{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

PHYS_2014_Lecture_12

# PHYS_2014_Lecture_12 - Lecture 12 Energy and Work Energy...

This preview shows pages 1–8. Sign up to view the full content.

Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 1 Energy can be transformed from one form into the other and back again. θ M M h M 0 U mgh K = = 2 0 1 2 U K mv = = 0 U mgh K = = A Pendulum transforms Gravitational Potential Energy to Kinetic Energy and back to Potential Energy Lecture 12: Energy and Work 2 2 1 1 2 2 i i f f mv mgy mv mgy + = + i i f f K U K U + = +

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 2 Energy depends on your Frame of Reference i.e. Energy is always measured relative to some chosen point. 20 m 10 m 0 m m =10kg 1960J g U mgh = = 980J g U mgh = = 0J g U mgh = =
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 3 s F c θ =90 ° How much work is done by the ball at the end of a string, moving in a circle around my hand? cos90 cos90 0 0 c W F s F s W = ⋅Δ = Δ = = ringoperator ringoperator arrowrightnosp arrowrightnosp Forces acting at right angles to the direction of motion do no work!

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 4 Conservative Force: a) The net work done in moving a mass between two points depends only on the location of the points relative to one another, not on the particular path followed. b) The net work done in moving a mass through any closed loop (round- trip) path is zero. 0 F ds = arrowrightnosp arrowrightnosp Nonconservative Force: The net work done in moving a mass between two points depends on the particular path, e.g. due to friction, drag, etc. Δ h Δ h °
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 5 Potential energy is always associated with a conservative force. Friction and Drag (air resistance) are examples of nonconservative forces . The energy lost (work done) by nonconservative forces is lost from the system...usually in the form of heat . The energy lost (work done) by conservative forces is still in the system and can be recovered. Conservative and Nonconservative Forces

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 6 A 50 kg ice skater is gliding along the ice, heading due north at 4.0 m/s. The ice has a small coefficient of static friction that prevents the skater from slipping sideways, but μ k =0. Suddenly, a wind from the northeast exerts a force of 4.0 N on the skater. a) Use work and energy to find the skater’s speed after gliding 100 m in this wind. b) What is the minimum value of μ s that allows her to continue moving straight north? w F arrowrightnosp f F arrowrightnosp s Δ arrowrightnosp y x v 1 m
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 12, Slide 7 a) The work/energy theorem can be written: 2 2 .

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}