Work & Energy · Physics

Energy with Friction and Dissipative Forces

Real systems lose mechanical energy. Friction and drag do negative work and convert energy into thermal/internal forms.

This topic includes

Subtopics to master

Use energy methods even when mechanical energy is not conserved — by tracking work done by non-conservative forces.

Non-conservative work

Work Done by Friction

Kinetic friction often does negative work: \(W_f = -f_k d\) when friction opposes motion.

Energy accounting

Mechanical Energy Loss

With friction, \(K_i + U_i + W_{nc} = K_f + U_f\). Here \(W_{nc}\) is work by non-conservative forces.

Thermal

Thermal Energy Considerations

Mechanical energy becomes internal energy (heat). You can model this as \(E_\text{th} = -W_{nc}\) in simple cases.

Real-world modeling

Modeling Dissipative Systems

Apply energy accounting with friction/drag to realistic scenarios (ramps, brakes, rough tracks).

Practice

Practice & Exercises

Solve energy problems with friction, signs, and real-world constraints.

Bridge

From Energy Loss to Power

Once you can compute energy change, power tells you how fast energy is transferred or dissipated.