Chapter 10

Section 1 – The Nature of Force Force - a push or pull Like velocity and acceleration, a force is described by its strength and by the direction in which it acts. SI unit Newton The combination of all forces acting on an object is called the net force. Chapter 10

Section 1 – The Nature of Force Unbalanced Forces - acting on an object will change the object’s motion Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion. Equal forces acting on one object in opposite directions are called balanced forces. Balanced Forces - acting on an object will not change the object’s motion Chapter 10

Section 2 – Friction and Gravity Friction - The force that two surfaces exerts on each other when they rub against each other. The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. Chapter 10

Section 2 – Friction (cont.) Types of friction Static Friction – Friction that acts on objects that are not moving sliding friction - objects slide against each other rolling friction - object is round or has wheels fluid friction - object moves through fluid (swimming) Is friction bad? ice, walking, car, bike Chapter 10

Section 2 – Gravity The force that pulls objects toward Earth Law of Universal Gravitation - The force of gravity acts between all objects in the universe. Too factors affect the gravitational attraction between objects: mass and distance. Mass - measure of the amount of matter in an object Inverse relationship between distance between object and their gravitaional pull Chapter 10

Section 2 – Gravity (cont.) Weight - measure of the force of gravity on an object Earth vs. Moon Weight (Newtons) = mass x 9.8m/sec2 Chapter 10

Section 2 - Gravity (cont.) Free fall - only gravity acting on the object (in a vacuum) In free fall, the force of gravity is an unbalnced force, which causes an object to accelerate. Acceleration due to Gravity = 9.8 m/s2 Air Resistance - Objects falling through the air experience a type of fluid friction Terminal velocity – The greatest velocity a falling object reaches air resistance forces balanced with gravity

Section 2 – Gravity (cont.) Projectile – An object that is thrown Projectile motion –throw object horizontally (football, soccer) Chapter 10

Section 3 – Newton’s First & Second Laws Newton’s First Law of Motion An object at rest will remain at rest, and an object that is moving at a constant velocity will continue moving at constant velocity, unless it is acted upon by an unbalanced force. Chapter 10

Section 3 – Newton’s First Law Inertia - the tendency of an object to resist a change in it’s motion Direct relationship between mass and inertia. (One can say that mass is a measure of an objects inertia.) Chapter 10

Section 3 – Newton’s Second Law Newton’s Second Law of Motion The acceleration of an object is directly proportional to force and inversely proportional to mass. Acceleration = Net Force/Mass Force = Mass x Acceleration F=ma Chapter 10

Section 3 – Newton’s Second Law Mass - the amount of matter in an object (SI units = kilogram (kg)) Force = Newtons (N), Mass=kilograms (kg), Acceleration = m/sec2 Sample Problems pg.351 Chapter 10

Section 4 – Newton’s Third Law (cont.) Newton’s Third Law of Motion If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. Chapter 10

Section 4 – Newton’s Third Law (cont.) Action-Reaction – pg. 354 Gymnast, kayaker, dog (Squid, skater, kick, walking) Action Reaction Pairs Motion? Forces cancel? Volleyball pg.355 Chapter 10

Section 4 – Momentum Newton called momentum an objects quantity of motion The momentum of a moving object can be determined by multiplying the object’s mass and velocity. Momentum = mass x velocity Sample problems pg.356 Chapter 10

Section 4 – Momentum (cont.) Law of Conservation of Momentum The total momentum of any group of objects remains the same (is conserved), unless outside forces act on the objects. Train examples - overheads pg.358 Chapter 10

Section 5 – Orbiting Satellites Rocket lift off - Newton’s third law - gasses expelled with a downward force, exert an equal but opposite force upward on the rocket. Satellite - any object that orbits another object in space centripetal force - any force that causes an object to move in a circular path Chapter 10

Section 5 – Orbiting Satellites (cont.) satellites in orbit around the Earth continually fall toward Earth, but because Earth is curved they travel around it pg.364 Satellite Motion Satellite location – LEO, Geo Synchronous Chapter 10

Chapter 10 Vocabulary gravity force Mass net force Weight inertia Free fall Air resistance Terminal velocity Projectile momentum conservation of momentum satellite centripetal force force net force inertia Newton’s first law Newton’s second law Newton’s third law Friction Static Friction Sliding Friction Rolling Friction Fluid Friction Chapter 10