Question

Why does a child in a wagon seems to fall backward when you give the wagon a sharp pull forward?

Short answer

According to Newton’s law, the child’s upper body will stay at rest, but its feet will start moving as they are in contact with the wagon.

Step-by-step solution

Step 1. Newton’s first law

Newton’s first law mentions that any object does not change its state of motion or rest until acted upon by an external force.

Step 2. Explanation of boy falling forward

As the wagon moves forward, an acceleration in the forward direction is applied, but no force is applied to the boy. Thus, according to Newton’s first law, it will stay at rest.

However, as the feet of the boy are in contact with the wagon, due to friction, they will start moving forward. Since his upper body moving is still at rest, the child will start falling back.