In definition, terminal velocity describes the velocity a free falling object, which is an object that is not subject to air resistance, reach, but reaching a terminal velocity means when the resistance of the medium (could be air resistance) equals to the weight of the object, so in this case, air resistance does exist in the system, which is contradictory to the situation a free falling object should experience. So does air resistance exist or not? This is causing confusion for me. I wonder which part of my understanding of the terminal velocity is wrong.
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2$\begingroup$ "In definition, terminal velocity describes the velocity a free falling object" Where have you seen this definition? This is not correct. You are right that terminal velocity is a term that only has meaning when a resistance is present such as air drag. $\endgroup$– SteevenCommented Apr 24, 2021 at 15:18
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$\begingroup$ "In definition, terminal velocity describes the velocity a free falling object" When you make statements like that that end up being contradictory, it's helpful to provide a source. What is your source? $\endgroup$– Bill NCommented Apr 24, 2021 at 15:38
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$\begingroup$ It's the definition provided by the oxford language dictionary: "the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration", the first thing that came up when I did the google search. $\endgroup$– gggjackieCommented Apr 25, 2021 at 18:02
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$\begingroup$ Also on Britannica, it says terminal velocity is the steady speed achieved by an object freely falling through a gas or liquid. britannica.com/science/terminal-velocity $\endgroup$– gggjackieCommented Apr 25, 2021 at 18:10
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4 Answers
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In definition, terminal velocity describes the velocity a free falling object, which is an object that is not subject to air resistance, reach . . . . is not true.
. . . . reaching a terminal velocity means when the resistance of the medium(could be air resistance) equals to the weight of the object is true.
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$\begingroup$ So, is the definition provided by the oxford language dictionary wrong? The definition: the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration. Or is my understanding wrong? $\endgroup$ Commented Apr 25, 2021 at 18:04
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$\begingroup$ The Oxford dictionary definition is entirely consistent with your statement which I stated was true. $\endgroup$– FarcherCommented Apr 25, 2021 at 20:00
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In definition, terminal velocity describes the velocity a free falling object
Where have you seen this definition? This is not correct.
You are correct in saying that the term terminal velocity only has meaning when a resistance (such as drag forces) is present. Otherwise you would never stop accelerating and would thus never reach any terminal speed.
The derivation of terminal velocity in air also does include air resistance and the properties of the air.
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$\begingroup$ Hi, I saw it in the Oxford language dictionary: the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration. Is this definition wrong or is my understanding wrong? $\endgroup$ Commented Apr 25, 2021 at 18:06
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$\begingroup$ @gggjackie I see. I guess this dictionary isn't using a scientifically strict definition of freely falling. Your understanding is not wrong just keep air resistance regardless of this use of this being called a free fall. $\endgroup$– SteevenCommented Apr 25, 2021 at 19:16
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$\begingroup$ Oh, what do you think they are referring to when saying freely falling then? $\endgroup$ Commented Apr 26, 2021 at 16:29
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$\begingroup$ @gggjackie Well, they just mean falling, I'm sure. Falling without obstacles or help or hinder but with air resistance. Just like how you would casually define a free fall if you were skydiving without a parachute. $\endgroup$– SteevenCommented Apr 26, 2021 at 19:39
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Which is an object that is not subject to air resistance
Wrong , terminal velocity is actually determined only in the cases when ther IS air resistance or else in case of vacuum the velocity will just keep on increasing and the terminal velocity will be infinite ( that is the case of a free fall)
Considering real situations where air drag is actually present we know the forces in the y direction will be
F (y) = Fdrag - Fgravity
Ma(y) = 1/2 Cd* density *Cross sectional Area * V ^2 - Mg
so now we know that the body will reach its terminal velocity when Force of drag is equal to Mg i.e. a = 0
thats how you get the above formulae for terminal velocity
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At terminal velocity, magnitude of air resistance equals weight which means net force acting on the body equals zero. As soon as terminal velocity is reached during free fall, speed will not change. Also note that the resistance force is directly proportional to the speed of the object.
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$\begingroup$ But doesn't free fall mean there is no air resistance in the scenario? $\endgroup$ Commented Apr 25, 2021 at 18:19