The speed of sound depends on the medium that the waves pass through, and is a fundamental property of the material. The first significant effort towards the measure of the speed of sound was made by Newton.
These meet ASTM safety standards and are suitable for most professions. Composite. Many safety boots are nonmetallic-instead of steel or aluminum, they are reinforced with a composite-material steel toe boots, usually made with thermoplastic polyurethane (TPU) or similar materials.
The reinforcement is normally made of steel hence they are sometimes known as steel toe cap boots. These boots were invented at the end of World War II in Germany. These were originally meant for workers to help protect themselves as they worked. Before these boots were invented, workers used to wear leather boots or wooden clogs. Currently however several other users including civilians and the military personnel use these boots. The history of the safety boots can be traced back to the beginning of the 20th century at a time when people started addressing industrial safety issues. During this time the laws on compensation were enacted. Before this period, replacing an injured worker was cheaper and faster than introducing safety measures.