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Drag Experiment
This is an interesting experiment to see how the drag of your clothes makes a difference when you go swimming.
Did you know that swimming isn't just about skill and athleticism? The human body has skin, contours, and curves. How the water moves along your body and the clothing you wear determines how fast you can go.
Objective
Investigate the effects of a force called drag. Find a swimming pool that is at least 25 meters in length during a time when it is not crowded. Compare the time it takes to swim 25 meters in a swimsuit versus swimming the same distance in full clothing to discover how each affects swim times.
Introduction
The field of Biomimetics is a science based on nature, to improve human life. The word biomimetic is derived from bios, meaning "life," and mimesis, meaning "to imitate".
A company that was inspired by nature to get ideas is Speedo, the swimsuit manufacturer. They looked to the shark to find out what it is about shark skin that makes the shark move so fast.
It turns out that shark skin is made up of denticles that force the water into a tubular flow.
This separates the shark from the water and reduces drag so that the shark can swim fast.
What is drag?
Drag is a mechanical force that is generated by the interaction and contact of a solid body with a fluid. Drag is also the resistance to the motion of a solid body through a fluid. The fluid can be a liquid or a gas. Engineers who design cars, ships, and airplanes always test their designs to see how drag affects their movement.
But what does drag have to do with swimming fast? Human skin and hair interact with water and generate drag that will slow a swimmer down. Speedo has designed suits that reduce drag on the swimmer's body, and repel water. This adds up to faster swim times.
Properly fitting swim suits can reduce your drag and reduce fatigue by minimising unwanted muscle vibration, thereby improving your efficiency. In fact, many of the swimmers who broke records at the 2008 summer Olympics wore the Speedo Fastskin LZR Racer suit. That was exciting. In an attempt to bring boredom back to swimming competitions, FINA banned these suits. Who cares?
We're more interested in the drag effect clothes have when swimming.
For instance, a mesh shirt has a relatively large surface area
and thus should cause a fair amount of drag.
Materials and Equipment
Make sure to take all your materials with you when you go for your swim trials.
- Stopwatch
- Lab notebook
- Swimsuit, close-fitting
- Mesh shirt and shorts
- Jogging suit or tracksuit or jeans and hoodie
- Swimming pool where you can swim 25 meters
without any barriers or interruptions
Get a friend as volunteer to note down your results for later analysis. Find swim buddies who take the test with you. That will be a lot more fun and you can compare results.
Experimental Procedure
Go to your local swim club or pool and speak to the supervisor about your project. Ask what the best time would be to conduct your tests when the pool is not crowded.
Ask how long the pool is. You should swim at least 25 meters to get good useful results.
Note: Rest at least 10 minutes between trials! Perform some warm-up exercises before you start the swim. Remember to swim as fast as you can. Improve your swim times by picturing a shark swimming behind you!
Start your Swim Test
Have your volunteer time how long it takes you to swim 25 meters and record the data in your lab notebook in a data table like the one shown below.
First test your speed in your swimwear. Repeat in mesh shirt and shorts.
| Swim in Swimsuit or Shirt and Shorts | ||
|---|---|---|
| Trials | Swim Time | Speed |
| Trial 1 | ||
| Trial 2 | ||
| Trial 3 | ||
| Trial 4 | ||
| Average speed: | ||
Next change into your clothes. Make sure they fit well and don't slip down when swimming. If you swim with your buddies, make sure you all wear similar clothes to get useful results. Remind your volunteer to record all data in your lab notebook.
| Swim Fully Clothed | ||
|---|---|---|
| Trials | Swim Time | Speed |
| Trial 1 | ||
| Trial 2 | ||
| Trial 3 | ||
| Trial 4 | ||
| Average speed: | ||
Analysis
Calculate the speed of your swims by dividing the distance you swam by how long it took to swim the distance.
Speed = Distance / Time
Plot the data on a scatter plot. Label the X-axis "Clothing" and the Y-axis Speed. Do you see a difference in the speeds?
Describe how the water interacted with your clothes and how drag affected your swim times and speeds. If there was a change in speed, calculate the percentage change in speed:
(Average speed with swimsuit) - (Average speed with clothes)
(Average speed with swimsuit) x 100
(Average speed with swimsuit) x 100
Share your results with your swim buddies and formulate a training plan to get fit.
Variations
Exertion
Does drag affect how easily you tire? Swim 25 meters and calculate the percent change in speed between swimming with a swimsuit and swimming with clothes. How does this compare with the percentage change in speed when swimming 50 meters? Will it make a bigger difference when you swim 100 or 400 meters? What is the effect of exhaustion over such distances?
Flippers
Does the swim time improve if you try to mimic a fish as much as possible? Wear flippers and swim gloves and redo the project.
You may find that as your flippers give you more power, the drag resistance of the clothes will increase a lot with speed. Compare swimming in a swimsuit and swimming with clothes.
Experiment with drag and body position. For the first body position, kick with your head down and arms stretched above your head, palms together. How long does it take to swim 25 meters?
For the second body position, swim holding your arms level with your shoulders.
Is there a difference in swim time between the two body positions?
