1. Energetically Challenged Maximize your mousetrap potential

2. Re-cap Linear Forces: Friction – Proportional to Normal force – Static Friction opposes relative motion of two surfaces – Coefficients of friction found experimentally Rotational Forces: Torque – Torque causes angular motion – Moment of inertia found for drive axle T W mass W car N N N FsFs FsFs

3. Work and Energy You (120 lb) and a friend (150 lb) go hiking (uphill) after eating ½ of a pizza. –Who will use more energy as they are hiking? –Who will be able to hike farther (higher)? –Why do you make these predictions? What is the unit of energy that people track? How is this hiking example similar to your mousetrap car?

4. Work and Energy Your heavier ‘friend’ will use more energy: his weight (a force) is higher, so he will use more energy over the same distance. Because you and your friend start with the same amount of energy (calories from the ½ pizza), you will be able to go farther than your friend.

5. Energy: Potential and Kinetic Potential energy: an object at rest – Apple before falling from tree: – Mousetrap arm when trap is set: (calculated from transferred force) Kinetic energy: an object in motion – Apple falling from tree – Mousetrap car in motion

6. Putting it together Energy efficiency can be calculated, improved by analyzing work done by forces – Mousetrap arm – Friction – Torque

7. Max Your Ride Follow workbook to calculate efficiency of current model car Use what you know: past experiments – Propose improvements Troubleshoot, Redesign, Rebuild!