Changes

When an elastic material is strained, work is done on it and energy is stored in it.  Elastic energy is a form of potential energy.  A rubber ball falling on to a hard surface converts what was previously kinetic energy into elastic energy on impact.  This elastic energy is released again as kinetic energy when the ball bounces.  The ball does not, however, attain the same height as previously.  The elastic framework of an animal’s body behaves similarly, as it bounces up and down during running (Fig. 2.4).  Some of the kinetic energy is lost as heat.  The less energy lost in this way, the greater the elastic resilience of the material.  Resilience is the work recovered from a material in elastic recoil, expressed as a percentage of the work previously done in straining it (Fig. 2.5).  Passive musculoskeletal tissues should be as resilient as possible, to conserve energy.  

When an elastic material is strained, work is done on it and energy is stored in it.  Elastic energy is a form of potential energy.  A rubber ball falling on to a hard surface converts what was previously kinetic energy into elastic energy on impact.  This elastic energy is released again as kinetic energy when the ball bounces.  The ball does not, however, attain the same height as previously.  The elastic framework of an animal’s body behaves similarly, as it bounces up and down during running (Fig. 2.4).  Some of the kinetic energy is lost as heat.  The less energy lost in this way, the greater the elastic resilience of the material.  Resilience is the work recovered from a material in elastic recoil, expressed as a percentage of the work previously done in straining it (Fig. 2.5).  Passive musculoskeletal tissues should be as resilient as possible, to conserve energy.  

:::::'''Fig. 2.3 Elasticity'''  

:::::'''Fig. 2.3 Elasticity'''  

:::::The force F tenses a block of material of transverse sectional area A and length l, producing a deformation e.  In Figure 2.3A, stress is proportional to strain.  The slope of this line is the elastic modulus.   

:::::The force F tenses a block of material of transverse sectional area A and length l, producing a deformation e.  In Figure 2.3A, stress is proportional to strain.  The slope of this line is the elastic modulus.   

:::::Upon removal of the stress, the block returns to its original shape.  The block is perfectly elastic.  In Figure 2.3B, the elastic modulus is not constant; with more stress, a disproportionate deformation is produced.   

:::::Upon removal of the stress, the block returns to its original shape.  The block is perfectly elastic.  In Figure 2.3B, the elastic modulus is not constant; with more stress, a disproportionate deformation is produced.   

:::::For this reason, and also because when the stress is removed some of the deformation remains, the block in this instance is imperfectly elastic.  Such a residual deformation is not useful in animal mechanics.  

:::::For this reason, and also because when the stress is removed some of the deformation remains, the block in this instance is imperfectly elastic.  Such a residual deformation is not useful in animal mechanics.

 

==='''Elastic resilience'''===

==='''Elastic resilience'''===