurement for each item at least ten times, then you will make an average of your data by adding together all ten trials and dividing your answer by ten.
- 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 in your data table.
- Next, subtract the Resting Force from the Average Force to get your final estimation of the amount of drag for each object.
- Make a graph of your data. 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.
- Analyze your data by asking yourself some questions. Which object caused the most drag? The least? Are some shapes better than others? Are some sizes better than others?
Variations
- In this experiment 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?
- For more science project ideas in this area of science, see Aerodynamics & Hydrodynamics Project Ideas
Credits
Sara Agee, Ph.D., Science Buddies
Last edit date: 2007-03-09 12:00:00
