Energy and Friction Work and Energy Potential Energy

Energy and Friction • Work and Energy • Potential Energy – Gravitational – Elastic – Other • Modification for Frictional Loss • Examples Благовещенск, Россия Blagoveshchensk, Russia 2016 Oct 20

Work and Energy •

Work vs. Energy • Product of force, distance, and how they’re working together increases or decreases the magnitude of v. • How force and distance work together is very important. – If f and d inline, magnitude of v increases. – If f and d partially inline, magnitude of v increases a little. – If f and d perpendicular, magnitude of v remains constant. – If f and d partially opposed, magnitude of v decreases a little. – If f and d opposed, magnitude of v decreases. – If f but no d v remains constant.

Work and Energy •

Potential Energy •

Conservation of KE + PE •

Potential Energy • Without potential energy • With potential energy KE+PE • Don’t do both, or you’ll be double-counting! KE+PE

Forces and Work 1. Gravity (PE) 2. Elastic (PE) 3. Electrostatic (PE – next semester) 4. Molecular/ Nuclear (PE – take more physics) 5. Any other force whose work only depends on endpoints (PE) 6. Normal (Never does work) 7. Circular (Never does work) 8. Friction (Requires fudge factor) 9. Applied Forces (Requires fudge factor, or may not be appropriate for work/energy)

Friction and Energy • Work friction KE+PE

Examples

Example 1 •

Example 2 – Part A •

Example 2 – Part B •

Example 3 •

Example 4 •

Example 5 • Problem 56 Forces acting: elastic, normal, friction

Example (5 cont) •