Home

 

 

 

Molecules in Motion

http://www.ignitelearning.com/

 

ENERGY PROBLEMS

When work is done on or by a system

 

Approximately how much kinetic energy
does the green box acquire?

 

[ Flash ]

 

 

 

 

PE = Just under 600 Nm

 

 

Ex 1) An object slides across a horizontal table which changes its KE from 20 J to 18 J in 2 sec.
What work does the object do against friction?

 

 

Ex 1) An object slides across a horizontal table which changes its kinetic energy from 20 J to 18 J in 2 sec. What work does the object do against friction?

 

 

 

W = 2 J

 

 

**Work against friction increases
an object's Internal Energy** (makes it hotter)

Friction is a
nonconservative force
(doesn't store energy)

(can't get back)

 

 

 

 

Joule Paddle

Conservation of Energy

Harper's New Monthly Magazine, No. 231, August, 1869.

 

 

 

 

 

Joule Paddle
Penn State Schuylkill

 

 

 

 

 

 

Work Energy Relationship

 

The work done on or by a system

= ΔKE + ΔPE + Wf

 

Wf - work done against friction

 

 

 

 

If ΔPE of yellow box = 30 J,
how much work did the green box do on it?

[ Flash ]

 

 

 

 

 

 

 

Work done by the ball on the floor changes the ball's mechanical energy

 

 

 


When the WORK equation
 doesn't WORK,

Use an ENERGY equation.
When an ENERGY equation
 doesn't WORK,
 
Use the WORK equation

 

 

 



   

 

Enrichment

Superfluids

The strange behavior of liquid helium

BBC

Superfluid_helium.mpg

Superfluid_helium.wmv

 

 

 

ŠTony Mangiacapre., - All Rights Reserved [Home]
Established 1995
Use any material on this site (w/ attribution)