An image of
th evolutionary history of the horse

The Rise of Horses

The horse of today is a far-cry from its ancestors. The beginning of the equine evolutionary line, Eohippus, was a multi-toed bounding creature that stood only a couple feet high. Eohippus lived in damp tropical forests. However, as North America, the hub of equine evolution, moved north, these forests were replaced by open grasslands. This lead to the evolution of the current horse. Multiple toes were no longer needed to distribute weight over soggy ground; one toe was better for resisting the impact of more solid ground. Other developments included adapting several gaits for covering ground as well as larger size.
Without artificial selection, modern horses would look most like the Przewalski's horse, often called the last true wild horse. Horses have played a big role in the improvement of early human society, from boosting crop/livestock output from their use in agriculture, to increasing long distance travel in the use of carriages, to giving the upper hand in early wars though cavalry.

The Physics of Equine Locomotion

The development of several gaits, the walk, amble, trot, canter, and gallop, was necessary for efficiently moving in response to different situations. The motion of each of these gaits is unique and apply different physics involving force, elasticity and other concepts. There were also several anatomical changes that were very important in changing from mostly bounding and short sprints, like in Eohippus, to the the long distance travel of modern horses. Many of these adaptions have to do with resisting the increased forces of hard ground and covering ground in an energy efficient manner, concepts that heavily involve physics.

Image source:https://kids.britannica.com/kids/assembly/view/241551