Why does a child in a wagon seems to fall backward when you give the wagon a sharp pull forward?
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.
Newton’s first law mentions that any object does not change its state of motion or rest until acted upon by an external force.
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.
A stone hangs by a fine thread from the ceiling, and a section of the same thread dangles from the bottom of the stone (Fig. 4–36). If a person gives a sharp pull on the dangling thread, where is the thread likely to break: below the stone or above it? What if the person gives a slow and steady pull? Explain your answers.
FIGURE 4-36 Question 9
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