Short answers, pulled from the story.
Capital goods are durable produced assets used to create other goods or services. These items provide productive services over many years unlike raw materials that vanish in a single production cycle.
Adam Smith wrote about fixed capital and circulating capital in his 1776 work Wealth of Nations Book II Chapter 1. He distinguished between assets not consumed during production like machines and those that were like raw materials.
Karl Marx classified constant capital as referring specifically to capital goods such as plant and machinery. Variable capital referred to labor inputs where costs varied based on wages paid during employment.
Modern economic theory includes human capital from skills and education intellectual property natural capital from geology and living organisms social capital from inter-relationships financial capital from obligations traded in markets and public capital from government-owned assets.
Economists at MIT and the University of Cambridge debated how to measure heterogeneous capital goods because no basis exists for aggregating these varied objects into a single metric. Critics argued that combining different types of assets creates theoretical inconsistencies within production functions.