Why is my rebound height not following the expected trendline?

In summary: No, the center of mass does not change. Adding mass to either end does not change the equation for the center of mass. Adding mass to the center does not change the equation for the center of mass.
  • #1
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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  • #2
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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  • #3
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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  • #4
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
__________________
moo (moo') adj. Of no practical importance; irrelevant, such as a moo point (i.e. a cow's opinion).
 
  • #5
Thanks moo .. really appreciated
 
  • #6
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).
 
  • #7
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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1. What is spin and how does it affect the rebound height of an object?

Spin refers to the rotational motion of an object. When an object is spinning, it creates a lifting force known as the Magnus effect, which can increase or decrease the rebound height depending on the direction of the spin.

2. How is the spin of an object related to its rebound height?

The spin of an object is directly related to its rebound height. The more spin an object has, the higher the rebound height will be due to the Magnus effect. Similarly, less spin will result in a lower rebound height.

3. Can the rebound height of an object be controlled by changing its spin rate?

Yes, the rebound height of an object can be controlled by changing its spin rate. By increasing or decreasing the spin rate, the lift force created by the Magnus effect can be altered, resulting in a higher or lower rebound height, respectively.

4. Is there a limit to how much spin can affect the rebound height of an object?

Yes, there is a limit to how much spin can affect the rebound height of an object. This is known as the critical spin rate. Beyond this point, increasing the spin rate will not result in a higher rebound height as the Magnus effect reaches its maximum lift force.

5. Does the surface or material of an object affect its spin and rebound height?

Yes, the surface and material of an object can affect its spin and rebound height. Rougher surfaces or materials with more friction can reduce the spin rate and therefore decrease the rebound height. Smooth surfaces or materials with less friction can allow for a higher spin rate and result in a higher rebound height.

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