Physics
Physics
Problem
When a person walks forward on level ground without slipping, the friction acting on the sole of the shoe is a) static and directed backward b) zero, since there is no slipping c) static and directed forward d) kinetic and directed forwardIntuitive explanation
The key insight here is recognizing that friction isn't always the "bad guy" that opposes motion—it's actually what enables forward walking. When your foot pushes backward against the ground, static friction acts forward on your shoe, accelerating your body ahead. Without this grip, you'd slip in place like on ice. The direction of friction is determined by what the ground must do to prevent your foot from sliding, not by the direction you're moving.
Intuitive explanation
The key insight here is recognizing that friction isn't always the "bad guy" that opposes motion—it's actually what enables forward walking. When your foot pushes backward against the ground, static friction acts forward on your shoe, accelerating your body ahead. Without this grip, you'd slip in place like on ice. The direction of friction is determined by what the ground must do to prevent your foot from sliding, not by the direction you're moving.