Force and Motion Contact and noncontact forces Unit

Force and Motion Contact and non-contact forces Unit 1

Unit 2 Lesson 4 Types of Forces 3, 2, 1 Contact! What are some contact forces? • A contact force is a push or a pull on one object by another object that is touching it. • An applied force is a type of contact force in which one object directly pushes or pulls on another object. For example, in tug of war, you apply a pulling force to the rope. • A spring force (or elastic force) is the force exerted by a bending or stretching object on any object that is attached to it. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces What are some contact forces? • Friction is the force an object exerts on an object that moves across it. The force of friction tends to oppose the motion of the object. • Air resistance is a type of contact force that air exerts on moving objects. Like friction, air resistance tends to oppose the motion of an object. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces From a Distance What are some non-contact forces? • A force that pushes or pulls on an object without touching it is called a non-contact force. • A magnetic force is a non-contact force that exists between certain materials, such as magnetized iron. The force may be attractive (like a pull) or repulsive (like a push). Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces What are some non-contact forces? • An electrical force acts between objects that are electrically charged. It is a type of non-contact force. • Objects with like charges tend to repel (push) one another. Objects with unlike charges attract (pull) one another. • Gravitational force is a non-contact force of attraction that exists between any two objects that have mass. On Earth, we experience gravity as a downward force. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces Down to Earth What are gravity’s effects? • Gravity accelerates objects. • All objects on Earth fall at the same rate once air resistance and other factors are removed. • Force = mass × acceleration due to gravity (F = mg). On Earth, g is about 9. 8 m/s 2. • All matter has mass, so all matter is affected by gravity. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces What are gravity’s effects? • All objects experience gravitational attraction to all other objects. • Earth and other planets are round because of gravity. • Some objects in space are not round because they are too small for gravity to shape them into a sphere. • The paths of the planets, the sun, and our galaxy are determined by gravity. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces A Weighty Issue What determines the force of gravity? • The law of universal gravitation states that all objects attract each other through gravitational force. • The strength of the gravitational force is related to the mass of the objects and the distance between them. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 2 Lesson 4 Types of Forces What determines the force of gravity? • Gravitational force between two objects increases as the distance between their centers decreases. • Gravitational force between two objects increases as their masses increases. Copyright © Houghton Mifflin Harcourt Publishing Company