Kelley used to do three sets of squats one time per week. after three weeks she noticed she was less sore than when she started this exercise. which principle is at work?

The principle underlying this change is called progression. This principle tells us that when your fitness level improves, your body has adjusted to your regular routine; thus, you will feel less sore than when you started the squats three weeks ago. During this time, your muscles have developed and your body has adopted to the stress brought about by your exercise. 

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .