What is the proof of the law of inertia?

[robby]

*Originally posted by FranticMad *
**The fact that we can send satellites into high orbit, and they stay there for a very long time, is a pretty convincing demonstration of inertia. **

This is actually not a very good example for Newton’s First Law (a.k.a the Law of Inertia). Newton’s First Law may be stated as: “An object at rest tends to stay at rest and an object in motion tends to stay in motion with constant velocity unless acted upon by a net external force.”

An orbiting satellite (in a circular orbit) has a constant net external force acting on it (the gravitational force of attraction on the satellite by the Earth), and the satellite is under a constant acceleration toward the center of the Earth. While the satellite’s speed may be constant, the velocity is not. (The direction of travel is constantly changing).

[Ring]

*Originally posted by robby *
**One example is the “Law of Conservation of Mass.” This law was experimentally invalidated with the advent of nuclear physics. **

It is unfortunate in the extreme, but nonetheless I feel I must say this; universally, mass is a conserved quantity.

[asterion]

*Originally posted by GTPhD1996 *
**Pravnik

The definition of acceleration is the rate of change of velocity. So if something is accelerating, it’s velocity is changing.

GTPhD1996 **

True, but velocity is a vector. Acceleration is a derivative of velocity. You can change a vector by changing its direction and leaving its speed intact.

Just pointing out that no one has brought up angular acceleration and velocity yet.