friction and rolling resistance, and work done queries

sgstudent

Hi tiny tim! I thought the static friction of the push is the friction from the ground?

tiny-tim

well, you push the wheel of a wheelchair using static friction also (and there's static friction on the seat)

anyway, nothing equals anything else unless the acceleration is zero

sgstudent

Oh but since the friction acting on the wheels by the ground is also static friction, then shouldn't there be a push force that is equal to the friction on the ground? What would that push force be and since the push force is equal to the static friction on the wheel how can there be a net force?

tiny-tim

hi sgstudent! happy new year!
no, the push force P on the top of the wheel is forward

and the friction F from the ground is also forward

for example, if there is a horizontal wind resistance force of W, and if the acceleration is zero,

then P = F (because the angular acceleration is zero), and so P = W/2