# Energy Transformation

In this unit, students focus on the science phenomena of the relationship between gravity and motion, tracing how gravitational potential energy transforms to kinetic energy in different energy systems. In this lesson, they investigate the relationship between the drop height of a bouncy ball and its rebound height. This page is a high-level extract of this lesson.

## Science Background for Teachers:

Science background provides teachers with more in-depth information on the phenomena students explore in this unit. Below is an excerpt from the science background information on energy transformation.

Isaac Newton was one of the first scientists to set forth the idea that gravity is a predictable force that acts on all matter. He also came up with three laws of motion, which we’ll explore a little later on. A force is a push or pull that acts on an object, changing its speed, direction, or shape. Gravity—the force of attraction between all matter—is one of the fundamental forces that governs the interaction of matter. It is believed to be caused by the warping of space and time in response to matter. Picture a bowling ball, representing a planet, sitting on a blanket that represents space. The warping of the blanket represents the object’s gravitational field. If you put an object with less mass on the blanket near the bowling ball, the object will fall into the depression of the bowling ball. Gravity works in the same way.

All matter has gravity, but the force of attraction depends on the mass of the two objects. Mass is the measure of the amount of matter that makes up an object or substance. It is measured in grams (g). The more massive an object is, the more its gravity will pull on other objects. Here on Earth, you always experience the pull of Earth’s gravity because Earth is so much more massive than anything else on the planet. Because of this, acceleration due to gravity is nearly identical everywhere on Earth (9.8 m/s^2). The force of gravity acting on an object is also its weight— a gravitational force exerted on an object by a planet or moon. It is measured in newtons (N). Here on Earth, the distinction between mass and weight is typically ignored by non-scientists because of gravity’s constant acceleration of 9.8 m/s^2. However, on other planets and the moon, which have different gravities, an object’s weight would change dramatically. For example, because the moon is less massive than Earth, its gravity is weaker than Earth’s, causing an object’s weight to drop by 83 percent on the moon compared to on Earth.

An object’s mass remains the same, but its weight changes depending on gravity. The object’s mass would remain the same regardless of where it was. Because gravity is an attractive force, objects don’t need to come into contact with one another to exert a force on each other. Instead, objects have gravitational fields, which are the area around the object where another object will feel the gravitational force of the first object. For example, Earth’s gravitational field extends beyond the atmosphere, pulling on all objects within it. This gravitational field causes patterns in movement. For example, every time you release a pen in the air, the pen will fall back to Earth’s surface because the pen is within Earth’s gravitational field.

As objects move within another object’s gravitational field, the energy within the field changes. Energy is the ability to do work. Work is any change in position, speed, or state of matter due to force. In other words, work is the transfer of energy by a force. Energy can either be stored or in motion. Energy that is stored is called potential energy. The energy of motion is called kinetic energy. Energy is never created or destroyed, but it can transform (change) from one form to another in an energy system. A system is a set of connected, interacting parts that form a more complex whole.

## Science Lesson: Exploring Energy Transformation

In this lesson students use the phenomenon of roller coasters to explore the relationship within an energy system between an object’s height above ground and the amount of potential energy stored in the system. Students develop and use models to support their analysis of the phenomenon.

## Science Big Ideas

• Gravity is an attractive force because it pulls objects together, rather than pushing them away, which is what opposing forces do.
• A system of objects may contain stored potential energy, depending on their positions relative to one another. A system is a set of connected, interacting parts that form a more complex whole. That potential energy can transform into kinetic energy that causes the objects to change their motion.
• Kinetic energy is energy in motion. Potential energy is energy that is stored.

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## Science Essential Questions

• What evidence is there that Earth’s gravitational force is pulling on everything on Earth’s surface?
• How does the force of gravity change the direction of a ball that is thrown up in the air?
• How is potential energy different from kinetic energy?
• Why do roller coaster cars need to be pulled to the top of the first hill, usually with a long chain that runs underneath the tracks?

## Common Science Misconceptions

Misconception: Gravity only exists on Earth.
Fact: Gravity is the force of attraction between all matter, which means that every object in the universe attracts every other object with its gravity.
Misconception: Energy can be created and destroyed.
Fact: Energy is never created or destroyed. Instead, it transfers from one form to another. When one part of a system loses energy, another part of the system gains energy, so the total amount of energy is always conserved.

## Science Vocabulary

Energy : the ability to do work

Force : a push or pull that acts on an object, changing its speed, direction, or shape

Gravitational Potential Energy : the energy stored in an object as a result of its vertical position or height above the ground

Gravity : the force of attraction between all matter; more massive objects have a stronger gravitational force

Kinetic Energy : energy of motion

Mass : a measure of the amount of matter that makes up an object or substance; measured in grams (g)

Potential Energy : energy that is stored

System : a set of connected, interacting parts that form a more complex whole

Weight : a gravitational force exerted on an object by a planet or moon; measured in newtons (N)

Work : any change in position, speed, or state of matter due to force

## Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

A 61-Meter Drop

In April 2018, an amusement park in Ohio called Cedar Point began testing its newest roller coaster. This roller coaster is called Steel Vengeance. A ride on Steel Vengeance will last about 2 minutes and 30 seconds. It will reach speeds of up to 119 kilometers per hour (74 miles per hour). The first drop is a 90- degree drop of 61 meters (200 feet).

The height of ice slides, waterslides, and roller coasters is key to how all of these rides work. The taller the ride, the faster you can go. This is because of gravity—the force of attraction between all matter (everything that has mass and takes up space). Gravity pulls objects together.

It’s gravity that keeps us and all objects on Earth from floating off into the atmosphere, and that pulls all objects thrown up in the air back to the ground. In fact, an informal motto for national roller coaster day, held every August 16, is, “May the force of gravity be with you.”

Understanding Gravity

All matter has gravity, from rocks to plants, animals, and stars. However, the force of attraction depends on the mass of the two objects. Mass is the measure of the amount of matter that makes up an object or substance. It is measured in grams (g). The more massive an object is, the more its gravity will pull on other objects.

Earth’s gravity pulls on all objects on or near Earth’s surface because Earth is so massive. Earth’s gravity pulls all objects near Earth’s surface downward. Gravity keeps you from floating off into space. Earth’s gravity is also what pulls you back to the ground from the top of a waterslide.

Weight and Mass

The gravitational force exerted on an object by a planet or moon is called weight. It is measured in newtons (N). Here on Earth, weight is calculated by multiplying the object’s mass by the acceleration of gravity. The acceleration due to gravity is nearly identical everywhere on Earth (9.8 m/s^2).

Non-scientists often think that an object’s weight is the same as its mass. The two are related because an object’s weight depends on its mass. However, weight also depends on the force of gravity. On other planets and the moon, which have noticeably different gravities, an object’s weight would change dramatically. For example, the moon is less massive than Earth. Because of this, its gravity is weaker than Earth’s, so an object’s weight would drop by 83 percent on the moon compared to on Earth. The object’s mass, on the other hand, would remain the same wherever it was.

Gravitational Fields

Because gravity is an attractive force, objects don’t need to come into contact with one another to exert a force on each other. Instead, objects have gravitational fields. A gravitational field is the area around one object where another object will feel the gravitational force of the first object.

For example, Earth is so massive that its gravitational field extends beyond the atmosphere, pulling on all objects within it, including the moon.

This gravitational field causes patterns in movement. Remember that a pattern is something that happens in a regular and repeated way. Every time you release a pen in the air, the pen will fall back to Earth’s surface because the pen is within Earth’s gravitational field.

## Hands-on Science Activity

For the hands-on activity of this lesson, students design an experiment to explore the relationship between the gravitational potential energy of a bouncy ball and its resulting bounce height (kinetic energy). Students collect and analyze data on the height the ball bounces when dropped from different heights, looking for patterns that might indicate a relationship between a ball’s height above the ground, the amount of energy stored in the system, and the ball’s resulting rebound motion.

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