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# 6 centre of gravity

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• 1. Centre of Gravity<br />
• 2. Center of Gravity    Gravity is a force which is always present and is a pulling force in the direction of the centre of the earth. This force acts on every body through an imaginary point called the centre of gravity (GG). A solid object like a shot or discus has its CG in the centre and this is a fixed point.    The human body is a complex and constantly changing shape. The centre of gravity now moves according to the positioning of the body and limbs. The CG may be inside the body, for example, when standing or it may be outside the body as in the pole vault and flop high jump bar clearances<br />Centre of Gravity<br />http://www.coachr.org/biomechanics.htm<br />
• 3. Centre of Gravity<br />http://www.coachr.org/biomechanics.htm<br />
• 4. As you float, your weight presses down into the water; the water presses back, pushing you up.<br />When you get into the pool, your body displaces a volume of water (the "hole" in the water that your body fits into). As long as the water your body displaces weighs more than you do, you float.This is basically Archimedes' Law. <br />You weigh less than the water you're in, because your lungs are full of air, like a balloon, and like a balloon, the air in your lungs lifts you to the surface naturally.<br />Buoyancy: What is it?<br />http://www.relaxnswim.com/physics/buoyancy.htm<br />
• 5. Everyone floats in the water at their own natural level<br />Different factors contribute to how high — or low — in the water you float.<br />First, your body type has a lot to do with your buoyancy. Fat floats, as you've probably heard, while your bones and muscles, denser than fat, are not as willing to float.Also, the relative size of your lungs to the rest of your body determines how high in the water your body will float.<br />Second, the density of the water is a factor. Saltier water weighs more per unit of volume, so you will float higher in saltier water (the Red Sea, for instance) than you would in fresh water.<br />Why don’t we float alike?<br />http://www.relaxnswim.com/physics/buoyancy.htm<br />
• 6. Finally, there is a curious phenomenon of apparently greater buoyancy — for some people — in deep water. According to Melon Dash of the Transpersonal Swimming Institute, “Buoyancy and feeling buoyancy are two different things. You can be buoyant but not feel buoyant. Your buoyancy does not change between the shallow and the deep. Your feeling of buoyancy may change.<br />“Feeling  buoyancy in water is all about 'presence' in one's body.Presence — feeling while swimming — is most available when a swimmer is not distracted by the pool bottom, or anything else.<br />http://www.relaxnswim.com/physics/buoyancy.htm<br />
• 7. Why don’t we float alike?<br />“The pool bottom is closer in the shallow end and farther away at the deep end. Because it's so close in the shallow end and you know you can use it any time, it may also be a distraction: some of your awareness, that is, some of your attention or presence is on the bottom.<br />“When this distraction is not there in the deep end due to the fact that we can't use the bottom there, people often feel more buoyant in the deep: their awareness is all at the surface rather than part of their awareness being at the bottom, as in the shallow.”<br />http://www.relaxnswim.com/physics/buoyancy.htm<br />
• 8. Afactor you CAN control is how relaxed you are. Tense muscles often keep your body a bit lower in the water, since many people breathe more shallowly and rapidly when tense (hence less air in the lungs for floating).Did you ever play the “thinking heavy” game as a kid? You'd be harder to pick up if you imagined yourself to be as heavy as a piano, easier to pick up if you pretended to be a balloon.<br />Again, we each have our natural level of buoyancy. And then, there are those few who don't float at all (far fewer than people realize).<br />But no matter how low in the water you float or glide or swim, it has nothing to do with ultimately learning to swim. Period. You'll adjust your stroke, roll your face out a bit more to get your air, and swim.<br />http://www.relaxnswim.com/physics/buoyancy.htm<br />
• 9. A proof of Archimedes' Principle is given by the equal-armed lever balance of special shape, the hydrostatic balance. The body to be weighed hangs below one scale and immerses completely in the fluid, in which its loss of weight is to be found. C is a hollow cylinder, the internal volume of which equals that of the filled cylinder D. You first establish equilibrium of the balance, while D is surrounded by air and C is empty. <br />If you now place the container with the fluid below D, so that it is completely immersed, the balance deflects to the right, that is, D has lost weight. If you now fill C completely with the same fluid as is already in D, equilibrium is restored. The loss of weight is thus compensated by the weight of a volume of fluid, which is equal to the volume in the cylinder D. However, that is the volume of the fluid, which D has displaced by taking its place.<br />Hydrostatic Balance<br />
• 10. The Mr. Smooth program allows you to pause, speed up and slow down the freestyle stroke<br />Mr. Smooth<br />
• 11. Using the Mr. Smooth software program, pause, speed up and slow down the swimmer. <br />Look at the swimmer from different angles to see the ideal freestyle swimming stroke<br />Compare your recorded swimming stroke with that of Mr. Smooth.<br />How do you compare?<br />What is Mr. Smooth doing that you were not?<br />Video Comparison<br />
• 12. Theory: Levers<br />Prac: Competitive Swimming Stroke Development<br />Reminder:<br />Assessment drafts are due beginning of next week!<br />Looking Forward to Next Lesson:<br />