Energy in a Roller Coaster Ride
Sixth Grade – Unit 1: Matter and Energy
Lesson adaptation by David Grams
*This lesson was adapted from a lesson from The Teachers' Domain Open Educational Science Resources Collection 2007, a collaborative production of WGBH Educational Productions, the WGBH Media Library, and WGBH Interactive, with major funding provided by The William and Flora Hewlett Foundation.
Goal:
Primary: Understand that objects in motion have kinetic energy and that objects have potential energy due to their relative positions. Energy may be changed from one form to another, but the amount of energy stays the same. (P.EN.06.11)
Background:
The law of conservation of energy states that within a closed system, energy can change form, but it cannot be created or destroyed. In other words, the total amount of energy remains constant. On a roller coaster, energy changes from potential to kinetic energy and back again many times over the course of a ride.
Kinetic energy is energy that an object has as a result of its motion. All moving objects possess kinetic energy, which is determined by the mass and speed of the object. Potential energy is the energy an object has as a result of its position. Potential energy is stored energy that has not yet been released. Gravitational potential energy is potential energy that results from an object's position in a gravitational field, and is equal to the object's weight multiplied by its height.
For most roller coasters, the gravitational potential energy of the cars at the peak of the first hill determines the total amount of energy that is available for the rest of the ride. Traditionally, the coaster cars are pulled up the first hill by a chain; as the cars climb, they gain potential energy. At the top of the hill, the cars have a great deal of gravitational potential energy, equal to the cars' weight multiplied by the height of the hill. When the cars are released from the chain and begin coasting down the hill, potential energy transforms into kinetic energy until they reach the bottom of the hill. As the cars ascend the next hill, some kinetic energy is transformed back into potential energy. Then, when the cars descend this hill, potential energy is again changed to kinetic energy. This conversion between potential and kinetic energy continues throughout the ride.
In reality, the conversion between potential and kinetic energy (both are forms of mechanical energy) is not perfect. The force of friction acts on the moving cars, decreasing the total amount of mechanical energy in the system. The mechanical energy is not lost, however. It is transformed into thermal energy, which can be detected as an increase in the temperature of the roller coaster's track and car wheels. Because of friction between the coaster cars and the track (not to mention air resistance as the cars move forward at great speed), the amount of mechanical energy available decreases throughout the ride, and that is why the first hill of a roller coaster must always be the tallest.
Vocabulary:
Energy transfer
Potential energy (gravitational)
Kinetic energy
Materials:
* Bowling ball
* Marbles
* Tape
* Foam tubes for insulating ¾-1” water pipes, cut lengthwise in half (or)
* Poster board cut into approximately 18” x 4” strips
(Optional)
* Access to a data projector, computer, & Internet access
Procedure:
1) Have students read the Student Handout (Energy) at the end of this document. 2) Ask students to explain the difference between potential and kinetic energy.
2) Reinforce this difference by citing the example of someone standing at the top of a hill with their sled. Ask students where kinetic and potential energy are at their greatest.
3) Further reinforce the concept that potential energy increases as an object is moved higher ask a student volunteer to cup their hands then drop the bowling ball into their hands from a distance of approximately 1”. Ask a second “brave” volunteer if they would be willing to catch the bowling ball, but this time raise the ball as high as you can above the students cupped hands. (But don’t drop it!) Next, ask the class in which position did the ball have more potential energy and why. Students could discuss with a neighbor how they could test this hypothesis.
4) Ask students to think of at least one other example from everyday life where potential energy is transformed into kinetic energy, or vice versa. Allow students time to share their ideas among their peers then draw and label a diagram that illustrates the transformation.
5) Have students explore gravitational potential energy and kinetic energy by working in small groups to create their own rollercoaster using foam insulating tubes that have been cut lengthwise in half or sections of poster board. In both cases, tape can be used to attach overlapping sections. Examples of student-made “roller coasters” are available on the Internet and on the Teacher’s Domain website (Requires a free login).
6) When students are done have themdraw a picture of their rollercoaster and identify where each type of energy occurs. Remind students that the total energy of the system as the sum of both the potential and kinetic energies.
7) If the necessary equipment is available, show students the roller coaster interactive located on Teacher’s Domain website
8) Tell students that the pie chart represents the total amount of potential and kinetic energy in the system. Ask them, “What are the cars doing as the section representing kinetic energy increases in size?” Where is the potential energy greatest and least?
9)Play the interactive, first at full speed, by clicking on the "play" button and focusing on the graph depicting how the forms of energy change as the coaster cars move along the track, and then in step form to view the motion in detail.
10)Discuss the interactive activity with students, reinforcing the concepts of kinetic and potential energy. How do the predictions they made in their journals compare with what the activity is showing them?
11) Optional: In real life, not all of the potential energy of the coaster cars is converted to kinetic energy and back again; some mechanical energy is converted to thermal energy. Ask students why all that follow the first hill of a roller coaster are usually progressively smaller. Ask them if this is necessary? If energy wasn’t “lost” where could it have gone? Describe how mechanical energy gets converted to thermal energy along the track and the affects of friction. A good interactive website that allows students to control these variables is
Assessment:
Use both the drawings of the roller coasters students create and discussions to assess student learning.
(Student Handout)
What Is Energy?
What is always present but never visible? ENERGY! Energy is a difficult concept to understand because it is not a concrete object that you can see or touch. To understand what energy is, you must first understand what it does. That is, although energy isn’t visible, you can detect evidence of energy. Jumping, moving a wheelchair, eating, and singing all require energy. Nonliving things also use energy—a clock, vacuum cleaner, and mechanical toys all require energy to move. Work is involved whenever anything moves a distance, and energy is needed to do work. Therefore, energy is defined as the ability to do work.
Much like mass or volume, energy is a property of an object. It’s just that energy is more abstract than some other properties. Although energy itself isn’t visible, you can detect evidence of energy.
Movement, sound, heat, and light provide evidence that energy is present and being used.
Sound is produced when we strike something. But does sound do work? Yes, sound can move things. Sound waves move the tiny bones in your ears and shake windows when a loud truck passes by. Sound waves are also evident in the vibrations from playing a radio.
Our body is working even when it appears to be still. Breathing, blinking, and digesting food all require energy. For us to do these activities, our bodies burn the energy in food. We know this is happening because we feel warm (burning generates thermal energy, or heat). Therefore, heat is evidence that energy is being used.
If energy is the ability to do work, how does thermal energy fit into this definition? Thermal energy can melt an ice cube or make water boil. Therefore, the definition of energy can be amended to energy is the ability to do work or to organize or change matter.
Light is another observable form of energy. Light can change things. When light shines on your arm, it makes it feel warm. When light shines on a green plant, the plant can make food. Since energy is a property of matter, scientists have discovered ways to measure and quantify energy. Measuring energy helps to understand how it is used, how it changes forms, and how to increase energy efficiency.
Two Main Forms of Energy
In strict scientific terms, energy is classified into two main forms: kinetic and potentialenergy. Kinetic energy is defined as the energy of a moving object. A thrown football, aspeeding automobile, a waterfall, or a rock falling from a cliff is examples of objects thathave kinetic energy.
Potential energy appears in many different forms, and is defined as the energy in matter due to its position or the arrangement of its parts. The various forms of potential energyinclude gravitational potential energy, elastic potential energy, chemical potential energy,and electrical potential energy.
Potential Energy is often referred to as stored energy. Some scientists avoid the use of the word “stored” because it inaccurately depicts energy as a substance that is contained withina substance. In other words, some scientists and energy educators believe saying energy is“stored” is a misconception.
When something is lifted or suspended in air, work is done on the object against the pull of gravity. This work is converted to a form of potential energy called gravitational potential energy. When the item succumbs to the force of gravity, falling towards Earth like an apple from a tree, it converts potential energy into kinetic energy.