Introduction to Work
📚 What is Work in Physics?
🔹 Real-Life Example
When you push a heavy box across the floor, you’re doing work because you apply force and the box moves in the direction of that force. But if you push against a wall for hours, you do zero work in physics terms (even if you’re tired!) because there’s no displacement.
A weightlifter holding a heavy barbell above their head does no work while standing still — work is only done during the lifting motion.
📘 Work: Work is said to be done when a force causes displacement in the direction of the force.
Work depends on three main factors:
- Force applied (F)
- Displacement (d)
- Angle (θ) between the force and displacement
🧪 Important Physics Formulas
🔸 General Work Formula
W = F × d × cos θ
- W: Work done (in joules, J)
- F: Applied force (in newtons, N)
- d: Displacement (in meters, m)
- θ: Angle between force and displacement
🔸 Special Cases to Remember
- θ = 0°: cos 0° = 1 → Maximum work (W = F × d)
- θ = 90°: cos 90° = 0 → No work (W = 0)
- θ = 180°: cos 180° = -1 → Negative work (W = -F × d)
⚖️ Units of Work
- SI Unit: Joule (J) = N⋅m
- CGS Unit: erg = dyne⋅cm
- Conversion: 1 Joule = 10⁷ erg
🧠 Vector Concept (Advanced – Class 11 Preview)
Work is the dot product (also called scalar product) of force and displacement vectors:
W = F⃗ · d⃗ = |F||d|cos θ
This is why work is a scalar quantity, even though it’s calculated using two vectors.
✨ Summary
Zero Work: No displacement or force at 90° angle.
Work is only done when displacement occurs in the direction of applied force.
Positive Work: Force and displacement in same direction.
Negative Work: Force and displacement in opposite directions.