TE Enriched Sample (E)

Apparent weightlessness • Acceleration due to gravity is independent of the mass of the object. & An orbiting spacecraft and all of the things inside have a common acceleration. & The spacecraft does not exert any reaction force on all of the things inside. & The things inside are apparently weightless. Keywords aphelion 遠日點 ellipse 橢圓形 escape speed 逃逸速率 focus ( pl . foci) 焦點 gravitational potential energy 引力勢能 Kepler ’ s laws of planetary motion 開普勒行星運動定律 law of universal gravitation 萬有引力定律 perihelion 近日點 semi-major axis ( pl . axes) 半長軸 Common Mistakes • Elliptical orbit uniform speed along whole orbit near the Sun: faster far from the Sun: slower speed = v speed = v planet Sun speed < v According to Kepler’s second law, the speed of a planet in an elliptical orbit is not constant . • When applying Kepler’s 3rd law Sun Mars Phobos Apply it directly Mars and Phobos rotate around di erent objects Ö di erent proportionality constants Ñ T Phobos T Mars ( ) 2 a Phobos a Mars = ( ) 3 When applying Kepler’s third law to orbital motion around different celestial bodies, the proportionality constants will be different. • Why feel weightless? too far from the Earth & F g . zero both free fall towards the Earth & no reaction on the man Earth Earth Inside a spacecraft orbiting around the Earth, the feeling of weightlessness arises because no reaction exerts on the person (and all of the things) inside. Orbital Motions under Gravity 3 90 Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.