02.3a - Stores and Transfers

02.3 - Work, Energy and Power

02.3b - Energy Model

02.3c - Elastic Potential Energy

02.3d - Efficiency of Systems

02.3e - Work Done on a System

02.3f - Power

02.3g - Why start with Energy?

Energy Pie Charts

Pull back car up a ramp

Download PDF HERE

Energy carriers (or pathways, or transfers)

mechanically (when a force moves through a distance) - Work
electrically (when a charge moves through a potential difference)
by heating (because of a temperature difference)
by radiation (e.g. light, microwaves, sound)

Energy Stores

chemical (e.g. fuel + oxygen)
Mechanical
1. kinetic (in a moving object)
2. gravitational (due to the position of an object in a gravitational field)
3. elastic (e.g. in a stretched or compressed spring)
thermal (in a warm object)
magnetic (in two separated magnets that are attracting, or repelling)
electrostatic (in two separated electric charges that are attracting, or repelling)
nuclear (released through radioactive decay, fission or fusion)

Working with Energy Pie Charts

Given each of the scenarios below,

Sketch the setup, labeling the appropriate points on your sketch
Identify the system
- What is in your system?
- Is your system isolated?
- What is the ground state of your system? (What position did you identify as zero?
- Should your pies change size?
Change the initial state of the system.
- How much and in what direction did you add a force to change the initial state of your system?
Draw Energy Pie Charts to describe the forms of energy present at 4-5 points in the motion of the object.
- The moment the object starts to move is t = 0 seconds
- Energies to consider:
  - Kinetic (does it have any velocity?)
  - Gravitational Potential (does the object have a measurable height?)
  - Elastic Potential (is an object being stretched or compressed?)
  - Thermal (Dissipated) (is there friction involved in the scenario?)
  - approximate percentages of each type of energy stored or transferred during the motion of the objects.
Comment on the Law of Conservation of Energy states that 'energy cannot be created nor destroyed' where does the usable energy go in each of the scenarios.
You will be given one scenario to present on your whiteboard.

rapidsave.com_different_ppl_different_k-ank29y70m0ia1.mp4

A. Energy Ramps

Compare the energies of the ball at the bottom of each ramp.

B. Mass on a Spring

C. Bouncing Ball

Bouncing Ball in SloMo

D. Pop Up Toys

E. Spring Cart

F. Vertically Launched Ball

G. Pendulum

Energy Pie Charts Resources:

Energy Concept Builders:

Check your email for assignment from The Physics Classroom Concept Builders
What's up (and down) with KE and PE?

Energy Ranking Tasks

Small change from the video that we will use in class:

E(diss) will be described as ΔTherm

Chemical and Thermal Stores and Transfers

No Variable Problem

Upon arriving at a small Alpine cabin and wanting to relax after a long (8hr) hike, you would like to carry the minimum amount of wood into the cabin to warm it to a comfortable temperature and boil a kettle of melted snow to make a pot of tea/coffee. There is a pile of uniform logs outside of the cabin and a wood burning stove in the cabin.

Can we distill a problem down to the essential info?
What is quantifiable?
All models are wrong...but some are useful. G.E. Box
Can you justify your answer?
How could you create a program that would do all of your calculations for you?
Rarely will you be called on to determine the number of logs to carry into a cabin. However, where are some situations where an engineer would need to determine the energy demands of a project?

Construct a variable map to illustrate the various variable and their relationship each other.
Identify realistic quantities for the variables you have chosen.
Based on your variable map, solve the problem of the amount of wood you would need to carry into the cabin.
Evaluate the reliability of your solution.