Question

Why is it easier to open adoor by applying a force at the end of it?

Answer 1

As distance increases, torque increases and so the rotational effect increases. Hence, it iseasier to push open a door by holding the knob than by pushing closer to the hinge. To explain it to a child, just explain that it's easier for aforce to work when it has some more "space" to move about than, when it doesn't

Answer 2

It is easier to open a door by applying the force at the free end of it because of the larger the perpendicular distance, less is the force needed to turn the body.