Why Does a Lighter Ball Create a Deeper Crater in Physics Experiments?

[Scollitt]

Hi, I am in my second year at Sixth Form College and I have chosen to do Crater Formation for my second year physics coursework.
I took some readings and found that a lighter ball makes a deeper crater than a ball of the same diameter but greater mass. I don't know why this is. I would expect the heavier ball to make a deeper crater but my results show otherwise.
Can anyone help please?

Steve

 

[queenofbabes]

What readings are these? Did you do an experiment yourself? Try describing it then!

 

[Scollitt]

I conducted the experiment as follows:
I dropped 0.005kg, 0.010kg and a 0.020kg balls from 0.25m and kept increasing the drop height by 0.25m after every reading.
I found that the lighter ball the made a deeper crater that those of a greater mass.
This somewhat puzzled me, so to investigate further I conducted the experiment with heavier balls (0.030kg, 0.050kg and 0.070kg) and the reading read the same.

Does anyone know why a deeper crater is formed using a lighter ball?

Steve

 

[queenofbabes]

Are all your balls of the same size? What are you dropping it into? Sand?

 

[negitron]

Are all your balls of the same size?

I suspect this is the key question.

A related question: Drive a nail into a 2 x 4. Now, cut the point off a similar nail and drive it into the same piece of wood. What's the difference?

 

[Mstreman]

If you are modeling impact craters for 10m and larger diameter meteoroids/asteroids: A factor which cannot be adjusted in your current model is that larger objects/meteoroids/asteroids retain more cosmic velocity/momentum than do smaller ones. Depending on scale you may have to resort to a gun/catapult/ air piston to correct and control this velocity difference. Also a larger diameter object affects the vectors for potential ejecta by trapping rebound. The ejecta is trapped by the larger object's surface area and your vector energies tend to compress the target material vs eject them from the crater depression. Consider using a layer of flour over the sand to see the difference the density and compressibility of the target material composition has on crater formation. A quartz-sand target medium, while easier and cheaper to work with, introduces scale fit issues as a bedrock simulant substantially different then the scale fit for velocities and diameters of your model missiles. Some have used stacked sheets of"play dough" in different colors as it preserves identity of the layer it was ejected from and preserves ground wave/distortions at higher velocities. Plus it can be cross-sectioned for analysis. Finally be it remembered that strike angle for astroblemes is rarely vertical, for whatever that is worth to your experiment design