Here are easy and exam-focused notes on “Motion, Force and Energy” from the Science and Technology syllabus of BPSC and UPSC.
ये टॉपिक बहुत ही important है क्योंकि इससे हर साल questions आते हैं BPSC और UPSC दोनों में। Means आपको motion, force और energy का basic understanding होना चाहिए। चलो आसान भाषा में एक-एक करके समझते हैं।
1. Motion (गति)
Motion means जब कोई object अपनी position change करता है with respect to time, तब हम कहते हैं कि object motion में है।
Types of Motion (गति के प्रकार)
- Rectilinear Motion – जब object straight line में move करे।
Example: कार सीधी सड़क पर चल रही है। - Circular Motion – जब object किसी circle के path में चले।
Example: पंखा घूम रहा है। - Periodic Motion – जब कोई object बार-बार repeat करे एक fixed time में।
Example: Pendulum की motion।
Important Terms in Motion
- Distance – Total path covered (scalar quantity)
- Displacement – Shortest path from initial to final position (vector quantity)
- Speed – Distance/time
Speed = Distance / Time - Velocity – Displacement/time (has direction)
Velocity = Displacement / Time - Acceleration – Change in velocity/time
Acceleration = (Final Velocity – Initial Velocity) / Time
2. Force (बल)
Force means कोई भी ऐसा push या pull जो किसी object की state को change करे।
Types of Force
- Contact Force – जब दो objects touch कर के force apply करें
Example: Friction, muscular force - Non-contact Force – बिना touch करे जो force लगे
Example: Gravitational force, magnetic force
Newton’s Laws of Motion
First Law – Law of Inertia
“कोई भी object अपनी rest या uniform motion में बना रहेगा जब तक कोई external force उस पर ना लगे।”
Second Law – Force = mass × acceleration
F = m × a
Means जितना ज्यादा force, उतनी ज्यादा acceleration।
Third Law – Every action has equal and opposite reaction.
Example: जब आप जमीन पर पैर मारते हो, तो जमीन भी उतना ही force लगाती है, जिससे आप ऊपर उछलते हो।
3. Energy (ऊर्जा)
Energy means ability to do work. Without energy, कोई भी काम possible नहीं है।
Types of Energy
- Kinetic Energy (KE) – जब कोई object move करता है, तब उसमें kinetic energy होती है।
KE = ½ mv²
m = mass, v = velocity - Potential Energy (PE) – जब कोई object किसी height पर होता है
PE = mgh
m = mass, g = gravity, h = height - Mechanical Energy – KE + PE
Total energy due to motion and position - Other forms – Chemical energy, Electrical energy, Thermal energy, Nuclear energy
Law of Conservation of Energy
“Energy can neither be created nor destroyed. It only changes from one form to another.”
Example: पंखा चलाने में electrical energy → mechanical energy में convert होती है।
Work
Work is said to be done when a force is applied and object moves.Work = Force × Displacement × cos(θ)
- अगर θ = 0°, Work = Maximum
- अगर θ = 90°, Work = 0
Unit of work = Joule (J)
1 Joule = 1 Newton × 1 meter
Power and Energy
- Power – Work done per unit time
Power = Work / Time
Unit = Watt (W) - 1 Kilowatt = 1000 Watts
- Energy – Total work done
Commercial unit = kilowatt-hour (kWh)1 kWh = 3.6 × 10⁶ J
Numerical Example:
Question:
A body of mass 2 kg is moving with velocity 4 m/s. Find its kinetic energy.
Solution:
KE = ½ mv²
= ½ × 2 × (4)² = 1 × 16 = 16 Joules
Quick Revision Points
- Rest means no motion, Motion means position change with time
- Newton’s laws are very important
- Kinetic energy = motion में energy
- Potential energy = height वाली energy
- Energy हमेशा conserved रहती है
- Force = push or pull
- Work = force × displacement
- Power = Work / time