Why is my rebound height not following the expected trendline?

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Discussion Overview

The discussion revolves around an experiment involving two balls of different masses dropped from a fixed height, focusing on how the mass of a smaller ball affects its rebound height. Participants explore the implications of added mass, aerodynamics, and rotational dynamics on the observed rebound heights, which deviate from an expected elastic model trendline.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the crude method of adding mass using tape may have altered the ball's aerodynamics, leading to increased spin and a lower rebound height than expected.
  • Another participant agrees that unbalanced balls can exhibit a "wonky" bounce due to lopsided impacts, which absorb energy and result in a partially horizontal bounce.
  • Questions are raised about how unbalanced weights affect the ball's rotation and whether adding weights changes the moment of inertia, potentially altering spin.
  • One participant explains that during impact, the heavier side of the ball continues moving, causing it to pivot and rotate, which may affect the rebound height.
  • Further inquiries are made about the relationship between added mass, center of mass, and moment of inertia, particularly in relation to the ball's spin.

Areas of Agreement / Disagreement

Participants generally agree on the effects of unbalanced weights on the ball's bounce and rotation, but there are ongoing questions and uncertainties regarding the specific mechanics involved, such as the impact on moment of inertia and the center of mass.

Contextual Notes

Participants express uncertainty about the exact contributions of aerodynamics and rotational dynamics to the observed results, and there are unresolved questions about the mathematical relationships governing these phenomena.

Who May Find This Useful

This discussion may be of interest to those studying experimental physics, mechanics, or anyone exploring the effects of mass distribution on motion and energy transfer in physical systems.

GreenSabbath
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My Experiment consists of two balls of different masses falling together in the y-axis from the same fixed height.Im researching how mass of the smaller ball affects its rebound height. My method of adding mass however was very crude as I stuck weights on using tape. This surely altered the aerodynamics of the ball and I did notice an increased spin on the ball, (unbalanced weight arrangeent?). What does this mean? The energy given by the larger ball is used up in giving spin and velocity to the samleer ball hence the rebound height is lower than what it hypothetically should have been?
My readings are very far off the elastic model i formulated, barely even following the trendline. How do i explain this?
 
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I think your observations are correct. :wink:

Unbalanced balls have an extremely "wonky" bounce. The lopsided impact causes rotation which absorbs much of the energy normally used in the rebound, plus the spin gives it a partially horizontal bounce rather than all vertical (which trades some height for distance).

If you want anything resembling accurate results, I'd say get more balls... :biggrin:

moo
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moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
 
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What causes this "wonky" bounce, alteration in a ball's aerodynamics?
How can I explain it assuming let's say I add 200 grams on the two opposite ends of a ball (x axis) but they arnt exactly aligned ... will the ball rotate around the y axis? Adding weights causes the spin because area of the body is proportional to air drift?
And why did the spin increase as heavier weights were placed onto the ball?
Does adding weights change the moment of inertia which ends up altering spin?
 
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When the ball impacts, the heavy side doesn't "stop" when the lighter side does, so the ball pivots a bit, and this continued movement by the heavier side translates into rotation.

If the ball is dropped from a good height then surface aerodynamics will also come into play, but I doubt it's a factor from a few feet unless you really have a large surface difference.

moo
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moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
 
Thanks moo .. really appreciated
 
You're welcome. :wink:

Btw, "wonky" is not a technical term... :biggrin:

moo
__________________
moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
 
Would the center of mass change?
What about moment of inertia ?
How can I link the increase in the added mass to the spin of the ball?

For a full sphere, I = 2/5 m r2
By adding two bulk wieight on either side am i changing the value for alpha?
 
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