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Drag Experiment

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

We investigate the effects of drag resistance. We compare the time it takes to swim 25 meters in a swimsuit versus swimming the same distance in fully clothed to discover how each affects swim times.

Find a swimming pool that is at least 25 meters in length during a time when it is not crowded. Do not perform this experiment if you are not in good health.

So warm up, suit up, and get ready to dive in!

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. The fluid can be a liquid or a gas. Drag is also the resistance to the motion of a solid body through a fluid. Engineers who design cars and airplanes always test their designs to see how drag affects the 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.

Materials and Equipment

Make sure to take all your materials with you when you go for your swim trials.

  1. Stopwatch
  2. Lab notebook
  3. Swimsuit, close-fitting
  4. T-shirt and shorts
  5. Jogging suit or tracksuit or jeans and hoodie
  6. 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 measurable times.

Note: Rest at least 10 minutes between trials! Remember to swim as fast as you can. Improve your swim times by picturing a shark swimming behind you!

Start your Swim Test

Have a friend time how long it takes you to swim 25 meters and record the data in tables like the ones shown below. Swim several lengths to get a good average.

First test your speed in your swimsuit or T-shirt and shorts. Perform some warm-up exercises before starting the swim.

Swimming in Swimwear
TrialsSwim Time (seconds)Speed
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Average speed:

Relax until you get back to resting pulse. Then change into a full set of 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 friend to record all data in your notebook.

Swimming Fully Clothed
TrialsSwim Time (seconds)Speed
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
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 sports clothes. Describe 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

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 repeat the project above. Fin training helps make you a more effective swimmer and strengthens your core.

This may sound easy, but is not when you're fully clothed. The fins give you a strong push, the clothes slow you down. Your legs feel the difference when they work hard.

While 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.

Small fins need less effort to use than longer fins, but don't give as much of a push. The longer the fin, the more work you have to do to balance the additional weight of the fin. Point your toes, do not bend too much at the knees.

Experiment with drag and body position. Practice swimming on your back and front.

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?