# Work and Energy Work and energy Work vs

• Slides: 12

Work and Energy • • • Work and energy Work vs. energy Work definition 2 important points about work Work and energy examples

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 Definition • Definition F. x. cos(θ) F x • Cos(θ) extracts F and x working together – +1 when together – – – -1 when opposed -1 to +1 when in between 0 when perpendicular • Work is a scalar quantity

Two important things • Total Work is – The work of the sum of all forces ΣFi x distance • or – The sum of the individual works of all forces. Σ(Fi x distancei) • Individual Work is – Force component in direction of displacement. • or – Displacement component in direction of force.

Examples of Work and Energy • • • Example 6. 4 – Work to increase car speed Example 6. 5 – Work to stop car Example - Work of Moon going around Earth Problem 23 - Air resistance on baseball Example 6. 8 – Falling baseball – Use 2 nd law – Use work • Example 6 -9 - Roller coaster – Use work – Couldn’t do easily by 2 nd law! • Vertical circle example (use work) • Note how you “mix up” dimensions!

Examples of Work and Energy - I •

Examples of Work and Energy - II •

Examples of Work and Energy III •

Examples of Work and Energy IV • vo v

Examples of Work and Energy V •

Work/Energy advantage • Work done my gravity This is the path the ball takes But this is the path you can use for calculating the work! • And the string tension does no work!