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Drag in fluid dynamics
Drag is an important concept in fluid dynamics, and is defined as the fluid resistance that acts on a solid according to the direction of that the fluids is travelling. Drag can be presented in a physics formula as: (Quintela)
Where:
FD= force of drag (force that acts in the same direction of the fluid velocity
p= mass density of water
u=velocity of the object (ex. arms, kicks etc.)
A= area of swimmers' body (ex. hands, feet)
CD= drag coefficient (constant) to represent resistance of object in water (Quintela)
FD= force of drag (force that acts in the same direction of the fluid velocity
p= mass density of water
u=velocity of the object (ex. arms, kicks etc.)
A= area of swimmers' body (ex. hands, feet)
CD= drag coefficient (constant) to represent resistance of object in water (Quintela)
Types of drag
"Form drag- caused by the shape and position of the swimmer"
- "Skin friction drag- caused by friction between water and the swimmer"
- "Wave drag- caused by the formation of waves"
- "Spray drag- caused by the formation of spray (turbulence while kicking)"
- "Interference drag- caused by two body parts being close to each other"
- "Parasitic drag- equal to total drag - induced drag"
- "Pressure drag- equal to total drag - skin fraction drag" (Quintela)
Streamlining to minimize drag
Streamlining your body is crucial in order to minimize the amount of drag you experience as much as possible. Since water is 1000 times more resistant than air, swimmers spend majority of their energy in overcoming drag instead of propulsion. It is important to minimize your surface area as much as posssible when you are swimming. This position is referred to as "streamline" and many professional swimmers spend years trying to master this technique. The streamline position consists of the swimmer moving underneath the water while utilizing the dolphin kick (propulsive kick where the hip initiates the motion) rather than swimming at the top. The swimmers eliminates the water tension that he/she could potentially face while swimming at the surface. (Hensley) Cyclists face very similar circumstances. In order to minimize wind resistance, cyclists lean forward and tuck their arms in in a streamline position in order to minimize their surface area. It is important that when you are assuming the streamline position that you have your head tucked between your biceps with your hands extended, rather than with your head poking up at the surface of the water. The importance of the streamline position connects with Newton's first law of motion: inertia. Unlike travelling through air, the water resistance brings us to a quick stop and eliminates the momentum that we have built up previously to assist us to keep swimming through the water. Recall riding a bicycle. We often don't even pedal as long as we have built a momentum that keep us going. However, this situation is very different to swimming. (Woodford)
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By assuming a streamline position, you are minimizing the drag that would have been produced otherwise. By failing to complete such tips, the swimmer then increases the drag force, therefore slowing them down. The equation of resistance can be represented in the following: (Hensley)
R = 1/2(DPA)v^2
R = 1/2(DPA)v^2
Where:
R: Resistance
D: viscosity of water (constant)
P: Density of water
A: surface area
V: velocity (Hensley)
R: Resistance
D: viscosity of water (constant)
P: Density of water
A: surface area
V: velocity (Hensley)
Symmetry
Symmetry also contributes to the efficiency of a swimmer. You must ensure that your body and its motion are aligned; otherwise, the body will begin to move towards the greater force, therefore making an inefficient stroke. In order to be an effective swimmer, you must balance the body, the forces exerted by the water and the forces that your body itself produces. Imagine a line passing through your head and ending between your legs. Your arms, or any part of your body, should not cross that line. If you break this line of symmetry, your arms now have to work against the forces produced by your body, which slows you done since it`s requiring more energy. Allow your left arm to enter the water in a 10 o'clock position, and your right 2 o'clock position. Not only will this allow you to avoid crossing the boundary line, but also allows your shoulders to rotate forward to grab as much water in front of you and to eventually push that water behind as far as you can to create the greatest amount of propulsion. Also, make sure you try to have a sense of rhythm. This will allow you to expend less energy to travel the same distance. (Physics of Swimming)
Swimming efficiently
Swimming is an aerobic, vigorous exercise that primarily energizes your heart and lungs. Swimming longer distances efficiently and using less energy with freestyle can be achieved by getting a much greater forward propulsion by extending your arm and dragging your arm back as far as you can. Another technique to keep in mind is to have cupped arms and utilizing the bent-arm pull. With prolonging your stroke with a proper follow through, you are applying the pulling force that causes your to go forward and therefore causing each stroke to count for more. This ties in with Newton's second law: (Woodford)
force = mass x acceleration
Recall this how acceleration = velocity/time ? Transform the above formula into this
F= mv/t
Force is also equal to the rate of change in momentum, since p(momentum)=mv
By rearranging the formula, this equation can also be derived: force x time = mass x velocity (Ft = mv)
In order to produce the greatest change of momentum with each stroke, swimmers should apply a force by pulling back on the water for as long as they can and also keeping in mind their swimming form. Our bodies act like machines to get us through the water: our limbs function as levers, which are pivoted at our joints. It is important to remember that when you are swimming freestyle, you can achieve a longer distance with each stroke by reaching forward and by having a good follow-up. By reaching forward and pulling your arm backward as far as you can, you are in turn getting more leverage in the water and you are applying a force longer by pulling backward, which then makes you go forward for a longer distance. This decelerates your limbs exponentially slower, and by reducing the acceleration (the rate of switching arms), you are reducing the force that they are under and therefore reducing the probability of pulling your muscles and other injuries. (Woodford)
Another aspect of physics that contributes to one's swimming speed is the conservation of momentum. The momentum which you place upon your body is the same momentum that you are giving to the water in the opposite direction. By remembering to cup your hands and use your forearm as a paddle to pull your arm back as far as you can allows you to become more of an effective swimmer. (Woodford)
Useful thought: what characteristics exactly does salt water have that makes it much more difficult compared to pool water? Its turbulence and our bodies' compatibility with salt water are a few. Our bodies don't "slice" through the water as easily as it does through pool water. Its greater density and viscosity makes it much more difficult for us. The cold climate causes the salt water to be more viscous. Therefore, because all of these qualities, the body is working much harder and getting more exercise as a result. (Woodford)
force = mass x acceleration
Recall this how acceleration = velocity/time ? Transform the above formula into this
F= mv/t
Force is also equal to the rate of change in momentum, since p(momentum)=mv
By rearranging the formula, this equation can also be derived: force x time = mass x velocity (Ft = mv)
In order to produce the greatest change of momentum with each stroke, swimmers should apply a force by pulling back on the water for as long as they can and also keeping in mind their swimming form. Our bodies act like machines to get us through the water: our limbs function as levers, which are pivoted at our joints. It is important to remember that when you are swimming freestyle, you can achieve a longer distance with each stroke by reaching forward and by having a good follow-up. By reaching forward and pulling your arm backward as far as you can, you are in turn getting more leverage in the water and you are applying a force longer by pulling backward, which then makes you go forward for a longer distance. This decelerates your limbs exponentially slower, and by reducing the acceleration (the rate of switching arms), you are reducing the force that they are under and therefore reducing the probability of pulling your muscles and other injuries. (Woodford)
Another aspect of physics that contributes to one's swimming speed is the conservation of momentum. The momentum which you place upon your body is the same momentum that you are giving to the water in the opposite direction. By remembering to cup your hands and use your forearm as a paddle to pull your arm back as far as you can allows you to become more of an effective swimmer. (Woodford)
Useful thought: what characteristics exactly does salt water have that makes it much more difficult compared to pool water? Its turbulence and our bodies' compatibility with salt water are a few. Our bodies don't "slice" through the water as easily as it does through pool water. Its greater density and viscosity makes it much more difficult for us. The cold climate causes the salt water to be more viscous. Therefore, because all of these qualities, the body is working much harder and getting more exercise as a result. (Woodford)