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.
When the Occupational Safety and Health Act passed in 1970, steel-toe boots became a standard in the American workplace, preventing thousands of on-the-job injuries. Today's technology has only increased the variety of work boots available, and it's important to understand the differences before purchasing a pair.
If shoes are tattered and worn, the toes are poking through the sides, the steel toe is visible through the leather, then common sense tells you it's time to get a new pair of shoes, Lubart says. The same could be said for evaluating the tread on a slip-resistant safety shoe.