Author: Edgar Zhu
Editors: Vincent Chang and Megan Liu
Artist: Daisy Zheng
Picture this: two identical glass bottles—one filled with water and the other empty—are falling from the same height. Which bottle is more likely to break? Given that the amount of water in the bottle is relatively small compared to that of the bottle, the common answer is that the bottle full of water is less likely to break. There are two major factors behind this phenomenon.
Two forms of deformation are elastic deformation and plastic deformation. Elastic deformation is when an object can return to its original state after being removed from an external force. Every object has an elastic limit, or the maximum extent that a force can act on an object without the permanent alteration of its shape. If an object exceeds this elastic limit, it will not be able to restore its original shape.
Plastic deformation is when an object exceeds the elastic limit. For example, plastic deformation occurs when a bottle breaks.
Another important concept to understand is the compression of a substance. Different substances require different levels of force to be compressed because of their difference in intermolecular forces. For example, water is a substance that is hard to compress. To put this into perspective, at a depth of 4,000 meters, the volume of water decreases by only 1.8 percent at 40 MPa. So, the force from the collision between the bottle and ground to make any changes to the volume of the water in the bottle is relatively insignificant.
During the collision, water cannot be compressed so it provides a force that cancels part of the collision force. A smaller collision force would not attain the limit of plastic deformation. Therefore, the bottle with plenty of water in it will be less likely to break.
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