Force and Motion A Science A–Z Physical Series Word Count: 1,484 Written by Ron Fridell Visit www.sciencea-z.com www.sciencea-z.com KEY ELEMENTS USED IN THIS BOOK Force and The Big Idea: Force and motion are fundamental to all matter in the universe. A force is anything that can push or pull on an object. Forces influence objects that are at rest or that are already in motion. Isaac Newton’s three laws of motion involve inertia, mass, velocity, and Motion momentum. Key forces include gravity, friction, and magnetism. A force is required to do work, and generating a force requires energy. Energy can be stored as potential energy, or it can have kinetic energy—the energy of motion. Energy can also be converted and exchanged through energy transfer. Objects move in predictable ways. By learning about force and motion, we come to understand how using forces can produce motions that allow us to be safe and to enjoy ourselves. Key words: attract, direction, distance, electricity, electromagnetism, energy, energy transfer, engine, force, friction, gravity, heat energy, inertia, kinetic energy, law, lines of force, magnetism, mass, momentum, motion, potential energy, reaction, rest, sound energy, speed, velocity, weight, work Key comprehension skills: Cause and Effect Other suitable comprehension skills: Classify information; compare and contrast; elements of a genre; identify facts; interpret charts, graphs, and diagrams; main idea and details Key reading strategy: Visualize Other suitable reading strategies: Ask and answer questions; connect to prior knowledge; retell; summarize Photo Credits: Front cover: © Corbis; back cover: © James Steidl/Dreamstime.com; title page: © iStockphoto.com/ Latta Pictures; page 3: © iStockphoto.com/Scott Sharick; page 4: © iStockphoto.com/Kristian Sekulic; page 5 (top left): © iStockphoto.com/Kim Gunkel; page 5 (top right): © Pavel Siamionau/123RF; page 5 (bottom): © iStockphoto.com/Joshua Hodge Photography; page 6 (top): courtesy of NASA/ Dennis Sabo; page 6 (bottom): © iStockphoto.com/otisabi; page 7 (top), 22 (top): © Jupiterimages Corporation; page 7 (bottom): © Jean-Leon Huens/National Geographic Society/Corbis; page 8: © iStockphoto.com/Andreas Steinhart; page 9 (top): © iStockphoto.com/Marko Roeper; page 9 (bottom): © iStockphoto.com/Andrey Artykov; page 10 (main): © iStockphoto.com/Vernon Wiley; page 10 (inset): © Pavel Losevsky/123RF; page 11: © iStockphoto.com/Kenneth Sponsler; page 12: © iStockphoto.com/ ranplett; page 13 (top): © iStockphoto.com/Enrique Ramos Lopez; page 13 (bottom): © iStockphoto. com/Claudia Dewald; page 14: © iStockphoto.com/Craig Dingle; page 15: courtesy of NASA; page 16 (top left): © iStockphoto.com/Darren Mower; page 16 (top right): © iStockphoto.com/nullplus; page 16 (bottom): © iStockphoto.com/One Clear Vision; page 17 (top): © iStockphoto.com/Sarah Salmela; page 17 (bottom): © iStockphoto.com/Marzanna Syncerz; page 18: © 3desc/Dreamstime.com; page 19 (top): © iStockphoto.com/Billy Gadbury; page 20: © iStockphoto.com/Stephen Dumayne; page 21 (top): © Learning A–Z; page 22 (bottom left): © Rmarmion/Dreamstime.com; page 22 (bottom right): © iStockphoto.com/Linda Kloosterhof; page 23 (top): © iStockphoto.com/Simon Podgorsek; page 23 (bottom): © Andreas Weiss/Dreamstime.com; page 24: © iStockphoto.com/Iia Dukhnovska Illustration Credit: pages 12, 18, 19: © Learning A–Z; page 21 (bottom): Signe Nordin/© Learning A–Z Written by Ron Fridell Force and Motion © Learning A–Z. Written by Ron Fridell All rights reserved. www.sciencea-z.com www.sciencea-z.com Table of Contents ro ll spinning Introduction ....................................................... 4 i spinning p n spinning s spinning g l Motion Needs a Force ....................................... 5 i spinningri jumping th e ng The Laws of Motion .......................................... 7 Newton’s First Law of Motion ......................... 8 creeping Newton’s Second Law of Motion .................... 10 Introduction Newton’s Third Law of Motion ...................... 12 The words above tell about motion. They Types of Forces ................................................ 13 describe different ways things move. Motion Gravity ........................................................... 13 is all around you. There is even motion inside Friction ........................................................... 16 you. Your blood is moving right now. Magnetism ...................................................... 18 For every motion, there is a force. In this Force, Motion, and Work ................................ 20 book, you will learn about motion and the Energy ............................................................... 21 forces that make things move. Potential and Kinetic Energy ......................... 21 Energy Transfer .............................................. 23 Conclusion ....................................................... 24 Glossary ............................................................ 25 Index ................................................................. 26 3 4 Motion Needs a Force Machines can be a force. A huge engine You need a force to move something. can push a rocket into Lifting, pushing, and pulling are all forces. space. A small electric Where do forces come from? motor can turn the Sometimes the force comes from a blades of a fan or person. When you lift your books, power a toy car. you are the force. If you push a car, Nature is also a you are the force. If you pull a force. Breezes make rope to play tug-of-war, you leaves shake in the are the force. treetops. Ocean waves push make boats bob in the water. Earthquakes lift shake the ground. pull The outer layer of Earth is made of pieces called plates. Earth’s plates move in several ways. The force of these moving plates causes earthquakes. 5 6 The Laws of Motion Scientists have done tests A law is a rule that people must follow. But on motion for hundreds of in science, law has another meaning. A law explains how things in the world always work. years. British scientist Isaac Newton discovered the force we call gravity. You cannot Newton’s First Law of Motion see gravity. But it causes Isaac Newton is known for his three laws things to fall toward the ground. of motion. These laws explain how things move. The first law has two parts. Some people think that Newton discovered gravity when a falling apple hit him on the Part one says that an object at rest will not head. That’s not true. But Newton did notice move unless a force moves it. For example, that things always fell down toward the your bike will stay parked until something ground. He would watch closely and make moves it. notes. That is how he discovered gravity. Part two says that an object will keep SIR ISAAC NEWTON (1642–1727) Isaac Newton lived on a farm in England. Instead of farming, moving in the same he chose to study math and science. He made many way unless a new important discoveries. At age 27, Newton did tests on light. He was the first force changes how person to state that light was it moves. It will keep made up of all moving at the same Why is it important to wear the colors of the a seat belt? Think about rainbow. He is now speed and in the same Newton’s first law of motion. one of the most famous scientists direction. If you pedal of all time! your bike faster or turn, your bike will change speed or direction. If you brake, it will stop. 7 8 Inertia (in-ER-shuh) makes an object keep Newton’s Second Law of Motion doing what it is doing. An object at rest will Newton’s second law of motion has to not move unless a force moves it. An object’s do with mass and speed. Mass is the amount motion will not change unless a force stops of matter, or physical stuff, in an object. For it or changes its speed or direction. Newton’s example, a huge boulder has a lot more mass first law of motion is also called the law than a tiny pebble. of inertia. This law says that an object’s motion depends on how much mass it has and how much force is needed to move it. A boulder has more mass than a small rock, so more force would be needed to move it or to stop it from rolling. An object has inertia when it is at rest or moving. A force is needed to make the object move, stop, or change direction. 9 10 Newton’s Third Law of Motion Newton’s third law of motion says that every force or action has an equal and opposite reaction. So, if you lift a 9 kg (20 lb.) box, the box This train has a large mass and a high speed. This means it has pulls down with an equal a lot of momentum. It would take a very strong force to slow or stop this train! force of 9 kg (20 lbs.). The second law is also about speed. The This law helps you faster an object moves, the more speed it understand why a balloon full has, and the more force is needed to stop it. of air goes flying if you let it go before you tie it. Air rushes out Think about a train speeding down a track. the open end. An opposite force pushes It has a lot of mass and speed. So a strong on the far end. This opposite force makes force is needed to overcome its inertia and the balloon fly. make it stop. The force in a moving object is called B momentum. The more speed and mass an object has, the more momentum it has. A 1. Air rushes out the open end (arrow A). 2. An equal, opposite Velocity is an object’s speed in a certain direction. force pushes on the Scientists measure momentum by multiplying an far end of the balloon object’s mass by its velocity. (arrow B). mass x velocity = momentum 3. The balloon flies around the room! 11 12 Types of Forces Imagine standing next to a tall building. You and the building both have mass. So you You have read about how people, machines, both pull on each other because of gravity.