- It is the inability of a body to change by itself, its state of rest. This means a body at rest remains at rest and cannot start moving by its own.
EXAMPLE- A person who is standing freely in bus, thrown backward, when bus starts suddenly.
When a bus suddenly starts, the force responsible for bringing bus in motion is also transmitted to lower part of body, so this part of the body comes in motion along with the bus. While the upper half of body (say above the waist) receives no force to overcome inertia of rest and so it stays in its original position. Thus there is a relative displacement between the two parts of the body and it appears as if the upper part of the body has been thrown backward.
NOTE- If the motion of the bus is slow, the inertia of motion will be transmitted to the body of the person uniformly and so the entire body of the person will come in motion with the bus and the person will not experience any jerk.