For evolution to occur:
There must be genetic variation in a population. This provides variation on which natural selection can act. Then natural selection can act by selecting those species which are better adapted to the environmental conditions. Over time those animals that are best suited to the environment only will survive and reproduce. Those organisms successful genes will be preserved and eventually the gene frequency in the population will change, changing the overall characteristics of a population. This is how evolution occurs.
When the ride is at the top of its pole, it has all potential energy. When it is in the middle, at 34 meters, it has 50% potential energy and 50% kinetic energy. When the ride is almost at the bottom, it has kinetic energy that turns into potential energy as it reaches the end.
Iguanas have spines along their backs to help protect them from predators. They also have a bunch of extra skin below their necks called a dewlap. This dewlap helps them to regulate their temperature, which is helpful as they are cold-blooded and their bodies don't control their body temperature automatically.
Your body can use it in a better way then just having it just sit there