Physics - Ch 4
Lawsem ofC M1 otion
Easy notes with m es ( lass 1 Physics, Chapter 4)
Chapter in one line: Force changes motion. N o force, no change!
1. A ristotle's Fallacy
• Aristotle thought: "Force is needed to keep things moving." (WRONG !)
• Truth: things stop because of friction, not because force ran out.
• No friction → no force needed to keep moving.
MEME: Aristotle: "Moving things need a push!" Galileo: "Bro, you forgot
friction exists."
2. Law of Inertia & Newton's 1st Law
Every body stays at rest or in uniform straight-line motion unless an external force acts
on it.
• Inertia = resistance to change (basically the laziness of objects).
• Net force = 0 → acceleration = 0.
• R est and uniform motion are the same thing for physics.
• Bus starts suddenly → you fall backward (body wants to stay at rest).
• Bus stops suddenly → you fall forward (body wants to keep moving).
MEM E: Teacher at 7 AM: "Wake up!" M e: "Newton's 1st Law, sir. I need an
external force."
3. M omentum (p)
p = m × v (mass × velocity). It is a vector. Unit: kg m/s.
• Heavy + fast = hard to stop.
• A cricketer pulls his hands back w hile catching to increase the time, so the force is
smaller.
-1-
Lawsem ofC M1 otion
Easy notes with m es ( lass 1 Physics, Chapter 4)
Chapter in one line: Force changes motion. N o force, no change!
1. A ristotle's Fallacy
• Aristotle thought: "Force is needed to keep things moving." (WRONG !)
• Truth: things stop because of friction, not because force ran out.
• No friction → no force needed to keep moving.
MEME: Aristotle: "Moving things need a push!" Galileo: "Bro, you forgot
friction exists."
2. Law of Inertia & Newton's 1st Law
Every body stays at rest or in uniform straight-line motion unless an external force acts
on it.
• Inertia = resistance to change (basically the laziness of objects).
• Net force = 0 → acceleration = 0.
• R est and uniform motion are the same thing for physics.
• Bus starts suddenly → you fall backward (body wants to stay at rest).
• Bus stops suddenly → you fall forward (body wants to keep moving).
MEM E: Teacher at 7 AM: "Wake up!" M e: "Newton's 1st Law, sir. I need an
external force."
3. M omentum (p)
p = m × v (mass × velocity). It is a vector. Unit: kg m/s.
• Heavy + fast = hard to stop.
• A cricketer pulls his hands back w hile catching to increase the time, so the force is
smaller.
-1-
