Laws of Motion - Mechanics

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🚀 What is Dynamics?

Mechanics= The branch of physics that studies the motion of objects and their causes

📊 Divisions of Mechanics

Sect	English	Explanation	example
Mechanics	Kinematics	describing motion (without cause)	Velocity, acceleration, distance
Dialectics	Dynamics	Investigate the causes of movement	Force, Newton's laws
Status	Statics	Materials at rest	Balance, stability

📏 Basic operating parameters

Size	code	formula	SI unit	Type
Displacement	s	-	m	Vector
Distance	d	-	m	scalar
Speed	v	d/t	m/s	scalar
Velocity	v	s/t	m/s	Vector
Acceleration	a	Δv/t	m/s²	Vector

🎯 Scalar vs vector quantities

Scalar Quantities	Vector Quantities (Vector)
Distance Speed Mass Time Work Energy Power Temperature	Displacement Velocity Acceleration Force Momentum Weight Torque
🎯 Numeric value only	🎯 Numeric Value + Direction

🎯 TNPSC Shortcut - "SMART WEP"

Scalar - "SMART WEP":
S- Speed
M- Mass
A- Area
R- (Reserved)
T- Time, Temperature
W- Work
E- Energy
P- Power

📝 Important questions

Q:What type of measure is velocity?
A:Vector size (Vector) ✅

Q:What type of job size?
A:Scalar size (Scalar) ✅

Q:What type of size is the key?
A:Vector size (Vector) ✅

🍎 Newton's Laws of Motion

Sir Isaac Newton (1642-1727)- England
Thread:Principia Mathematica (1687)
Famous story:The apple fell! 🍎

📜 First Law - Law of Inertia

"An object is at rest if it is at rest, and if it is in motion it will continue to move in a straight line with constant velocity - unless an external force acts on it"

Key point	Explanation	example
Inertia	Reluctance to change position	Leaning forward when the bus stops suddenly
Rest materialism	Wanting to rest	Keeping the book still on the table
Movement material	Wanting to be in motion	A running ball keeps rolling

🎯 Reminder – “Materialism = Laziness”

Object is lazy - doesn't want to change its state! 😴

📜 Second Law - Law of Force

"The rate of change of momentum of an object is directly proportional to the force acting on it and is in the direction of the force"

F = ma

Force = Mass × Acceleration
Force = Mass × Acceleration

Size	If increased	example
Force (F) ↑	Acceleration (a) ↑	Push harder and go faster
Mass (m) ↑	Acceleration (a) ↓	Difficulty pushing a heavy object

🎯 Remembrance formula

"FMA" = Force = Mass × Acceleration
"Force = Mass × Acceleration"

📜 Third Law - Law of Action-Reaction

"For every reaction there is an equal and opposite reaction"

Action	Reaction
The gun ejects the bullet	The gun will be pushed back 🔫
The rocket pushes the gas down	The rocket will go up 🚀
A swimmer pushes water back	Water pushes him forward 🏊
When we walk we push off the ground	The ground will push us forward 🚶
The bird beats the wind down	The wind will lift the bird up 🐦

🎯 Remember

"Every Action Has Equal and Opposite Reaction"
"If you get hit, you get hit back!" 👊↔️👊

📊 Rule of Three - Comparison

fate	Name	Key point	Formula/Comment
1st	Physical law	Object resists change of state	Inertia
2nd	Law of force	Force = rate of change of momentum	F = ma
3rd	Law of reaction	Verb = reaction	Action = Reaction

📐 Equations of Motion

Codes:
u = initial velocity
v = Final velocity
a = Acceleration
t = Time
s = Displacement

📊 Three equations of motion

No	Eq	application	Memory Trick
1	v = u + at	find v (without s)	🎯 "Wuw Aud" (VUA T)
2	s = ut + ½at²	Find s (without v)	🎯 "Suit Half Odd Square"
3	v² = u² + 2as	Find v (without t)	🎯 "V Squared = U Squared + 2as"

🎯 Equation Test - Quick Guide

Don't know what?	Which equation?
s don't know	v = u + at
v don't know	s = ut + ½at²
t don't know	v² = u² + 2as

🆓 Free Fall

Gravitational Acceleration (g)=9.8 m/s²≈ 10 m/s²

In free fall: a = g, u = 0

Eq	Free fall (u=0)
v = u + at	v = gt
s = ut + ½at²	h = ½gt²
v² = u² + 2as	v² = 2gh

💫 Momentum

p = mv

Momentum = Mass × Velocity
Momentum = Mass × Velocity
Unit:kg·m/s

📊 Law of Conservation of Momentum

"In a system with no external force, total momentum before collision = total momentum after collision"

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

Types of Collision

Type	momentum	kinetic energy	example
Re-conflict (Elastic)	✅ Does not perish	✅ Does not perish	Billiard balls 🎱
Re-conflict (Inelastic)	✅ Does not perish	❌ Decrease	Clay Ball Clash
A full rebound collision (Perfectly Inelastic)	✅ Does not perish	❌ will decrease more	Merging two things together

🎯 Memory Trick

"Momentum never dies!"
No matter the type of conflict, momentum is never destroyed.
Only kinetic energy is not destroyed in collisions.

💪 Types of Forces

📊 Classification of keys

Type of key	Explanation	example	formula
Earth's gravity (Gravitational Force)	Attraction between two masses	Earth attracts objects	F = Gm₁m₂/r²
Frictional force (Frictional Force)	A force resisting motion	Helping walk on the floor	f = μN
default key (Normal Force)	A force perpendicular to the base	Carrying a desk book	N = mg (available base)
traction (Tension Force)	Force acting through the rope	Lifting weights with a pulley	T
Centripetal force (Centripetal Force)	towards the center in a circular motion	Spinning stone, planets	F = mv²/r
Centrifugal force (Centrifugal Force)	Out of Center (Dummy Key)	Leaning out on the bus ramp	F = mv²/r

🔄 Friction

Types of friction

Type	Explanation	Size
Level friction(Static)	When the object stops	More 💪
Operating friction(Kinetic)	When the object moves	less
Rolling friction(Rolling)	As the object rolls	Very few ⚡

🎯 Friction Advantages-Disadvantages

Benefits ✅
Helps to walk 🚶 Assists in parking 🚗 Helps to write ✏️ Helps to climb the ladder 🪜 Helps to catch things ✋
Disadvantages ❌
Depreciation of mechanical parts 🔧 Heat will generate 🔥 Energy is wasted Slow down 🐢

🌍 Gravitational acceleration (g) variation

Place	value of g	The reason
At the poles	Most (9.83)	Near the center because the earth is flat
At the equator	Decrease (9.78)	The center is distant because the earth is salty
in height	decrease	Far from the center
in depth	decrease	The mass above does not attract
In the center	0 (zero)	Equal gravity in all directions

⚖️ Mass vs Weight

Mass	Weight
The amount of matter in the material	Earth's gravity
Nothing will change	Varies according to location
Unit: kg	Unit: N (Newton)
scalar quantity	vector size
Formula: m	Formula: W = mg

🎯 Mechanics - Master Shortcut Chart

📊 Newton's Laws - Quick Reference

fate	Name	Formula/Comment	example
1st	Physical law	Resistance to change of position	Leaning when the bus stops
2nd	Law of force	F = ma	Difficulty pushing a heavy object
3rd	Law of reaction	Action = Reaction	Rocket Flight 🚀

📐 Equations of Motion - Quick Reference

Eq	Don't know what?	remember
v = u + at	s	"VUA T"
s = ut + ½at²	v	"SUT half AT square"
v² = u² + 2as	t	"V square U square 2AS"

🔢 Memorize important numbers

Detail	value	Trick
Gravitational Acceleration (g)	9.8 m/s² ≈ 10	"g = TEN"
g at the pole	9.83 m/s²	"Pole = More"
g at the equator	9.78 m/s²	"Equator = Less"
g at the Earth's center	0	"Center = Zero"
Newton's birth year	1642	-
Publication of Principia	1687	-

📝 Frequently asked MCQ

1.Another name for Newton's first law?
a) Force lawb) Physical Law ✅c) Law of reaction d) Law of momentum

2.Which rule is F = ma?
a) First ruleb) Second rule ✅c) Third Law d) Law of Gravitation

3.Rockets fly based on which rule?
a) First rule b) Second rulec) Third Rule ✅d) None

4.SI unit of momentum?
a) N b) Jc) kg·m/s ✅d) m/s²

5.What is the value of gravitational acceleration (g)?
a) 8.9 m/s²b) 9.8 m/s² ✅c) 10.8 m/s² d) 11.2 m/s²

6.The value of g being higher?
a) At the equatorb) At the pole ✅c) At the top of the hill d) At the center of the earth

7.Immortals in Rebound?
a) Momentum only b) Energy onlyc) Momentum and kinetic energy ✅d) Anything perishes

8.SI unit of force?
a) Newton ✅b) Dyne c) Joule d) Watt

9.Which has more friction?
a) Level friction ✅b) Kinetic friction c) Rolling friction d) All things being equal

10.Unit of mass?
a) kg ✅b) N c) m/s d) J

🎯 Final Memory Trick - "NEWTON"

N- Newton's 3 Laws
E- Equations: v=u+at, s=ut+½at², v²=u²+2as
W- Weight = mg (N), Mass = kg
T- Third law: Action = Reaction (Rocket)
O- One Force unit = Newton = kg·m/s²
N- Nine point eight = g (9.8 m/s²)

⚠️ Common Mistakes - Things to Avoid

❌ mass weight one → ✅Mass (kg) ≠ Weight (N)

❌ g does not change anywhere → ✅g varies with location

❌ Momentum is destroyed in collision → ✅Momentum never dies

❌ Centrifugal force Real force → ✅Pseudo force

❌ Rolling friction is high → ✅Position Friction > Run > Scroll

📐 formula summary

key	F = ma	N
Weight	W = mg	N
momentum	p = mv	kg·m/s
Friction	f = μN	N
Centripetal force	F = mv²/r	N
Earth's gravity	F = Gm₁m₂/r²	N

🏆 Remember - "123"

1st Law:Inertia - Resistance to change of state
2nd Law:F = ma - force = mass × acceleration
3rd Law:Action = Reaction - Rocket, Walk, Swim

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