video credits:
https://www.youtube.com/watch?v=2PNSj-GJ2vY
https://www.youtube.com/watch?v=ppEiWxhuFi8
https://www.youtube.com/watch?v=ai-bR2h-tgQ
https://www.youtube.com/watch?v=T5g8XIt7LJk
https://www.youtube.com/watch?v=g4e1PcTxNRU
https://www.youtube.com/watch?v=GZuTw4hE7TE
https://www.youtube.com/watch?v=NScWXVa4i5o