Work by Constant Force
W = Fd cosθ — see the horizontal component pull the block while F is applied at angle θ.
Key Notes
Work done by a constant force F over displacement d is W = F·d·cos θ, where θ is the angle between F and d.
Units: joule (J) = N·m. 1 J = work done by 1 N over 1 m parallel.
Scalar quantity. Can be positive (force along motion), negative (force opposite motion), or zero (force ⊥ motion).
Force perpendicular to displacement does NO work — even though force is exerted.
Gravity does NEGATIVE work when lifting up (F downward, motion upward).
Friction (kinetic) generally does negative work on the moving object — opposes motion.
Vector form: W = F · d (dot product). For non-constant F: integrate.
Work is a TRANSFER of energy — equal to change in KE when only F acts.
Formulas
Work (constant F, straight-line motion)
Scalar (dot) product of force and displacement vectors.
Positive / negative work
Sign of work depends on alignment.
Gravity (h drop)
Always +mgh if falling distance h.
Spring (constant compression)
F_spring is restoring; depends on x.
Important Points
Work is a SCALAR. Don't confuse direction with sign.
Force perpendicular to motion does NO work — centripetal force, normal force on horizontal surface.
Negative work means the agent is REMOVING energy from the body.
Hold a heavy bag stationary: you exert force but distance = 0 ⇒ W = 0 (physics definition). Different from biological 'effort'.
Work depends on the PATH ONLY for non-conservative forces (friction). For conservative forces (gravity, spring), work depends only on endpoints.
Conservation of energy: W_net = ΔKE (work-energy theorem).
Work by Constant Force notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.