Transcript Chapter 10
Chapter 10 Forces 8th Grade Science Force • _______a push or a pull Force • One object exerts a _______ on another Force • Force is described by its ______ strength and by the direction ________ in which it acts • Example – if you ______ on a door, you exert a push Force in a different _______ direction than if you ____ _____ pull on the door. Static Friction • _____________ - the friction that acts on an Static Friction object that is not moving. • You must use________ Extra Force to start motion of a stationary object. • If you use a force that is less than force of ___________, then the object that is Static Friction stationary will not move. • Example: pushing a desk on the floor Sliding / Rolling Friction • ____________ Sliding Friction - occurs when two surfaces slide over each other. • Example: a ballet dancer puts sticky powder on the bottom of ballet shoes so that they do not slip on the floor. Rolling Friction • _____________ - when an object rolls across a surface • Example: skateboard – rolling friction acts in the _________ direction of the skateboards motion. opposite Fluid Friction • ___________ - occurs when a solid object Fluid Friction moves through a liquid. • Example: parts of a machine are bathed in oil so that they move smoothly over each other. • Example 2: a bike rider experiences fluid friction between the individual and the air. Pushed fluid aside fluid friction • When an object ____________, occurs Gravity • _______ Gravity - a force that pulls objects towards each other Isaac Newton - concluded that force acts to pull • __________ objects straight downward towards the center of the Earth. • Newton realized that ________ acts gravity everywhere in the _______, not just on Earth universe = ___________________ Law of Universal Gravitation Law of Universal Gravitation • Law of Universal Gravitation states that The force of gravity acts between all objects in the universe _____________________________________ • Any two objects in the universe, Without Exception _______________, attract each other. • We are attracted to the _______ and all the other Earth objects around us. • Objects all around us are _________ to us as well attracted – we don’t know it because the forces are small compared to the force of Earth’s attraction. Factors Affecting Gravity • Two factors that affect gravitational attraction between two objects are mass ____ and ________ distance • The more _____ mass an object has, the greater the Gravitational force ______________. Sun’s • Because the ______ mass is so great, it exerts a large gravitational force on the ________ planets distance • ________ - the farther the two objects are, the _________ the gravitational force lesser between the objects Weight and Mass • ________ - the measure of the amount of mass matter in an object • _________ - the measure of the gravitational weight force exerted on an object • When you step on a scale, you are determining the amount of gravitational force the Earth is exerting on you! • _________ varies but _______ does not Weight Mass Gravity and Motion • On Earth, gravity is a ________ downward force that affects all __ objects. • __________ - when the force of gravity is an Free Fall ____________ force, which causes the object Unbalanced accelerate to _________. • Near the surface of the Earth, the acceleration due to gravity is 9.8 _____ m/s - regardless of the object’s ______. mass Math / Analyzing the Data • Page 346 (1-4) Air Resistance Air Resistance • ____________ - fluid friction that objects encounter while falling through the air. upward • Air resistance is an _______ force that is exerted on an object falling _________. downward • Falling objects with a greater ____________ Surface area experience ______air resistance than objects more with less surface area. • Air resistance increases with ________ velocity Air Resistance Continued • As a falling object gains speed, ______________ increases also – eventually Air resistance the velocity of the falling object will be fast enough that the ________ force of air upward resistance is equal to the ________ downward force of Balanced force gravity = _______________ • When forces are ________ there is no balanced _________ acceleration - velocity remains constant Projectile Motion Terminal Velocity • __________________ - the greatest velocity of a falling object • ________ projectile - an object that is thrown • When a projectile is thrown at an ________ upward reduces angle, the force of gravity ________ its vertical velocity. • Eventually the ______ upward motion of the projectile will stop and ________ will pull it ________ gravity downward Section Assessment • Page 348 (1-3) Newton’s Laws • Newton proposed three basic laws of motion in the 1600’s • Newton’s first law restated Galileo’s _________ idea about force and motion. • Newton’s first law of motion states: An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force. 1st Law • An object that is not moving, will not move until a ___________. Force acts on it • If an object is moving, it will continue to move at a constant velocity until ________________ force acts to either _________________________ Change either speed or direction On Earth, ________ and _________ are gravity friction _______________ Unbalanced forces that often change an objects motion. Inertia inertia • _______ - is the tendency of an object to resist a change in motion - ______________ Galileo’s concept • Newton’s first law of motion is also called the _________. Law of inertia • Inertia explains why a person moves forward in their seat when a car stops suddenly. ________ moves you forward in your seat inertia while a seat belt ________________ Changes your direction Inertia depends on Mass greater mass • The _________ the _______ of an object, the __________ its inertia ______ and the _________ greater greater force Change its motion the ________ required to ______________. Second Law of Motion acceleration depends on an objects mass • _________ ________ and the ____________ acting on the object. Net force • Acceleration = Net Force Mass Acceleration Meters per second² • Acceleration is measured in _______________ • Mass is measured in __________ Kilograms (kg) • According to Newton’s Second Law – force is kg times m/s² = _____________ Newton (N) measured in __________ • ________ = SI unit of force Newton • Math Sample Problem on page 351 • Math Practice page 351 (1 and 2) Newton’s Third Law • To increase __________ you must either acceleration mass increase _____ force or decrease _____ • Newton’s Third Law states: if one object exerts a ________ on another object, then the force second object exerts a ________ of force _____________ in the ____________ Equal strength Opposite direction on the first object. • FOR EVERY ACTION THERE IS AN EQUAL BUT OPPOSITE REACTION Why don’t action and reaction forces cancel each other? • Read Examples on pages 354-355 Momentum • ____________ is a characteristic of a moving momentum object that is related to the mass and velocity of the object • Momentum of a moving object is calculated by __________________________ Multiplying mass times velocity (m x v) • The more momentum a moving object has, the more difficult its is to stop • Objects with greater ______ and ________ mass velocity have greater ____________ momentum Conservation of Momentum conservation • ____________ - conditions before and after an event • An amount that is conserved is the same amount ______ the event as it was ________ after before • The total amount of momentum objects have is _________ when they ________ conserved collide • Momentum can be __________ but not lost ____ transferred Law of Conservation of Momentum • _____________ Total Momentum of any group of objects remains the same, or is ___________, unless conserved Outside forces act on the objects. ___________ • Examples on page 358-359 - three different types of collisions Section Assessment • Page 359 (1-5)