Estimate the moment of inertia of the door of the classroom.How does this change if a 5kg monkey is hanging on the doorknob? How does it change if the monkey is hanging on the hinge?
The moment of inertia is an objects tendency to resist changes in motion, while trying to rotate the object. This would apply to the example of the class room door, as it rotates around on its hinges. The more massive the door, the larger its moment of inertia, meaning it will take more force to get the door to open, and require more force to get the door to stop once it is rotating. If you add a 5 kilogram monkey to the doorknob it will increase the amount of force needed to rotate the door. If the monkey is positioned by the hinges, it will require a lesser force than it would with the positioning of the monkey on the door knob. Newtons first law of motion is known as the law of inertia, while the second law of motion is involved with the force needed to move a certain mass at a certain acceleration. Things with more mass will have more inertia, requiring a larger force to either get them moving, or to stop them once they are moving.