This is not a homework question. I attempted to draw a free body diagram for a person pulling or pushing a cart.
Based on Newton's third law, the following forces act on the body of the person:
- forward reaction force done by the ground because of friction between the person and the ground.
- downward force (the person's weight) done by the earth.
- backward reaction force done by the cart.
I am wondering why the body of the person must be tilted forward. I have not seen any relationship between this posture with the magnitude of the forces acting on the person.
Could you tell me why the person's body must be tilted forward? How does this posture provide mechanical advantages?
Best Answer
It adds a horizontal component to the vertical force exerted by your legs.
When you're standing straight up, the forces exerted by your legs are straight up and down. Your legs are designed to exert a force to counter your bodyweight and allow you to stand like this, so they're quite strong at countering this force.
When you're leaning over like this, each step you take restores you a leaning version of standing straight position, and it allows you to exert this standing-up force your legs exert in a horizontal direction - in each of these pictures, you can see the person with one leg straight back, and the other bent in front of it; at the completion of each step, you could consider them to be standing with both legs straight back for a brief moment before they move the next leg.