Science Study Guide

Science Study Guide

Energy, Forces, and Motion

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Student Expectations

The student is expected to identify and explain different forms of energy, including mechanical, light, sound, and heat/thermal in everyday life.

The student is expected to demonstrate and observe how position and motion can be changed by pushing and pulling objects to show work being done, such as swings, balls, pulleys, and wagons.

Key Concepts

• Mechanical, light, sound, and heat/thermal energy are useful in everyday life.
• Heat energy helps cook food and keeps us warm in winter, while mechanical energy is associated with movement.
• Light and sound energy help us communicate and share information.

·       Pushing and pulling can cause an object to change position and to move.

·       Work happens when a force is used to move an object over a distance.

·       Tools such as swings, balls, pulleys, and wagons can be used to help move objects.

Fundamental Questions

• What is mechanical energy and how do we use it?
• What is heat energy and how do we use it?
• What is light energy and how do we use it?
• What is sound energy and how do we use it?

·       How can we cause an object to change position and to move?

·       What is work?

·       What tools can we use to show work is being done?

Explanation:

Understanding how work is done when force changes the position and motion of objects plays an important role in preparing students for fifth grade when they design their own force experiments.

Key Concept 1: Pushing and pulling can cause an object to change position and to move.

A force is a push or pull that causes an object to move, stop, or change direction. People, objects, or nature can pull or push an object. A catcher stopping a thrown baseball, a bulldozer pushing dirt, or the wind pushing leaves over a field are examples of pushing forces. A mother pulling on a toddler’s arm to stop the child from running, a tow truck pulling a car out of a ditch, or gravity pulling water down are examples of pulling forces that stop, move, and change directions of objects. A magnet can pull certain metal objects. Friction can pull on objects and slow them down.

Key Concept 2: Work happens when a force is used to move an object over a distance.

Several hundred years ago, Sir Isaac Newton, a British scientist, figured out some rules about how objects move. He concluded that the bigger the mass of an object, the bigger the force needed to move the object. The smaller the mass of an object, the smaller the force needed to move the object.

For example, it takes more force to move a car than to move a toy car. Scientists after Newton added another idea about force: to do work requires force, but the force exerted has to actually move an object. Most people think if any effort is exerted, then work is done. The scientists definition of work is different than the common meaning for work. For a scientist, work is done only if a force moves an object across a particular distance. If you try to push a car and it does not move, then no work has been done on the car. You might have exerted effort and ended up sweating trying to move the car, but the car did not budge and no distance was traveled; hence, no work was done on it.

Key Concept 3: Tools, such as swings, balls, pulleys, and wagons, can be used to help move objects.

A swing is actually a pendulum that goes back and forth. Students can brainstorm how to make a pendulum game with a weight on a string to see who can propel (push) a small object the farthest. Games with balls that push objects, such as bowling, can be constructed on a small scale in the classroom to explore moving objects with a rolling ball. Pulleys can be made from a string looped over a pencil. Students can attach paper cups as a holder to raise objects to determine the greatest number of small objects that can be lifted to a certain height in a prescribed amount of time. Drawings or measurements can be made of the movement of the objects in each of these games to emphasize that work was done across a certain distance.

Energy is what is needed to do work or cause change. Students had prior experience in the first grade identifying and discussing how different forms of energy, such as light, heat, and sound, are important to everyday life; and in the second grade investigating the effects on an object by increasing or decreasing amounts of light, heat, and sound energy, such as how the color of an object appears different in dimmer light or how heat melts butter. Third grade students will expand their understanding of energy by adding the term mechanical energy (energy from movement or the potential to do movement) and the term thermal energy (the internal energy of a substance due to the movement of the tiny particles within it, measured as temperature and often called heat). Chemical and nuclear forms of energy are studied in later grades. The emphasis in third grade is on the usefulness of energy forms in daily life.

Key Concept 1: Mechanical, light, sound, and heat/thermal energy are useful in everyday life.

Mechanical energy is the energy of moving objects (kinetic energy), like a skateboarder rolling down a ramp, and energy which is stored (potential energy), like the skateboarder getting ready to move at the top of the ramp. However, in third grade, mechanical energy focuses only on the energy of moving objects (kinetic energy), not stored energy.

Light energy comes from the Sun, other stars, light bulbs, matches, and glow-worms, which give off their own light that travels in straight lines to our eyes. We see all other objects, such as a ball or flower, because light is reflected off their surfaces to our eyes when we are looking at the objects.

Sound energy is produced by vibrating objects. Although sound is detected by the ear, students can feel sound vibrations when they touch their throats while talking or see sound vibrations when they put a paper plate or some candy sprinkles on top of a loud radio that causes the sprinkles to bounce around. Sound is produced in nature when animals make sounds, the oceans pound the shores, and the wind blows through the trees. Sound is also produced by vibrating objects, such as musical instruments, radios, and moving machines.

Thermal energy is the kinetic energy of the atoms/molecules in a substance. Heat is the transfer of thermal energy between substances, from hotter to colder substances. For third graders, heat energy and thermal energy are interchangeable. When molecules of a substance move faster from absorbing heat, thermal energy increases causing the temperature to rise. Third graders will explore how uses of mechanical, light, sound, and heat/thermal energy have impacted the world.

Key Concept 2: Heat/thermal energy helps cook food and keeps us warm in winter, while mechanical energy is associated with movement.

Early humans used thermal energy by adding layers of fur or building bigger fires to keep warm when winter came. Today, elaborate furnaces or solar energy panels provide thermal energy for buildings, and modern insulated synthetic fabrics provide the warmth that our bodies need. Before stoves and ovens were invented, food was cooked over an open fire. Unless families are camping, most food is cooked on modern electric or gas stoves. Thermal energy in toasters, barbeque grills, coffee pots, and microwave ovens heats the things we eat. Cooking food with heat energy has become a billion dollar business with computerized, automated ovens.

Machines, people, or animals in action, the wind, and flowing rivers are all examples of things moving due to mechanical energy. Humans have invented ways of using mechanical energy for work and play. Millions of years ago, ancient man moved a rock swiftly down toward another rock to chip away pieces to form a pointed, stone knife.

Today, we no longer use stone tools to produce knives; factories with automated sharpening machines produce thousands of fine-bladed metal knives. Long ago, farmers cut crops with a single blade. Today, farmers drive enormous machines (combines) to harvest wheat. From the spinning clothes dryer, to the pencil sharpener, to farm machinery, we depend on mechanical energy to do work and change things for us at home, school, and work.

Key Concept 3: Light and sound energy help communicate and share information.

In past ages, humans used burning wood, oil lanterns, or candles to give off light energy inside or outside when it was dark. Today, with the invention of the light bulb, our world continues to function when it is night. From desk lamps for reading to neon signs for baseball field scoreboards, humans can work and play at night by using light energy. Astronomers use light gathered by a telescope from distant stars or reflected off celestial bodies to share information about space. Light from televisions communicates the news or entertains us with shows. Light from overhead projectors communicate school subject information. Barcode scanners, computer screens, and stoplights are also examples of how light changes things or makes work easier. In later grades, students will learn about forms of invisible light that are useful, such as microwaves, radio, radar, ultraviolet, X-ray, etc. For now, third graders will focus on the uses of visible light.

Over the ages, the use of sound energy from vibrating objects has changed from beating drums for passing messages in ancient times to modern audio devices like iPods and band amplifiers that can produce sound for one person or for thousands. Early phonographs recorded sound on wax tubes.

Today, sounds can be recorded on tape or digitally by using computer hardware and software. All audio devices, old and new, produce sound energy based on vibrations. Sound energy from musical instruments produces vibrations by variations of pounding, plucking, blowing, or strumming motions that cause distinct frequencies of sound waves to reach the ear as music. Students will explore uses of sound energy at school, home, and work.