posted by Keyshia .
What two sources of friction do you have to overcome when you are walking?
I did not see your question earlier.
Air friction and internal friction in the joints of the body, especially the knees and ankles, must be overcome when walking. Neither are very large at normal walking speeds.
The friction of your feet on the ground does not have to be overcome unless there is slipping; that it is what pushes the body forward.