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Download Notes - Types of Forces (Chapter 2, Lesson 2)
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2-2 Notes - Types of Forces Gravity • Many types of ___________ act on objects. • ______________ is an attractive force between all objects that have _______ . • The ______ does not travel in a straight line because of the __________________ force of _____________ acting on it. The Law of Universal Gravitation • The Law of Universal Gravitation states that all objects with _______ are attracted to each other. • The magnitude of attraction depends on the ________ of each object and the ________________ between them. • The gravitational force becomes ___________ as either or both objects increase in mass. • The gravitational force becomes ___________ as the distance between the objects increases. Weight and Mass • Mass is the amount of ____________ in an object and does not change with ___________. • Weight is the ___________________ force on a object and changes with _____________. • Weight is a __________ and a ___________. • Weight changes with _____________ above Earth. Friction • Friction is a force that _________________ the movement between two ________________ in contact. • A book pushed across a table __________ down because of ________________. • Friction is an ___________________ force acting on the book to ________ it down. • Without friction, you could not ________ , drive, skate, etc. • Sometimes we want to ____________________ it. (cleats, surfboard wax) Static Friction • _________ friction is the force between two surfaces in contact that keeps them from sliding when a force is applied. • A __________ is applied to a heavy box, but the box doesn’t ____________. • The forces are _______________ , the force ______________ the box equals the force of ___________ friction pushing in the _________________ direction. Sliding Friction • When the force pushing on the box is ______________ than the maximum static friction force, the box begins to ___________. • The frictional force that acts on the ____________ box is called ______________ friction. • The book pushed across the table slows down because of ______________ friction. • Without sliding friction, the book would continue __________ without a force being applied. • Usually friction is present and an ___________________ force must be applied to keep an object moving. • When friction is greatly _________________ , objects move with nearly constant velocity without an applied _________________ . p. 85 Rolling & Fluid Friction • __________________ Friction – when an object rolls over a surface. • __________________ Friction – when an object moves through a _______ OR a __________ (a __________). Elastic Forces • An elastic force occurs when a material is _________________ or _________________ . • A diving board exerts an upward ______________ force on the diver when it is bent _________________ . • 2 types: ______________ and _____________________ . Tension Forces • A tension force is a ________________ force exerted by an object when it is ______________ , such as a _____________ __________ . Compression Forces • A compression force is a _______________ force exerted by a material when it is ____________ or _______________. • The size of the compression force exerted by a material is equal to the size of the force that ____________ the material. Normal Forces • A normal force is the force exerted by an object that is __________________to the surface of the object. • The _______ is exerting a ______________ force on the table, caused by _____________ . • The ___________ is exerting an ____________ normal force on the cup, caused by ____________________ . Review ____ 1. A(n) ____ force is the force exerted by an object that is perpendicular to the surface of the object. A. compression C. normal B. elastic D. tension ____ 2. Which force causes a rolling ball to slow down? A. sliding friction B. static friction C. normal force D. gravity ____ 3. The gravitational force between two objects ____ as ____ increases. A. increases; distance C. increases; velocity B. decreases; mass D. decreases; distance ____ 4. If a student pushes a book across a table with a force of 10 N and the force of friction is 2 N, what is the net force on the book? A. 0 N C. 8 N B. 2 N D. 12 N ____ 5. What balanced forces are acting on a book sliding across a table? A. gravity C. sliding friction, normal force, and gravity B. gravity and friction D. gravity and normal force 2-2 Notes - Types of Forces Gravity • Many types of forces act on objects. • Gravity is an attractive force between all objects that have mass. • The ball does not travel in a straight line because of the unbalance force of gravity acting on it. The Law of Universal Gravitation • The Law of Universal Gravitation states that all objects with mass are attracted to each other. • The magnitude of attraction depends on the mass of each object and the distance between them. • The gravitational force becomes stronger as either or both objects increase in mass. • The gravitational force becomes weaker as the distance between the objects increases. Weight and Mass • Mass is the amount of matter in an object and does not change with location. • Weight is the gravitational force on a object and changes with location. • Weight is a force and a vector. • Weight changes with height above Earth. Friction • Friction is a force that opposes the movement between two surfaces in contact. • A book pushed across a table slows down because of friction. • Friction is an unbalanced force acting on the book to slow it down. • Without friction, you could not walk, drive, skate, etc. • Sometimes we want to INCREASE it. (cleats, surfboard wax) Static Friction • Static friction is the force between two surfaces in contact that keeps them from sliding when a force is applied. • A force is applied to a heavy box, but the box doesn’t move. • The forces are balanced, the force pushing the box equals the force of static friction pushing in the opposite direction. Sliding Friction • When the force pushing on the box is larger than the maximum static friction force, the box begins to slide. • The frictional force that acts on the sliding box is called sliding friction. • The book pushed across the table slows down because of sliding friction. • Without sliding friction, the book would continue moving without a force being applied. • Usually friction is present and an unbalancing force must be applied to keep an object moving. • When friction is greatly reduced, objects move with nearly constant velocity without an applied force. Rolling & Fluid Friction • Rolling Friction – when an object rolls over a surface. • Fluid Friction – when an object moves through a gas OR a liquid (a fluid). Elastic Forces • An elastic force occurs when a material is stretched or compressed. • A diving board exerts an upward elastic force on the diver when it is bent downward. • 2 types: tension and compression. Tension Forces • A tension force is a pulling force exerted by an object when it is stretched, such as a rubber band. Compression Forces • A compression force is a pushing force exerted by a material when it is squeezed or compressed. • The size of the compression force exerted by a material is equal to the size of the force that compresses the material. Normal Forces • A normal force is the force exerted by an object that is perpendicular to the surface of the object. • The cup is exerting a downward force on the table, caused by gravity. • The table is exerting an upward normal force on the cup, caused by compression. Review (Answers: 1-C, 2-B, 3-D, 4-C, 5-D) ____ 1. A(n) ____ force is the force exerted by an object that is perpendicular to the surface of the object. A. compression C. normal B. elastic D. tension ____ 2. Which force causes a rolling ball to slow down? A. sliding friction B. static friction ____ 3. The gravitational force between two objects ____ as ____ increases. A. increases; distance C. increases; velocity B. decreases; mass D. decreases; distance ____ 4. If a student pushes a book across a table with a force of 10 N and the force of friction is 2 N, what is the net force on the book? A. 0 N C. 8 N B. 2 N D. 12 N ____ 5. What balanced forces are acting on a book sliding across a table? A. gravity C. sliding friction, normal force, and gravity B. gravity and friction D. gravity and normal force C. normal force D. gravity