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### 15 Cards in this Set

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• Back
 BUOYANT FORCE - A force exerted on an object immerged in a fluid - Always acts vertically - Acts upward on an object that is immersed in fluid - Absolute force- weight of water the object displaces - The size = weight of the volume of fluid displaced by the object DYNAMIC FORCE - The force of an object in a fluid environment due to its relative motion in the fluid - drag and lift forces - relative motion- runner against wind - 2 objects similar in size and shape will experience the same dynamic fluid forces, but the more massive object will experience less acceleration. PRESSURE - due to the weight (force) of the water above you - water pressure acts in all directions with the same magnitude at the same level - the deeper you go the deeper the pressure - force per unit area SPECIFIC GRAVITY - ratio of the weight of an object to the weight of an equal volume of water. - anything with a specific gravity of 1 of less will float DENSITY - mass/volume - A person will float when air is in their body cavities, but when they have a forced exhalation even a very lean person will sink FLUID FORCE - proportional to fluid density, surface area of an object, relative velocity of the object with respect to the fluid (squared). - Fluid forces are exerted on the object by the fluid. DRAG FORCE - component of the resultant dynamic fluid force that acts in opposition to the relative motion of the object with respect to the fluid - Slows down relative velocity of an object if it is the only force acting on it - proportional to the accleration of fluid molecules and the mass of the molecules SURFACE DRAG - friction forces acting between the fluid molecules and the surface of the object - clothing worn on athletes is smooth to reduce surface drag. The rougher the surface the more friction. FORM DRAG - sum of the impact forces resulting from the collisions between the fluid molecules and the object. - shape drag, profile drag, shape drag - The larger the change in direction the larger the force exerted - increases as the amount of turbulent form increases - athletes put body parts in an elongated orientation relative to the fluid flow to reduce form drag. LAMINAR FLOW - layers of fluid which are smooth air particles parallel to each other - molecules are close to surface of object - If a discus is thrown against the wind it will create a greater laminar force. TURBULENT FLOW - Layers of fluid which aren't smooth and aren't parallel - fluid molecules don't press against surface because the fluid molecules aren't large enough to be deflected back. - The fuzz on a tennis ball and the dimples on a golf ball reduce form drag by creating a layer of turbulent flow and making laminar flow smoother. This increases speed and distance - In baseball the spin of the position of a pitchers hand on the stitches determines which way the ball turns. The seams cause turbulent flow LIFT FORCE - the dynamic fluid force component - acts perpendicular to the relative motion of the object - changes direction of relative motion of the object - directed in any direction not just upward. - A discus should be as perpendicular to the ground as possible so it will increase the vertical lift force. It will stay in the air longer. BERNOULLI'S PRINCIPLE - faster moving fluids exert less pressure laterally than do slower moving fluids - objects can have lift force if their longest dimension is aligned with flow to produce laminar flow - An airplane wing is lifted when the molecules around the curved area on top move faster than the air molecules along the flat surface on the bottom. By the top molecules moving faster less pressure is created so a lift force can occur. - MAGNUS EFFECT - a lift force caused by a spin - Lift force acts downward on the ball. The top of the ball has a forward velocity while the bottom of the ball has a backward velocity. The air molecules have a backward velocity. The air molecules move faster at the bottom than on the top because they go in the same direction as the air. The lower pressure on the bottom creates the lift force. CENTER OF PRESSURE - point of application of the force to the object - If the resultant force acting at the center of pressure is not on a line passing throught the center of gravity, a torque is produced tha causes the object to rotate.