Evenifyouareagoodhigh-jumper,youcanjumponlyaboutseven...
问题详情：Evenifyouareagoodhigh-jumper,youcanjumponlyaboutsevenfeetofftheground.Youcannotjumpanyhigherbecausetheearthpullsyouhard.Thepulloftheearthiscalledgravity.Youcaneasilyfindoutthepulloftheearth.If...