bk1+2.3

III. Friction and Gravity A. Friction 1. The force that 1 surface exerts on another when 2 rub against each other. 2.Acts in a direction opposite to the object's direction of motion. 3. opposes motion. 4.eventually will cause an object to come to a stop. 5. Strength of the force of friction depends on 2 factors. i. type of surface involved. ii. how hard the surfaces push together. iii. rough surfaces produce greater friction than smooth surface. iv. Force of friction increase if the surfaces push harder against each other. 6. Different kinds i. sliding friction- solid surface slide over each other. ii. Rolling friction-objects roll over a surface. a.) force needed is less than sliding friction. iii.)fluid friction-when an object moves thru a fluid a. force needed is less than sliding friction.

2.3 QUIZ 1.TYPES OF SURFACE; How hard surfaces are pushed together 2. put oil on the surface 6.the force that one surface exerts on another when the 2 rub against each other 7.the kind of friction that results when a wheel turns on a surface. 8.the kind of friction that results when you rub sandpaper against wood 9. the kind of friction exists between oil and door 10.a measure of the force of gravity on an object 11. the state that exists when the only force acting on an object 12. a force that accelerates objects toward earth 13. a falling object reaches this when forces of gravity and air resistance are balanced 14. the kind of friction that slows a falling object

Study Guide 4. weight 5. in free fall 6. friction 7. weight 18.true 19. false - gravity 24. gravity 25. projectile

B.Gravity 1. The force that pulls objects toward Earth 2.Isaac Newton 3. Free fall - the only force acting on a falling object is gravity, Object is in free fall 4. Near Earth's surface - acceleration due to force of gravity is 9.8 m/sec 5. Every second velocity increases by 9.8 i accelerate at constant rate regardless of mass 6. Projectile - object is thrown i Object that is dropped or thrown horizontally is in free fall 7. Air resistance i Objects falling through air experience a type of fluid friction ii. upward force iii. not same for all objects iv. greater surface of area of an object greater resistance v. increases with velocity a.) falling object speeds up, air resistance increases vi. Eventually air resistance = force of gravity 8. Terminal Velocity - the greatest velocity the objects reaches 9. Weight - the force of gravity on a person or object at the surface of a planet i measure of the force of gravity on an object ii. mass in the measure of the amount of matter in that object iii. weight = mass x acceleration due to gravity C. Universal Gravity 1. Law of Universal Gravitation i. the force of gravity acts between all object in the universal ii. Sir Isaac Newton 2. Strength of the force depends on the masses of the objects involved 3. Also depends on distance between the objects i. farther apart - weaker force