1. WORK (कार्य)

Scientific Definition: Work is done when a force produces displacement.

• If no displacement ($s=0$) $\rightarrow$ No Work Done! (e.g., pushing a wall).
• Formula (सूत्र):

Unit: Joule (J) or Nm. (1 J = 1N force moves object by 1m).

Types of Work:

• Positive (+ve): Force & disp. in same direction ($\theta = 0^\circ$).
• Negative (-ve): Force opposite to disp. (Friction) ($\theta = 180^\circ$).
• Zero (0): Force $\perp$ to disp. (e.g., Coolie carrying load).

2. ENERGY (ऊर्जा)

Def: The capacity to do work is Energy.

Unit: Same as Work = Joule ($J$).

A. Kinetic Energy (गतिज ऊर्जा):

Energy due to motion of an object.

$\uparrow$ Mass or $\uparrow$ Velocity = $\uparrow$ K.E.

B. Potential Energy (स्थितिज ऊर्जा):

Energy due to position or shape (e.g., stretched bow).

($h$ = height above ground, $g$ = gravity)

3. LAW OF CONSERVATION

ऊर्जा संरक्षण का नियम: Energy can neither be created nor destroyed, only transformed.

Total Energy = $E_k + E_p = \text{Constant}$.

e.g., Free fall of a stone: $PE \downarrow$ converts to $KE \uparrow$.

4. POWER (शक्ति)

Rate of doing work. “How fast work is done”.

$P = \frac{Work}{Time} = \frac{W}{t}$

Unit: Watt (W). 1 kilowatt (kW) = 1000 W.

Commercial Unit: 1 kWh = $3.6 \times 10^6 J$ (1 Unit electricity).