The cost of polypropylene per pound can fluctuate significantly due to factors such as crude oil prices, demand in various industries (like automotive and packaging), and global economic conditions. As of my last knowledge update in 2023, prices generally ranged from $0.50 to $0.80 per pound for bulk quantities in the United States. It's important to note that prices can vary based on the grade of polypropylene and the volume of the purchase. For smaller quantities or specialized grades, prices can be higher. For the most accurate and current pricing, contacting suppliers directly or checking market reports is recommended, as these figures can quickly become outdated due to market volatility.

The title of the fastest engine in the world currently belongs to the scramjet engine, specifically exemplified by NASA's X-43A. This experimental aircraft reached a record-breaking speed of Mach 9.6 (approximately 7,000 miles per hour) in 2004. Scramjet stands for Supersonic Combustion Ramjet—a technology enabling sustained hypersonic flight by mixing fuel with high-speed air while traveling faster than the speed of sound. Unlike traditional rocket engines that carry both fuel and an oxidizer, scramjets draw oxygen from the atmosphere, significantly reducing weight and potentially revolutionizing high-speed travel and access to space. While the practical applications of scramjets are still under development, their capability to achieve unparalleled speeds positions them at the forefront of aerospace technology.

Oatey PVC glue, known for its strong bonding properties, often stipulates a set drying time to achieve optimal adhesion. The initial set time can range from 15 minutes for smaller diameter pipes (up to 3 inches) to 2 hours for larger fittings. However, for full cure and maximum strength, a 24-hour period is generally recommended, especially under pressure situations or varying temperature conditions. Factors such as humidity, temperature, and the size of the PVC being bonded will influence the drying time. In colder environments, the curing process may be slowed, requiring additional time before the joint is subjected to pressure. Always refer to the specific product instructions for the best results, and ensure proper ventilation during application.