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Physics/Train Derailment Example.


Dear Prof Steve's_laws_of_motion‎‎

Example : Rocket launching is example of Sir Issac Newton's
Third Law of Motion.

Examples :

1. Train running at 300 km/hr speed may get derailed by applying Sudden Brakes manually by motorman or automated.

2. Automobile viz Car, Truck etc is moving at 150 km/hr speed. Human Beings sitting in the automobile experience a forward push when sudden brakes are applied by the driver.

i.e. Body having mass moving at maximum speed is suddenly brought
to rest by applying resist force (apply brakes).

The above two examples best illustrates which Sir Issac Newton's three Laws of motion, Law of conservation of momentum etc ?.

Awaiting your reply,

Thanks & Regards,
Prashant S Akerkar

Hello Prashant,

Unfortunately, the teachertech link did not work.

The derailment of example 1 is hypothetical. I don't know what anomaly might cause such a hypothetical accident. As I said before, there must have been a serious error in an engineering design (or poor maintenance) for this to happen. Without knowing what went wrong, I can't say what physical law might be involved in the explanation of the accident.

Example 2 is the result of Newton's 1st Law. The Human Beings tend to consider their reference system to be the car. But when their reference system decelerates, it becomes what is known as a non-inertial reference frame. Discussing the experience of Human Beings in such a reference frame often leads to introducing fictitious forces. See the site

I prefer to paraphrase a common way of stating Newton's 1st Law: that the humans in the car continue in motion in a straight line, at the same speed, until acted on by an outside force. The car decelerates, but they do not -- immediately. The outside force in this case would be provided by the seat belt becoming tight and that causes them to also decelerate.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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