Unit 7 - Energy

Unit notes here.

-Idea: Give lab practicum challenges at the beginning of units, but do them at the end. This unit you can hang on a mass on a spring and determine what height to drop it from to make it "kiss" an egg on the ground but not smash it.

The energy unit is developed similarly to the forces unit, with discussion of students' existing conceptions as a starting point. Energy is a very extensive and important topic- a large part of our household budgets are for it, there are wars related to it, etc.

-So what is energy? Start by listing student ideas on the board.

-Introduce the 1st Rule of Energy: All energy is stored. It must be stores some place (that we can name) and can "see."
-Questions that should be asked all unit:

• Where is the energy stored?
• Where did it come from?
• Where did it go?
• What does it do?

-Go back through the student list on the board and weed out which ones really are energy by seeing where the energy is stored:

• Waterfall- movement of water particles
• Solar- sun's atom/nucleus
• Nuclear- nucleus of atom
• ATP- molecule bonds
• Fuel- molecule bonds 
• Food- molecule bonds 
• Movement- movement of object
• Electric- electrons
• Heat 
• Potential 
• Light
• Sound

-Look at how/where energy is stored in a system with pie graphs? Key idea: there are not different forms of energy- it is all energy, just stored differently.

• Examples to consider: dune buggy/battery, car on a track pulled back against an elastic band, a dropper popper, etc. 
• What should be considered part of the system?
• What do the sizes of the pieces mean? Do they change over time? What does the size of the pie mean?

-Example: PHET energy skate park (has html5). How does changing different variables affect the charts?

-Deployment: Unit 7 Worksheet 1 - Energy Pie Charts.
Demo: Paper hit between 2" steel ball bearings to burn a hole in the paper, showing thermal energy from kinetic energy. 

-How do you see energy? How do you measure it? Is there a tool? -> Spring Lab - Don't make my springs wires!

• If I want to store energy in a spring or rubber band, what do I have to do?
• Is there anything we can measure here? -> Is there a relationship between the distance the spring is stretched and force? (Give each group different springs for this lab.)

-Analyzing Spring Lab data:

• All linear proportional relationship with zero as the y-intercept
• What do the different slopes show us? What do the slope units mean? What does it tell us about the spring? Do tighter or harder to stretch springs ("spring constant") have a bigger or smaller slope?
• But where is the energy in this data? Not slope, not equation… it's in the area under the line of the graph
• Equation discovered: Elastic energy = 1/2kx^2, measure in Joules or N*m

 

-New concept to add into systems- work is transferring energy into/out of a system.
 Deployment: Unit 7 Worksheet 3a - Qualitative Energy Bar Graphs

-Lab part 1: Car on a ramp pulled back against a rubber band

• What can I use to measure the energy of the car in different trials? What else can I measure about the car? 
• Research question: How does the energy (use F vs. d or spring constant) stored in the rubber band relate to the velocity of the car? (Have different groups use different masses.)
• Does the amount of energy in each trial stay the same? Do LOL bar graphs to show this
• Equation discovered: Kinetic energy = 1/2mv^2

-Lab part 2: What if we ramp the track now? 

• How does the energy stored in the rubber band relate to the height the car ends up at on the ramp? (Can use different masses and angles.)
• Does the amount of energy in each trial stay the same? Do LOL bar graphs to show this
• Equation discovered: Gravitational (potential) energy = mgh

-Lab part 3: What if I pull back a wooden block on a flat track? 

• How does the energy stored in the rubber band relate to the slide distance of the block? (Can have different groups use different masses and/or surfaces also.)
• Does the amount of energy in each trial stay the same? Do LOL bar graphs to show this
• Equation discovered: Work done by friction (area/energy) = Ff*d = umgd

-Deployment: Unit 7 Worksheet 3b - Quantitative Energy Bar Graphs

-Lab practicum idea: Try to get a mass suspended on a spring to just touch the top of an egg in a cup when released.