impulsion, impulse, drift, impulsive, impellent, incitative, bent, goad, excitant, invigorant, more...

hindrance, obstacle, deterrent, impediment, block

push, kick, nudge, shove, slap, slap in the face, kick in the pants, kick in the butt, more...

new, great, further, initial, fresh, major, strong, powerful, main, original, additional

forward momentum,   urgent prompting,   urge to action,   urging to action,   starting push,   a driving force,   force behind,   starting force,   initiating force,   primary force