Answer this question: when you can not see what is taking place, but other senses indicate occurrences. this is called

the only real purpose of sputnik 1 was to beat the us into space. we were getting close to launching a useful satellite, explorer 1 - which launched on january 31, 1958. the ussr had to beat that, so they launched sputnik 1 on october 4, 19

conservation of mass

mass before something happens = mass afterwards

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray