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Engineering ToolBox – Resources, Tools and Basic Information for Engineering and Design of Technical Applications!
Density is defined as mass per unit volume. Mass is a property and the SI unit for density is [kg/m3].
Density can be expressed as
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It’s hard to believe that things haven’t always been the way they are today. That they are thus because someone made them thus. Let’s take paper shredders as an example. Every time you use one , you do so somewhat unconsciously. Have you ever wondered where this fantastic machine came from?
No doubt it feels ageless. But that’s a misleading instinct. The paper shredder is a fairly new invention. Barely a century old, in fact. Who was the man that conceived it? Our questions take us, first to ancient Egypt where the art of writing on paper was first invented. After that, we will look at the activities of two individuals during the first half of the twentieth century.
The ancient Egyptians did not invent paper shredder. They developed a form of paper known as papyrus. No doubt, even in that era, people made mistakes when writing. I am also confident that sensitive knowledge, such as messages meant only for the pharaoh and his most trusted ministers, was also recorded in those days.