It is typical to find in numerous movies that a forceful hug might break another person’s ribs. How strong must we be to embrace someone till their ribs begin to crack?
Although the ribs are armor that shields the body’s critical organs, they are more prone to fractures than the strong thigh bones. Chest compressions used during CPR have a potential of fracturing the sternum or ribs, in addition to some intense competitive sports that can result in rib accidents. This suggests that breaking ribs with just human strength is achievable.
Knowing precisely when something may break is an issue that many engineers face on a regular basis. However, every time one of these tests is completed, a portion of the material is destroyed, and most of the time there is no way to conduct the experiment (such as large building structures, or the ribs of innocent humans).
So, we may investigate whether ribs in humans can unintentionally shatter during a hug using some straightforward estimations.
Fracture mechanics
Typically, when a solid material is subjected to an external force, it will first experience an elastic deformation corresponding to the strength of the force before being able to return to its initial state. According to the formula “external force = stiffness * displacement ^ 2.” The lesser the deformation under a given external force, the harder the material.
The microstructure inside the material is often destroyed when the external force is sufficiently strong to create irreversible plastic deformation. A material’s strength is the highest stress that it can endure without breaking.
Glass, for example, is brittle but hard, with a high hardness but low strength. It is difficult to deform but will break under severe stress; On the other hand, metal tends to have greater strength and a wider elastic range.
Hardness and strength are related but distinct concepts, and strength is the main focus of the discussion on fracture.
Human bones
Bones are a complex organic structure, hence their mechanical characteristics are more complex than those described above. When the bone is struck by outside forces, the energy can be distributed through local plastic deformation, making it harder for the crack to spread. In other words, the speed of the force as well as the force’s size both affect whether a fracture occurs. A sudden smash won’t allow the energy to dissipate in time, making it easier for the material to break.
Age, sex, and other individual differences affect the flexural strength of human bones, although the average value is between 40 and 80 mPa.
The power of a hug
The power that a typical person can apply with one hand viries. Chest Fly uses almost the same muscle group as hugging. The average dumbbell fly weight for a male lifter is 52 lb (1 RM). This makes you intermediate on a strength level and is a very impressive lift, which indicates that one rib must support about ten kilos of force if the power is applied to two ribs.
According to common sense, thinner materials are more likely to break, and the amount of force a given material can sustain before breaking should be inversely correlated to its cross-sectional area. In other words, the force per unit of cross-sectional area, or the concept of stress, is what actually determines the strength of the break (pressure). If a rib’s portion were just a one-centimeter square, the pressure would be equal to:
100 Newton/cm2 = 106 Newton/meter2 = 1 mPa
But in addition to taking into account the cross-sectional area, the ribs act more like a bridge with both ends fixed and hanging in the middle. We can infer from daily experience that the bend will be more severe if the longer the length between each end(L) and the thinner the thickness(d).
In order to calculate the bending stress that the ribs in the structure are subjected to, the tension is multiplied by a ratio of length to thickness. We can get the final numbers, 10 mPa, by timing 1 mPa with 10, based on the assumption that the ribs are roughly 10 centimeters long.
In comparison to the rib strength mentioned above, we need at least four times the power of a chest fly that a strong man can produce to crash one’s ribs, which is nearly impossible.