Calculating air resistance homework

• mindboggling
In summary: The centripetal force is always constant, so it would always be the same. The hanging weight depends on the radius of the bung, so it would change depending on the radius.

Homework Statement

I'm currently working on a lab which involves swinging a bung in the horizontal plane (just like a conical pendulum), however I'm a bit stumped at finding air resistance.

The variables we know are the radius, the centripetal force and the velocity of the bung.

The Attempt at a Solution

In attempt to calculate the wind resistance, i did the following:

W (non conservative) = delta KE +delta PE

Force (of air resistance) x distance = KE (theoretical) - KE (Experimental)

If i plotted KE theoretical and KE experimental on the y-axis and radius on the x, there is a gap inbetween both series, a gap that gets wider as velocity increases. This makes sense because velocity is proportional to force. And here i yield difference of 0.5 to 0.7.

HOWEVER, according to: Force (of air resistance) x distance = KE (theoretical) - KE (Experimental)

if i divide both sides by distance (2 pi radius: the conical pendulumn travles in a circle) and when i plot the force of air resistance over radius, air ressistance seems to go down as r increased! but this can't be the case because for some constant centripetal force, r is proportional to velocity SQUARED, and velocity is proportional to the force of air resistance.

So what did i do wrong??

thanks

Welcome to PF mindboggling.

Do your calculations indicate that the centripetal force is too large (for the given speed and radius)?

How did you determine the magnitude of this force (weight hanging from the sting in the center)?

Last edited:
centripetal force is always constant. The independent variable would be the radius, because in this lab we are trying to see how radius affects the speed for a given centripetal force.

Yes, the magnitude of centripetal force is provided the weight hanging from the string in the center

Anyone?

Many thanks

What I meant is that if you had the mass (of the bung) you could calculate it (the centipetal force) and compare it with the hanging weight. How do these two forces compare?

Last edited:

1. What is air resistance?

Air resistance is the force that opposes the motion of an object through the air. It is caused by the collision of air molecules with the surface of the object.

2. How is air resistance calculated?

Air resistance is calculated by using the formula F = 1/2 * p * v^2 * A * C, where F is the force of air resistance, p is the density of air, v is the velocity of the object, A is the cross-sectional area, and C is the drag coefficient.

3. What factors affect air resistance?

The factors that affect air resistance include the speed and size of the object, the density of the air, the shape and surface area of the object, and the viscosity of the air.

4. How does air resistance affect motion?

Air resistance can slow down the motion of an object by exerting a force in the opposite direction. This can be seen in activities such as skydiving or driving a car, where the force of air resistance must be overcome to maintain a constant speed.

5. How can air resistance be reduced?

Air resistance can be reduced by making the object more streamlined, decreasing its surface area, or increasing its velocity. Other methods include using materials with lower drag coefficients or manipulating the surrounding air to reduce its density or viscosity.

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