How Many Ways Can You Think of
to State Newton's First Law (the Law of Inertia)?
1. "Every object continues in its state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted on it." (Hewitt, Paul G., Conceptual Physics, Second Edition, p. 28)
2. "Things tend to keep on doing what they're already doing." (Hewitt, p. 29)
3. An object at rest tends to stay at rest, an object in motion tends to stay in motion.
4. Objects resist accelerations.
5. Objects don't like to accelerate.
6. Left to themselves, objects don't speed up, don't slow down, and don't change direction.
7. It requires an unbalanced force to change the velocity of an object.
8. An object at rest will stay at rest unless an unbalanced force acts on it. An object in motion will move at constant velocity unless an unbalanced force acts on it.
9. If an object has a constant velocity, then no unbalanced forces are pushing on it.
10. A force on an object tends to change it velocity. If no force pushes or pulls on an object (or if the forces on the object cancel each other out) then the object's velocity stays the same.
11. No unbalanced force means no acceleration.
12. No force means no acceleration.
13. If no forces act on an object (or if all of the forces that do act cancel each other out), then the object will not:
* speed up
* slow down
* change directions
14. Whatever an object is doing, that's what it wants to do. (Professor Julius Sumner Miller)
15. Objects don't accelerate unless "forced" to.
16. Objects don't change their velocity by themselves.
17. If an object is not accelerating, then either:
* no forces are pushing on it, or
* all of the forces that are pushing on it balance each other exactly.
18. If you see an object at rest, or moving in a straight line at constant speed, then you can conclude that either no forces are pushing on the object, or (more likely) all of the forces that are pushing or pulling on the object cancel each other out.
19. Consider a body on which no force acts. If the body is at rest, it will remain at rest. If the body is moving with constant velocity, it will continue to do so. (Halliday, Resnick, & Walker, Fundamentals of Physics, 5th Edition; p. 82)
20. If no force acts on a body, we can always find a reference frame in which that body has no acceleration. (Halliday, Resnick, & Walker, Fundamentals of Physics, 5th Edition; p. 82)
21. If nothing pushes on you, you won't accelerate (or decelerate, either).
22. If you leave an object at rest, it will "stay put" forever unless something pushes or pulls on it. If you start an object moving, it will keep moving at the same speed in the same direction forever unless something pushes or pulls on it.
23. The velocity of a free body is constant in time. (David Layzer, Constructing the Universe, Scientific American Library)
24. Object continue to do what they are doing unless acted upon by an outside force. (Jeremy Raver)
25. If Fnet = 0, then a = 0.
26. If there is no net force on an object it is in equilibrium, and vice versa.
27. Objects made of matter have inertia.
28. Inertia is a property of matter.
29. Objects like to be in equilibrium.
30. Things keep doin' what they're doin' 'til you mess with 'em. - David Charles Schaller