The umbrella is curved such that the air is being reflected backwards. If the umbrella stopped the air or pushed sideways but not backwards, then that initial F would be cancelled out. But because it's being reflected backwards you get an extra F, and that's what propels you forward.
LOL. You can't create energy from nothing. If the force from an energy source is X, you can't get 2X without external energy.
The force of the air expelled from the leafblower is pushing backwards (Newton's third law and all). Even if the umbrella captured every molecule of air that was affected by the leaf blower and redirected every joule of energy directly back (and it does neither), the forces perfectly cancel.
I've explained this several times already and you're too retarded to understand.
What you're describing isn't possible. There's a reason ships don't have giant fans blowing on sails.
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