Law of inertia - Some other examples of moment of inertia

Law of inertia

Inertia is a measure of a body. The greater the mass of a body greater its inertia or vice versa when any vehicle starts suddenly, the passenger falls backward. It is due to the inertia property of the body.

     The persistence of all matter to remain at rest when left alone or to keep in motion after being acted on by an outside force is called inertia. Inertia is a definite characteristic of all matter whether solid, liquid, or gas. Newton’s first law may now be restated as follows:

Everybody persists in a state of rest or of uniform motion in a straight line, unless compelled by some outside force to change that state.

    Since mass is the resistance to motion in a body, it follows that the more mass a body has the more inertia it will have. You cannot start a freight car moving all by yourself because you cannot produce the force necessary to overcome its huge inertia.

      If some powerful force starts this car and lets it roll along the tracks by itself, you won’t be able to stop it immediately by yourself because its persistence to keep in motion is just as great as its persistence to remain at rest, and it will take as much outside force to stop it as it did to start it. The car will eventually stop because of the friction of the wheels on the track and the rubbing of the axles against the car.

Some other examples of moment of inertia

     If you want your automobile to stop suddenly you don’t merely shut off the gas and let the car roll along until it comes to rest. You apply the brakes, and the tight brake bands, rubbing against the wheels of the car, produce sufficient friction to overcome the momentum of the car and quickly bring it to a stop. 

The same is true of a railroad train. When the air brakes are applied to all the cars friction soon overcomes the inertia of the massive train and brings it to a stop. If you happen to be standing in one of the cars and the brakes are applied very suddenly, you will fall forward. This is because your body is going with the speed of the train and your feet are in contact with the floor of the car. 

When the car slows up suddenly, your feet do the same, but the rest of your body cannot keep up with your feet and consequently keeps on moving forward. One of the most dramatic uses of this effect is in the accelerator, an instrument that employs inertia to measure linear motion, and is vital in the inertial navigation systems that now guide aircraft, rockets, and ships.