Air Resistance (1 Viewer)

[scardizzle]

My School's prac trial is coming up and I was wandering if air resistance is a valid response for why your experimental value is different from your theoretical value for motion type practicals e.g. determining a value for g using a pendulum because i remember one time i was marked incorrect for putting air resistance as a response.

 

[Al-Ghazali]

Errors - parallax error, Variations in mass such as presence of ore bodies, oils, gas feilds may have affected the value of G, reaction time error if you used a stopwatch

 

[scardizzle]

but isnt air resistance an error in the system?

 

[clintmyster]

but isnt air resistance an error in the system?

it is but just don't go describing it as an "experimental error" because that is due to friction of the string with the wire, clamp and retort stand frailty, not a perfect pendulum formed, weakening string and so forth.

 

[scardizzle]

it is but just don't go describing it as an "experimental error" because that is due to friction of the string with the wire, clamp and retort stand frailty, not a perfect pendulum formed, weakening string and so forth.

But isn't friction similar to air resistance? Since they are both forces that oppose the movement of the pendulum?

 

[cutemouse]

No air resistance doesn't affect the experiment, at HSC level, as the period isn't affected (much).

 

[darkchild69]

Well, yes it has an effect. Of course it does.

With the HSC syllabus, they are using the "simple gravity pendulum" which actually assumes no air resistance and friction.

I would say that air resistance definately is a valid response, but seeing as this can be said for just about every single prac you do, EVER. Perhaps your teacher would rather you try and identify something else?

 

[annabackwards]

As everyone says, air resistance is assumed to be zero at the HSC physics level - mention other things.

 

[pman]

and don't call the reaction time human error, although it is, our entire grade called it that and got a ten minute lecture about humans never making mistakes! (seems kinda stupid I know)

 

[shady145]

if ur concerned about air resistance just say u added extra mass to give it more momentum, decreasing air resistance

 

[scardizzle]

okay got it, thanks for all the help guys

 

[study-freak]

if ur concerned about air resistance just say u added extra mass to give it more momentum, decreasing air resistance

how does adding mass decrease air resistance?
It might decrease the impact of air resistance on pendulum motion though.

 

[Uncle]

You should be more worried about keeping the angle of swing less than 10 degrees.
Because an approximation that sin x = x is used and the tolerance of the error only goes up to 10 degrees and any higher the approximation sin x = x ruins your results.

if ur concerned about air resistance just say u added extra mass to give it more momentum, decreasing air resistance

Fool,
although not in the HSC syllabus drag force is given by:

[maths]F_{D} = C_{D}A\frac{\rho v^{2}}{2}[/maths]
(Cengel and Cimbala, Fluid Mechanics 2nd edition)

and

[maths]\rho[/maths] is the density of the object then:

[maths]\rho = \frac{mass}{Volume}[/maths]

Therefore if air resistance were taken into account, it would be proportional to the mass.
You claim to have come 1st in physics?
What a joke.

 

[cutemouse]

You should be more worried about keeping the angle of swing less than 10 degrees.
Because an approximation that sin x = x is used and the tolerance of the error only goes up to 10 degrees and any higher the approximation sin x = x ruins your results.

I actually thought it was like 4 degrees, but our Physics teacher told us that at HSC level that doesn't matter.

 

[shady145]

It might decrease the impact of air resistance on pendulum motion though.

thats what i meant

 

[shady145]

Therefore if air resistance were taken into account, it would be proportional to the mass.
You claim to have come 1st in physics?
What a joke.

yea i meant the effects of air resistance would be reduced, if we take a simple example, if we swung a pingpong ball as apposed to a solid metal ball, well... u know which one is going to lose more velocity...conservation of momentum
but its not in our course so it doesnt matter

 

[Dumbledore]

Fool,
although not in the HSC syllabus drag force is given by:

[maths]F_{D} = C_{D}A\frac{\rho v^{2}}{2}[/maths]
(Cengel and Cimbala, Fluid Mechanics 2nd edition)

and

[maths]\rho[/maths] is the density of the object then:

[maths]\rho = \frac{mass}{Volume}[/maths]

Therefore if air resistance were taken into account, it would be proportional to the mass.
You claim to have come 1st in physics?
What a joke.

i think that p means the density of the medium the object is travelling through

if it did apply to the object itself, it would say F=ma=km where k is all the other formula stuff
cancelling out a = k? meaning acceleration due to drag is independant of mass?

 

[Uncle]

i think that p means the density of the medium the object is travelling through

if it did apply to the object itself, it would say F=ma=km where k is all the other formula stuff
cancelling out a = k? meaning acceleration due to drag is independant of mass?

You also forgot the drag force F = -cv where c is the drag coefficent which is not included in HSC Physics.
We are doing an actual experiment on Earth with air in the atmosphere there will be air resistance.

 

[darkchild69]

You should be more worried about keeping the angle of swing less than 10 degrees.
Because an approximation that sin x = x is used and the tolerance of the error only goes up to 10 degrees and any higher the approximation sin x = x ruins your results.



Fool,
although not in the HSC syllabus drag force is given by:

[maths]F_{D} = C_{D}A\frac{\rho v^{2}}{2}[/maths]
(Cengel and Cimbala, Fluid Mechanics 2nd edition)

and

[maths]\rho[/maths] is the density of the object then:

[maths]\rho = \frac{mass}{Volume}[/maths]

Therefore if air resistance were taken into account, it would be proportional to the mass.
You claim to have come 1st in physics?
What a joke.

Dude.. think about that equation.. The density is referring to the density of the medium which the object is travelling through..

So, really.. Drag force is independent of mass of the object itself.

BUT

If that is so..

Then all objects the same "shape" so to speak would experience the same "drag force"

And remember by Newtons 2nd Law.. If objects experience the same force, the object with the lower mass will experience the a higher "acceleration"

So, although drag force is independent of mass, the acceleration of the object is inversely proportional to the mass.

And as shady said, the object with the lower mass will be more greatly influenced by the drag force due to N2L



Please don't talk shit to others if you're one of those who think they are king shit but use wikipedia to get all their info..

 

[Puttah]

Therefore if air resistance were taken into account, it would be proportional to the mass.
You claim to have come 1st in physics?
What a joke.

if ur concerned about air resistance just say u added extra mass to give it more momentum, decreasing air resistance

Maybe it's just me, but even though shady's terminology wasn't quite correct, it's pretty easy to follow what he actually meant.

Uncle, sure, use formulas to back up your statement; but when you can't even apply (and probably misunderstand) the ins and outs of the formula yourself, well...

And whatever happened to using logic every now and then? Kudos to you shady for actually having the guts to do so