USING INTEGRATION TO CALCULATE WORK, ENERGY, ETC
BASIC FORMULA WORK = (FORCE).(DISTANCE) ENERGY = CAPACITY TO DO WORK
NO ENERGY
Lots of energy
Example: Spring Spring stretched ---> Work done ---> Energy is stored (Elastic Potential Energy) Spring released ---> Energy is released ----> Spring can do work
Time to compute! What is the amount of work done when a spring with spring constant 10 is stretched 6 inches beyond its natural position? 60? 360? 5? 2.5?
Answer NONE OF THE ABOVE! Need to Integrate!! Why?
Why indeed? Force versus amount of Because the force acting at different positions of the spring is different! In fact it changes continuously If x is amount of stretch, Force = 10.x (here k = spring constant = 10) Force versus amount of stretch
Approximate calculation of work done This chart shows work done over intervals of 0.3 length. Example: Work done when the spring is stretched from 2.1 inches to 2.4 inches is approximately equal to (Force at 2.1 inches)(0.3) 10(2.1)(0.3) = 6.3 units Shown by brown column
Now for the exact answer Work= Lim ∑ (work done over n intervals) = = 180
Other forms of potential energy Potential energy stored in an object at a certain height above earth Potential energy in atoms
The Catenary The catenary is the shape taken by a chain (like in a suspension bridge such as golden gate bridge (actual shape is parabola)) or an elastic rope suspended between two poles The shape minimizes potential energy Segue alert