DAY 79 - Conservation of Energy
#Goals: SWBAT...
1. ... Memorize and use the mechanical energy equation
2. ... Apply a problem solving strategy to conservation of energy problems
3. ... solve conservation of energy problems
WARM-UP:
In our everyday world, it may not seem as if energy is conserved. A hockey puck eventually loses its kinetic energy and stops moving, even on smooth ice. A pendulum stops swinging after some time. Suppose you have a total of $50 in cash. One day, you count your money and discover that you are $3 short. Would you assume that the money just disappeared? You probably would try to remember whether you spent it, and you might even search for it. In other words, rather than giving up on the conservation of money, you would try to think of different places where it might have gone.
Scientists do the same thing as you would with lost money. Whenever they observe energy leaving a system, they look for new forms into which the energy could have been transferred.
1. Copy & fill in the blanks: This is because the total amount of energy in a system remains constant as long as the system is _______ and _________ from external forces. The law of conservation of energy states that in a closed, isolated system, energy can neither be created nor __________; rather, energy is conserved. Under these conditions, energy changes from one _____ to another while the total energy of the system remains constant.
2. Copy & fill in the blanks: ME = KE + ___
3. Imagine a system consisting of a 10.0-N ball and Earth. Suppose a 10.0N ball is released from 2.00 m above the ground, (ground level is the reference level).
4. Given that as you release the ball, the ball isn't yet moving, what is the KEi of the ball?
5. What is the PEi of the ball? (Solve for it)
6. As the ball falls, it loses potential energy and gains kinetic energy. When the ball is 1.00 m above Earth’s surface: PE = mgh = (10.0 N)(1.00 m) = 10.0 J. What is the ball's KE at this point? (Hint: use the mechanical energy equation to solve...)
CLASSWORK:
1. HW Review
2. Kinetic Energy Lecture/Notes:
3. Practice Problems pg 287 #1-3
HOMEWORK
Read lab and assigned book reading.
Complete Prediction/Prelim Questions 1-6
Link to Lab is HERE
CLASSWORK'
1. Energy Transfer
How is energy transferred in the following scenarios?
Think about 1/ how the object's velocity changes; 2/ how the object's height changes
Create two bar graphs for each scenario (one initial, one final) showing PEi KEi and PEf KEf
A. Roller Coaster (initial: top of the drop final: bottom of the drop)
https://youtu.be/t8JAXbS2Xec?t=1m30s
B. Skiing (Initial: top of ski run final: bottom of ski run)
https://www.youtube.com/watch?v=VNH80LL14Vw
C. Pendulum (initial: release point middle: lowest point high: highest point)
https://youtu.be/vX074Q4kP9k?t=41s
2. Problem Solving Strategies:
Review the diagram from our Conservation of Energy (COE) Lab on the board by the door
A. Sketch a copy of the diagram
B. In your notes, complete the problem solving strategies steps from pg 295
3. Working a COE problem together
http://www.flippingphysics.com/coe-problem.html
A. Copy the work and solution steps in your notes
B. Is our answer a velocity? Why or why not?
C. Why can't we use projectile motion (x & y components, etc) to solve this problem?
D. Extra credit: Are you sure we can't use projectile motion?
Practice Problems:
Do Example problem 2 (pg 296)
pg 297 15
HOMEWORK:
pg 297 15 & 16