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examples of air resistance force

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From Encyclopedia

resistance

re·sist·ance / riˈzistəns/ • n. 1. the refusal to accept or comply with something; the attempt to prevent something by action or argument: she put up no resistance to being led away. ∎  armed or violent opposition: government forces were unable to crush guerrilla-style resistance. ∎  (also re·sist·ance move·ment) [in sing.] a secret organization resisting authority, esp. in an occupied country. ∎  (the Resistance) the underground movement formed in France during World War II to fight the German occupying forces and the Vichy government. Also called maquis. ∎  the impeding, slowing, or stopping effect exerted by one material thing on another: air resistance would need to be reduced by streamlining. 2. the ability not to be affected by something, esp. adversely: some of us have a lower resistance to cold than others. ∎  Med.& Biol. lack of sensitivity to a drug, insecticide, etc., esp. as a result of continued exposure or genetic change. 3. the degree to which a substance or device opposes the passage of an electric current, causing energy dissipation. Ohm's law resistance (measured in ohms) is equal to the voltage divided by the current. ∎  a resistor or other circuit component that opposes the passage of an electric current. PHRASES: the line (or path) of least resistance an option avoiding difficulty or unpleasantness; the easiest course of action.


From Yahoo Answers

Question:Was studying MCAT Physics and came across concept of equillibrium of forces. Namely gravity. Okay, if a parachuter is falling and doesn't open his shoot, the system then has acceleration because the downward force of gravity is greater than the upoward force. However, if he opens his shoot, supposedly the chute's air resistance is equal to the downward force of gravity? I don't understand how that suddenly makes the system have equillibrium (and does that mean "no acceleration)? I mean if he opened a mini tiny umbrella there would be more air resistance but not equillibrium. Also if he opened a parachute 10 times larger than a normal parachute he would have much more equillibrium and less acceleration...so what causes opening the chute suddenly to be related to zero accerlation? I understand that air resistance slows a falling body down; I just don't understand the shift from non-equillibrium to equillibrium.

Answers:You always reach equilibrium with a falling body in air. Parachute or no parachute. Air resistance increases with speed. So the falling body accelerates downwards, with the speed increasing until the increasing force of air resistance equals the downwards force of gravity. At that point the body is in equilibrium and acceleration stops. Of course this stabile point changes. as you move your arms out, for example, that increases air resistance, so momentarily you have a net upwards force, and your speed decreases until you reach equilibrium again. Same thing happens when you open the parachute. Air resistance increases, and the net force is upwards, so you slow down until you reach equilibrium again, at a much slower speed. Bottom line, if you have enough time, you always reach an equilibrium point falling. It may be too fast to survive hitting the ground, so you open the parachute and get to a different equilibrium point that is slow enough to survive hitting the ground. Hope that is clear. You can email me if not. .

Question:hey...can someone give me examples of air resistance!

Answers:In fluid dynamics, drag (sometimes called air resistance or fluid resistance) refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity. Unlike other resistive forces such as dry friction, which is nearly independent of velocity, drag forces depend on velocity. For a solid object moving through a fluid, the drag is the component of the net aerodynamic or hydrodynamic force acting opposite to the direction of the movement. The component perpendicular to this direction is considered lift. Therefore drag opposes the motion of the object, and in a powered vehicle it is overcome by thrust. In astrodynamics, and depending on the situation, atmospheric drag can be regarded as an inefficiency requiring expense of additional energy during launch of the space object or as a bonus simplifying return from orbit. Ron

Question:I need help working out the air resistance formula... I've been on wikipedia and they state on but that asks for the drag coefficient and I couldn't understand it. So lets say I have a solid copper square. And it was just dropping via gravity (Assume 9.81) how would I work out the air resistance on it? Please explain in as much detail as possible (I'll need it!) Thank you very much...

Answers:The drag coefficient only applies to specific shapes. In this case you need the size and thickness too, but it would not be a streamlined shape or oriented in a particular way. Probably it would fall in an indeterminate way, spinning or fluttering. The air flow would be disrupted, or turbulent, or chaotic in motion so not readily predicted or calculated. The best you can hope for with turbulent motion is an "average". I think the best approach would be experimental. There is a terminal speed, meaning an object falling in air will accelerate to some speed where the drag balances out the force of gravity on average. If you can determine the terminal speed then the force equals gravity at that speed. Possibly the terminal speed itself will be all you want to know. You could time the drop from different heights, but there are practical issues there. It may fall a long way before a terminal speed is achieved. I suspect it could take 20 or more seconds of falling to settle to a terminal speed. This implies dropped from an airplane. Hmmm. The terminal velocity can be calculated if the drag coefficient is known (see link) but in this case it is not known. I mean it may be unstable. It can be made stable and perhaps known from a list or book by an appropriate shape and weight distribution - consider an aerial bomb or a ball or a rocket, as compared to a sheet of plywood (flat or vertical?) or a leaf. The article does mention that a 0.30 caliber bullet falls at about 360km/h. I think this may be tumbling, but it is small and heavy. There is an example for a sphere, which might be useful, as this is definitely a constant drag - its orientation doesn't matter.. The second link has a calculator for cases where the drag coefficient is known and stable. Note that all this falls apart once the speed of sound is approached, where a new drag coefficient is needed that takes into account compressibility (shock wave) effects. . The third link has a bit about how drag coefficient is determined (experimentally) for a "stable" body like an airplane.

Question:True or false. when air resistance does not affect the motion of a projectile, its horizontal and vertical components of velocity remain constant. Yes or no. Does the force of gravity change the speed of a satellite in a circular orbit?

Answers:True...sort of! The force of gravity applies an exponential acceleration on any mass. With no outside influences the components of velocity would be constant. An object would steadily accelerate in a downward motion or decelerate in an upward one. But you must consider ALL outside influences (although minimal and virtually insignificant) and not just air resistance. No! Gravity is constantly pulling the satellite to earth, but the force is countered by the centripetal force of the orbit. As the satellite encounters resistance to slow it down (space debris, atmosphere, radiation), its orbit will degrade and it will be pulled towards the earth...but it will not be gravity that slows the rotation. Gravity will simply move it closer as the speed reduces.

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P036 Forces - Air resistance on a bike :Physics - forces air resistance