PhysicsQuest

CONSERVATION OF ENERGY

INTRODUCTION

You are in Six Flags over Texas waiting  in line to try Batman the Ride roller coaster.

You boarded the roller coaster and now you're barreling down the track at 60 miles per hour, taking hairpin turns and completing death-defying loops.

Your heart is in your throat and your stomach is somewhere near your shoes! You are having so much fun!

Then you suddenly remember that the laws of PHYSICS are behind all the rides in the amusement park!

You've learned in class that the coaster has no engine. The car is pulled to the top of the first hill at the beginning of the ride, but after that, the coaster must complete the ride on its own. You aren't being propelled around the track by a motor or pulled by a hitch. The conversion of potential energy to kinetic energy is what drives the roller coaster, and all of the kinetic energy you need for the ride is present once the coaster descends the first hill.

In this PhysicsQuest  you will learn the principles of conservation of energy that allow you to enjoy fun and safe roller coaster rides. 

TASK

You will be given a series of questions and various links to Internet sites that will help you answer the questions.

By the end of this PhysicsQuest you will have a better understanding of the factors that have an effect on the total mechanical energy of an object.

PROCESS AND RESOURCES

Part I. INTERNAL vs. EXTERNAL FORCES

In class we distinguished between conservative and non-conservative forces. The author of this site categorizes these forces as internal and external.

1. What is the factor that determines the categorization of the forces?

2. Name three types of forces for each internal and external categories.

3. What happens to the total mechanical energy when an object is

   acted upon by  internal forces?

4. What happens to the total mechanical energy when an object is

   acted upon by external forces?

5. What determines whether an object does positive or negative work

   when acted upon by external forces?

6. What happens to the energy in the case of positive work? What

   happens to the energy in the case of negative work?

Part II. PROBLEM SOLUTION STRATEGIES

Go to the bottom of the page and read the paragraph right before the PRACTICE EXERCISES.

7. Write three questions that you should ask yourself before

   attempting to solve a problem involving conservation of

   energy?

Part III. BAR CHART ILLUSTRATIONS

8. What is a work-energy-bar chart?

9. What does the length of the bar represent?

Consider the example of a car which skids from a high speed to a stop across level ground with its brakes applied.

10. How many bars were constructed to illustrate this

     example? Which energies do the bars represent and why?

Consider now the example of a skier that starts from rest on top of hill A and skis into the valley and back up onto hill B.

11. What is the effect of using the ski poles?

12. How many bars were constructed and which energies are

     represented in the initial conditions?

13. How many bars were constructed and which energies are

     represented in the final conditions?

Part IV. STOPPING DISTANCE

Take a look at the animation depicting cars at three different speeds. You can observe that the red car is traveling twice as fast as the green car and that the blue car's speed is three times faster than the green car's speed.

14a. Which car has the greatest kinetic energy?

b. By looking at the work-energy-bar charts determine

   which car performs more work against friction?

c. What conclusion can be drawn regarding the stopping

   distance and the speed of the car?

Part V. ENERGY CONSERVATION IN ROLLER COASTERS

15. Explain in detail the energy transformation on a roller coaster.

     Be careful to use your own words.

16. How does the roller coaster illustrate the work-energy

     theorem, explain by using your own words.

17. Why is air resistance neglected when calculating energy

     transformations in roller coasters?

18. What can you say about the Total Mechanical Energy during

     a roller coaster ride?

Part VI. PROBLEMS

- This section should NOT be typed.

- Solve the following problems using only WORK/ENERGY

  equations.

- Include a simple sketch of each problem as appropriate.

- Show your work in every problem including:

  a. DATA

  b. EQUATIONS

- Solve problems: 4, 11, 13, 14 and 15.