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I. The First 2 Laws of Motion A. Newton’s Laws Sir Isaac Newton (1642–1727) able to state rules that describe the effects of forces on the motion of objects B. The First Law of Motion An object moving at a constant velocity keeps moving at that velocity unless an unbalanced net force acts on it (LAW OF INERTIA) C. Inertia & Mass --inertia-- the tendency of an object to resist any change in its motion - If object is moving it wants to keep moving - If object is at rest it wants to stay at rest UNLESS…… …UNBALANCED forces act on it! -The velocity of an object remains constant… UNLESS… …a force changes it! -The inertia of an object is related to its mass The greater the mass of an object the greater its inertia -- mass -- the amount of matter an object has -- weight -- the amount of mass PLUS the force of gravity acting on an object Force is calculated using units of m/s² AND kg (or g) these units combine into a unit called a NEWTON (mass + acceleration) D. The Second Law of Motion The acceleration of an object is in the same direction as the net force on the object Newton's 2nd Law of Motion Demo 1.) Force & Acceleration -Acceleration can be calculated from the following equation: Newton's Law's of Motion Song - Another Maaaaagic Triiiiangle! (*oooohhh…aaaaahhhh*) UNIT USED for FORCE: NEWTONS (N) Force = mass x acceleration REMEMBER: acceleration is the change in velocity divided by the time it takes for the change to occur HINT: Now for problems you may have to solve for acceleration first before dividing the force!!! 2.) Mass & Acceleration -The acceleration of an object depends on its mass as well as the force exerted on it - MASS vs. WEIGHT An object will always have the same MASS (amount of matter) no matter where that object is….Translation: MASS STAYS THE SAME! An object’s WEIGHT (mass + force of gravity) may be different in different places in the universe because of different forces of gravity…Translation: WEIGHT CAN CHANGE! Bill Nye: Mass vs. Weight & Momentum II. Gravity A. What is Gravity? -- gravity -- attractive force between any 2 objects depends on the masses of the objects & the distance between them Increasing mass increases an objects gravitational force! Decreasing distance between objects increases gravitational force! 1.) Gravity- A Basic Force The “Big 4” Basic Forces: GRAVITY ELECTROMAGNETIC FORCE STRONG NUCLEAR FORCE WEAK NUCLEAR FORCE B. Law of Universal Gravitation G universal gravitational constant d distance between two masses m1 & m2 the two masses TRANSLATION: Law of Universal Gravitation enables the force of gravity to be calculated between any 2 objects if their masses & the distance between them is known 1.) Range of Gravity - No matter how far apart 2 objects are, the gravitational force between them never completely goes to zero gravity is a LONG-RANGE FORCE Nye Tunes "G-R-A-V-I-T-Y" C. Earth’s Gravitational Acceleration - When all forces except gravity acting on a falling object can be ignored, the object is said to be in free fall -Close to Earth’s surface, the acceleration of a falling object in free fall 2 is about 9.8 m/s - Symbol for acceleration of gravity g -By Newton’s 2nd law of motion force of Earth’s gravity on a falling object = object’s mass times the acceleration of gravity… F = m x g UNIT USED = NEWTONS (N) 1.) Weight ***Weight is a force *** ***Mass is a measure of the amount of matter an object contains*** D. Weightlessness & Free Fall 1.) Floating in Space - If gravitational forces never disappear how does one become “weightless” (example: astronauts in space)? Objects will seem to float because they are all falling with the same acceleration astronaut & ship are falling towards Earth but falling at the SAME RATE Fun in Space- Zero Gravity - NASA footage E. Projectile Motion - Earth’s gravity causes projectiles to follow a curved path 1.) Horizontal & Vertical Motion -When you throw a ball force exerted pushes the ball forward to give it HORIZONTAL MOTION -Horizontal Velocity of ball is constant (*ignoring air resistance*) -When you let go of the ball, gravity pulls it downward giving it VERTICAL MOTION ball travels in a curve 2.) Horizontal & Vertical Distance -If a ball as thrown in a perfectly horizontal direction, would it take longer to reach the ground than a dropped a ball from the same height? NO!!! They would drop at the same time! Projectile Motion -Both balls travel the same vertical distance in the same amount of time thrown ball travels a longer horizontal distance F. Centripetal Force - When a ball enters a curve it is accelerating because its direction is changing (even if its speed does not change) Centripetal Force demo -When a ball goes around a curve change in the direction of the velocity is toward the center of the curve --centripetal acceleration-- acceleration toward the center of a curved or circular path --centripetal force-- net force exerted toward the center of a curved path 1.) Centripetal Force & Traction -A car rounds a curve on a highway centripetal force acts on the car to keep it moving in a curved path Centripetal Force is the frictional force (traction) between the tires & road surface III. Newton’s Third Law When one object exerts a force on a second object the second one exerts a force on the first that is equal in strength & opposite in direction Bill Nye & Newton's 3rd Law A. Action & Reaction - When a force is applied in nature a reaction force occurs at the same time -Even though the forces are equal, they are not balanced because they act on different objects EXAMPLE: A swimmer “acts” on the water, the “reaction” of the water pushes the swimmer forward Action and Reaction a net force, or unbalanced force, acts on the swimmer so a change in their motion occurs B. Momentum --momentum-- a product of mass & velocity - Momentum symbol p - Unit for momentum kg · m/s 1.) Force & Changing Momentum -By combining acceleration equation & force equation Newton’s 2nd Law Equation: ***Final Momentum mvf ***Initial Momentum mvi C. Law of Conservation of Momentum -Momentum of an object doesn’t change…. …UNLESS …its mass, velocity, or both change! Newton's Cradle -Momentum can be transferred from one object to another! Law of Conservation of Momentum: If a group of objects exerts forces only on each other their total momentum doesn’t change 1.) When Objects Collide - Results of a collision depend on the momentum of each object - When an object hits another from behind momentum occurs in the SAME direction - When an object hits another head on with the same force momentum is ZERO - If one object hits another head on with the more/less force momentum is TRANSFERRED