Shellfish that was abundant in the cambrian like a horse crab

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on

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Photosynthesisthe process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.