Keep a steady pace. If gravity weren't there, You'd float away in space. Gravity, Gravity, Keeps us on the ground. Light travels in straight lines, that is unless somehow it's turned. But that's quite eas'ly learned.
Refraction is the bending which is caused by changing speed.
When slowing down the light bends 'toward the normal' as they say. Energy like a stash in the bank. Frequency times the constant of Planck. Deck the lab and be of good cheer. With our Mechanics, Waves, and Heat, You've helped us a lot this year.