Roller Coaster Dynamics 2: Energy Losses - 1

Transcription

1 Lab Safety Policies Don t stand on lab chairs Don t sit or stand on lab tables No dangling jewelry or loose clothes. No open toed shoes. Be careful with sharp corners. Recall location of phone and first-aid kit. Report ALL injuries 1

2 Overview of Labs Lab 1 Introduction to Roller Coaster Design Lab 2 Energy Losses Lab 3 Circuit Prototyping Lab 4 Speed Sensor Calibration Lab 5 Building Session #1 Lab 6 Building Session #2 Lab 7 Building Session #3 Lab 8 Final Construction - Preliminary Testing of Design Lab 9 Final Testing of Design Lab 10 Oral Presentations

3 Roller Coaster Dynamics 2: Energy Losses - 1

4 Recap of previous lab Law of Conservation of Energy Energy can neither be created nor destroyed Energy can transfer from one form to another Examples of Energy Losses are the following: Resistive forces, such as friction and air resistance Act on a body in motion and cause energy to be transferred to unwanted forms (i.e. heat). For the roller coaster ball, " "

5 Recap of physics reading module Friction is a process that results in a force that opposes an action. Static Friction (acts to prevent motion) Kinetic Friction (exists between moving surfaces) Sliding Friction (due to sliding action of the object) Rolling Friction (due to rolling action of the object) Friction causes your ball to lose energy as it traverses along the track.

6 Recap of physics reading module Slippage results from a steep angle causing the ball to slide rather than roll. Sliding friction is generally greater than rolling friction. Curved Motion Critical velocities: At the top of a loop: v gr At the top of a bump: v gr Bank angle creates the centripetal force needed to keep the ball on the track.

7 Agenda Day 1: Experiments to calculate rolling friction coefficient Experiments to calculate average G-force Day 2: Experiments to calculate static friction coefficient Working on post-lab data analysis

8 Roller Coaster Energy Analysis Spreadsheet You will be using a RC Energy Analysis Spreadsheet to model most, but not all of the energy losses that your coaster will experience. This Excel spreadsheet allows for Vertical loops/curves Bumps Horizontal loops/curves Relatively straight sections of track Energy losses due to friction, G-forces and air resistance are included.

9 Additional Energy Losses Snap-fit spacing - Too wide a spacing can cause excessive energy losses through track deformation. Structural stability (including track) - An unstable structure can cause energy losses through movements within the structure. Bending of the track can also cause energy losses. Differential forces between rails along horizontal curves The ball will exert a different amount of force on each rail of the track.

10 Lab Activities (Part 1) Lab Apparatus Circular Arc (Rolling Friction) Group Rotation Data will be collected at the front table by each team. Each team will take turns rotating to the table and collect data with one ball on a total of three apparatus. Each group will be notified when it is their turn to rotate to the front table. Each group should record their data on the printed worksheet at the front table and on the computer at the instructor s station.

11 Circular Arc Apparatus - Friction Ball is released at point A. A The type of motion (oscillation, simple harmonic motion) is a way to roll a ball a relatively large distance with a relatively small apparatus. Ball oscillates for some time and eventually comes to rest Why?

12 Lab Activities (Part 2) This activity will be done at your table during the entire lab period. Locate your sample build kit, speed sensors, Arduino board. Build the support structure and track. Take measurements for four cases. Analyze, graph, and discuss your results.

13 You'll make this support structure 13

14 Experimental Setup You'll add speed sensors at the beginning and end of the horizontal curve and measure the energy losses for different starting points. Sensor B Sensor A

15 Speed Measurement Accuracy Tests of production speed sensors show an accuracy of about +/- 2% when using a correction factor of This is with the LED and photo-transistor visually aligned. Visually confirm that the glued alignment of the two LEDs is correct. If not aligned, errors of up to 10% can occur!

16 Let s put things together! Energy losses on straight track: Frictional forces Air resistance Additional energy losses: Snap-fit spacing Structural stability Differential forces between rails A ball following a curved path: Involves centripetal force. Has different frictional losses than when rolling on straight track.

17 Assignments and Reminders The post-lab data analysis spreadsheet will be due at midnight next Friday for instructor to check your calculations. You will have some time to work on the data analysis in the lab session next week. If you can finish the calculation for circular arc and half-horizontal loop before the lab, the instructor can help your team check the results during the lab session.