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Newton’s Second Law of Motion Force and Acceleration Chapter 12-2 I. Galileo Developed the Concept of Acceleration A. Galileo developed the concepts of speed, velocity, and acceleration B. Used experiments with inclined planes and noticed the speed of balls changed as they rolled C. What does Δ mean? D. 3 Types of Acceleration 1. When something GAINS speed it is ____________________ 2. When something slows down it is decelerating or _____________ acceleration 3. Acceleration occurs when an object _____________ ______________ E. Acceleration 1. In 1s we steadily increase velocity from 30km/h to 35km/h. In the next second we increase from 35 km/h to 40km/h. What is our acceleration? F. Acceleration 1. Acceleration is a measure of the change per second of _____________ 2. (meters per second) per second 3. So when the units are m/s2 the 2 means that there are 2 units of time, NOT that the number is squared Write example here: 4. Free Fall is when5. A freely falling object gains speed at the rate of 10 m/s each second 6. When an object is thrown up it is moving against gravity it’s speed changes at ___________________ II. Force Causes Acceleration A. ________________ is caused by applying a force B. Net Force- combination of all forces that act on an object C. Acceleration is directly proportional to the net force: if net force is ____________ acceleration is ______________ D. Direction of acceleration is in direction of net force III. Mass is a Measure of Inertia A. If the same force is applied to an empty can and a can filled with rocks, which will accelerate more? B. Mass is an indication of an object’s inertia AND a measure of how much material an object contains C. ______________ is a measure of space in units such as cubic centimeters, cubic meters, and liters E. Weight is a measure of the pull of _______________ F. Mass and Weight are ___________ proportional G. SI unit for mass is kilogram (kg) H. SI unit for force is Newton (N) I. 1 kg object has a weight of 9.8 N and is generally rounded to 10 N J. Mass Resists Acceleration 1. More massive objects are ______ ____________ to accelerate 2. Acceleration is ______________ proportional to the mass 3. More mass means less acceleration IV. Newton’s Second Law Links Force, Acceleration, and Mass A. Newton’s Second Law states: The acceleration produced by a net force on an object is 1. directly proportional to the _______ ________ 2. in the ___________ direction as the net force 3. inversely proportional to the ________ of the object B. Acceleration= net force/mass 1. 2. What is the acceleration of a 1000 kg car pulled by a force of 2000 N? V. Friction is a Force that Affects Motion A. Friction occurs when an object rubs against something else 1. This is true for all states of matter What are the states of matter? B. ALWAYS acts in a direction to oppose motion C. Air drag is D. The surfaces can reduce or increase friction What surface can increase friction? What surface can reduce friction? E. Inclined surfaces reduce friction F. No change in motion occurs when ΣF = 0 VI. Objects in Free Fall have Equal Acceleration A. Free Fall acts on falling objects 1. 2. All other forces, like air drag, are neglected B. Acceleration of Free Fall __________ ___________ depend on mass VII. 2nd Law Explains Why Objects in Free Fall Have Equal Acceleration A. Newton’s 2nd Law says we must consider not only weight, but also mass when considering free fall B. All freely falling objects have the same ratio of force to mass and undergo the same acceleration at the same location Draw the force/mass ratio for small weight and big weight: C. Acceleration due to gravity is g and is 10m/s2 VIII. Equal Acceleration in Free Fall A. Weight of a 1 kg stone at the earth’s surface is 10 N. What is acceleration of the stone? B. Weight of a 10 kg boulder is 100 N. What is this acceleration? C. A 5kg bag of sand has a weight of 50 N. When dropped its acceleration is a=50N/5kg=_____m/s2 IX. Acceleration of Fall is Less When Air Drag Acts A. Air drag depends on _________ and ____________ ____________ B. Increased air drag results in reduced acceleration C. When air is present the downward net force = _______________________ D. As an object falls faster and air drag increases, acceleration gets less and less. E. When the net force of the air drag equals the weight then net force is __________ F. Terminal speed is when acceleration no longer occurs. Terminal velocity is when we look at speed and direction.