04-Relative_Space_Time

04-Relative_Space_Time - Relativity Relativity Biology190A...

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elativity Relativity Biology 190A Lecture 4 ‐‐‐ Prof. Steve Schneider Dept. of Astronomy
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Our Understanding of Nature before 1900 atter+Energy There are objects that can move and interact with each other. Matter+Energy Albert Einstein There are forces that cause or allow these objects to interact. It seemed that all the basic forces and particles had been discovered, and just details remained. ut our nderstanding was But our understanding was about to be overthrown… Space+Time=Spacetime Albert Einstein
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What is “Relativity”? Relativity is an idea that goes back at least to Galileo in the 1600s, and probably even earlier. It describes the ways that events will appear to ifferent observers. different observers. Relativity in physics does NOT say or imply: t h i i lt i Everything is relative. We all perceive time differently. It is impossible for objects to move apart at greater than the speed of light. So what is relativity?
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Frames of Reference easurements of Measurements of direction and speed are made relative to thi l something else, usually our own frame of reference . A ball rolling down the aisle of an airplane has different “speeds” relative to the plane or ground And r that speeds relative to the plane or ground. And for that matter the Earth’s surface is spinning at about 1650 km/hr and the Earth is moving around the Sun at about 108,000 4 km/hr and the Sun is circling the center of our galaxy at about 800,000 km/hr, . ..
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alilean Relativity Galilean Relativity Positions and motions seen by one observer can be converted to another observer’s point of view by “vector addition” of the relative positions and motions. No observer’s reference frame is more special than any other observer’s frame. (And it has usually been assumed that time is 5 measured the same way by all observers.)
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in standard relativity we can dd or subtract add or subtract speeds Velocities in Different Frames speed of ball is 10 km/hr in frame of spaceship
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ewton’s Laws Revisited Newton s Laws Revisited Nothing about the idea of relativity is inconsistent with Newton’s laws of motion. 1 st Law says an object at rest stays at rest, or in otion stays in motion at the same speed and motion stays in motion at the same speed and direction. It’s just that observers in different ames have different definitions of “at rest ” frames have different definitions of at rest.
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04-Relative_Space_Time - Relativity Relativity Biology190A...

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