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Transcript
Chapter 4 Newton’s First Law of Motion: Inertia Newton’s First Law Inertia In Fancy Terms: Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it. In Plain English: Objects in motion tend to stay in motion. Objects at rest tend to stay at rest. Inertia Definition: the reluctance of any body to change its state of motion Examples of Inertia Alphabet soup Removing tablecloth with dishes still on the table http://www.youtube.com/watch?v=QbGV6qQcJrw http://www.youtube.com/watch?v=aCqQzrPCcFM&feature=related So Why Do Things in Motion Stop? Forces Definition: any push or pull Friction Definition: the force that acts between materials that touch as they move past each other - caused by irregularities in the surfaces of objects that are touching - Even very smooth surfaces have microscopic irregularities that obstruct motion MASS a measure of inertia measured in kilograms MASS AND WEIGHT ARE NOT THE SAME THING!!! Mass: quantity of matter in an object - independent of location Weight: force of gravity on an object - depends on an object’s location Mass and Weight are Proportional but NOT Equal a lot of mass = a lot of weight SI unit of mass – kilogram SI unit of force Newton 1 kg = 9.8 Newtons (N) weight = mass x gravity w = mg http://www.youtube.com/watch?v=aCqQzrPCcFM Net Force Definition: combination of all forces acting on an object The net forces changes an object’s state of motion In the absence of a net force, objects do not change their state of motion Normal Force Definition: the upward force that balances the weight of an object Also called support force Other forces: Tension: At equilibrium – Tension = weight Equilibrium Net force = zero Chapter 5 Newton’s nd 2 Law Remember: Acceleration = change in velocity time interval What causes acceleration? Force An objects acceleration is directly proportional to the net force Acceleration ~ net force Mass resists acceleration Acceleration ~ 1/mass (inversely proportional) Newton’s nd 2 Law: The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object. In other words: Acceleration = net force/mass a= F/m Net Force Unit will always be Newtons. 1 N = 2 kg*m/s Free Body Diagram Definition: Diagram showing all the forces acting on an object. Applying Force Pressure = force per unit of area Measured in pascals (Pa) 2 Pascal = N/m Pressure = Force area of application P = F/A Pressure is increased when surface area decreases! ex. bed of nails Falling and Air Resistance Terminal velocity: speed at which acceleration of a falling object is zero because friction balances weight Free Fall Explained F = m F m Chapter 6 Newton’s For rd 3 Law every action there is an equal and opposite reaction All actions occur in pairs Action: Object A exerts force on Object B Reaction: Object B exerts force on Object A Newton’s Law of Universal Gravitation Every object is attracts every other object with a force that for any two objects is directly proportional to the mass of each object. In other words, the greater the masses, the greater the force of attraction between them F = G m1m2 d where G = 6.67 x 10-11 Nm2/kg2