Calculating Gravity from Inclined plane

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SUMMARY

The discussion focuses on calculating gravitational acceleration (g) using an inclined plane and a rolling ball. The participants utilize the equation g = a / (sinθ / (1 + I/mr²)), where sinθ is derived from the ramp's height and length. Initial calculations yield values significantly lower than the expected 9.8 m/s², prompting further exploration of the effects of the ball's moment of inertia. The conversation emphasizes the importance of understanding the relationship between linear and rotational motion in this context.

PREREQUISITES
  • Understanding of kinematics, specifically the equation d = 1/2at².
  • Familiarity with the concept of moment of inertia, particularly for a solid sphere (I = 2/5mr²).
  • Knowledge of the parallel axis theorem and its application in rotational dynamics.
  • Basic proficiency in using Excel for data analysis and graphing.
NEXT STEPS
  • Study the derivation of the equation g = a / (sinθ / (1 + I/mr²) for inclined planes.
  • Learn about the relationship between linear velocity and angular velocity in rolling motion.
  • Explore the concept of effective mass in rotational dynamics and its implications in calculations.
  • Investigate the effects of different shapes and masses on the moment of inertia and acceleration down an incline.
USEFUL FOR

Students of physics, particularly those studying mechanics, as well as educators and anyone interested in the dynamics of rolling objects on inclined planes.

  • #31
Fat_Squirrel said:
Which means our ratio should be 1 / (2/5 r^2/x^2 + 1) ??
Almost.
I'm afraid I may have confused you a little.
When dealing with bodies that are both rotating and moving linearly, there are two main ways of thinking of it:
- as a linear movement of the mass centre, plus a rotation about the mass centre, or
- as a rotation about the instantaneous centre of rotation.
With the first approach, the total KE is ##\frac 12 m(v^2+\frac 25 r^2\omega^2) = \frac m2 (x^2+\frac 25 r^2)\omega^2##, exactly the result the second approach gives.
Hence the fraction of the total KE that is linear is ##\frac{x^2}{x^2+\frac 25 r^2}##.
Can you see how to get from there to an expression for v as a function of the height loss?
 
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  • #32
1/[x^2 / (x^2 + 2/5 r^2)] * a * sinθ

so 1/[10.41^2 / (10.41^2 + 2/5 * 15^2) * 0.1646 * (0.061/2)] = 9.866

Answer looks good,how'd I go with this one?
 
  • #33
Fat_Squirrel said:
1/[x^2 / (x^2 + 2/5 r^2)] * a * sinθ

so 1/[10.41^2 / (10.41^2 + 2/5 * 15^2) * 0.1646 * (0.061/2)] = 9.866

Answer looks good,how'd I go with this one?
Yes, I believe that works.
 
  • #34
haruspex said:
Yes, I believe that works.

Once again, thanks for your help and patience. Will let you know if we got the answer my teacher expected.
 
  • #35
haruspex said:
Yes, I believe that works.

here's the solution they provided - https://youtu.be/IED3ujslfPY. I got a slightly different answer because I calculated acceleration differently.
I used values associated with t^2 and ran least squares on them to get my value for the slope, he used √d values - i thought they'd give same answer, but slightly different it seems.

Anyway if I use his value for acceleration I get the exact same answer he does. Thankfully my answer was within the margin of error. Thanks again.
 

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