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CM [009] Newton's First Law
The document discusses Newton's First Law of Motion, which states that a particle at rest will remain at rest unless acted upon by an external force, and a particle in uniform rectilinear motion will continue moving at a constant speed unless compelled to change by forces. It emphasizes that motion is fundamentally based on momentum rather than force and suggests a modified version of the law that integrates parts of the original description. Additionally, it outlines corollaries regarding momentum conservation and its influence on objects in motion.
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CM [009] Newton's First Law
- 1. © ABCC Australia2015 new-physics.com NEWTON’S 1ST LAWS OF MOTION CM [009]
- 2. © ABCC Australia2015 new-physics.com [and] a particle in uniform rectilinear motion will continue to move on forever at constant speed in the same manner. Newton’s First Law in 3 Parts A particle in rest will remain forever at rest It will change its state of motion only and only when it is compelled to do so by forces impressed on it. Law No. 1 can be more conveniently studied in three parts I , II, & III.
- 3. © ABCC Australia2015 new-physics.com Newton’s First Law : Part 1 A particle will remain at rest and stays like that forever. Why is it not moving? Because it is in the situation when there no momentum. So a particle at rest is not a special case of motion. It is a motion with 0 momentum. A particle in rest will remain forever at rest 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 = 0 So momentum: 𝑝𝑝 = 𝑚𝑚𝑚𝑚 = 0 So I am not moving
- 4. © ABCC Australia2015 new-physics.com [and] a particle in uniform rectilinear motion will continue to move on forever at constant speed in the same manner. Newton’s First Law : Part 2 This is the old description of impetus and conservation familiar to John Philoponus, Jean Buridan, Descartes and Galileo Galilee. This will be studied in the coming sections.
- 5. © ABCC Australia2015 new-physics.com Newton’s First Law : Part 3 It will change its state of motion only and only when it is compelled to do so by forces impressed on it. This part deals with force and its effect on the object’s state of motion. So it is also to be dealt with in a later section on force and acceleration.
- 6. © ABCC Australia2015 new-physics.com Law 1 Part 3 Law 2 Law 3 Sequence of Analysing Newton’s Law We start from here!
- 7. © ABCC Australia2015 new-physics.com Newton’s First Law : Part 1 A particle in rest will remain forever at rest This is not an independent case. It is only a special case when momentum is equal to zero. So it can be incorporated into Part 2 as a subsidiary, saying: When a particle has no momentum, it will not move, thus remains at rest. 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 = 0 So momentum: 𝑚𝑚𝑚𝑚 = 0 So the object is not moving
- 8. © ABCC Australia2015 new-physics.com [and] a particle in uniform rectilinear motion will continue to move on forever at constant speed in the same manner. Newton’s First Law : Part 2 This phenomenon had been demonstrated by Galileo before in his ramp experiment. When there is no friction and air resistance, the ball will move on forever.
- 9. © ABCC Australia2015 new-physics.com Comparison When we compare this modified law with Newton’s original one, it can be seen that the latter is a description of a physical phenomenon. The new law spells out the more basic elements that is affecting motion. First we have the motion, then we have the event described by Newton’s First Law. Momentum A particle in rest will remain forever at rest, and a particle in uniform rectilinear motion will continue to move on forever at constant speed in the same manner. It will change its state of motion only and only when it is compelled to do so by forces impressed on it. An object is moved by its momentum. Newton’s Modified First Law Newton’s Old Descriptive First Law
- 10. © ABCC Australia2015 new-physics.com Newton’s First Law of Motion - Modified By eliminating Part 3 and incorporating Part 1 into Part 2, we have a more basic law of motion – Law No. 1: An object is moved by its momentum. The other situations can be written as corollaries: i. Momentum never fades away and so is conserved. ii. When momentum is zero, the object will be rest. iii. An object travels at the direction of its momentum. iv. Since momentum is conserved, constant motion is for ever.
- 11. © ABCC Australia2015 new-physics.com Object Carried by Momentum Instead of saying an object is motivated by its momentum, it is more correctly to say that an object is carried by its momentum: like a man carried by a swan or a saint carried by angels.
- 12. © ABCC Australia2015 new-physics.com . . . and the deeper foundation of the First Law of motion is momentum, not force.
- 13. © ABCC Australia2015 new-physics.com NEWTON’S 2ND LAW OF MOTION To be continued on: [010] ABCC