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Download Newton’s Second Law of Motion Force & Acceleration
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Newton’s Second Law of Motion Force & Acceleration Introduction to Science A. King EHS Acceleration • Galileo define rate of change of velocity as acceleration. • The term acceleration is typically used when the velocity increases. • The term deceleration is typically used when the velocity decreases – another way of saying this is that “deceleration” is when negative acceleration is occurring. • In both cases, “acceleration” is the process that’s actually occurring. Calculating Acceleration ΔV Acceleration = --------t Where ΔV is the change in velocity and t is the time it takes for the velocity to change. ΔV : : acc xt Units for Acceleration • Speed and velocity are easily measured in distance/time units, such as miles/hr, m/s, etc. • Units of acceleration are more complicated, and have to take other stuff into account. • Sample problem: What is the acceleration if we speed up from 10 km/h to 30 km/h in 10 seconds? • Acceleration = Δv/t • (30 km/h – 10 km/h)/ 10 sec = • 2 km/h/s Acceleration depends on the net force. Acceleration ~ net force. Mass • Mass is a measure of an object’s inertia and a measure of how much material an object contains. (It depends on the number and kind of atoms making the object up.) • Mass is measured in grams: grams, kilograms, milligrams… Weight • Weight depends on gravity. • Weight is the force due to gravity that acts on an object’s mass. • Although weight and mass are different from each other, they are directly proportional to each other. • 1 kilogram weighs 9.8 newtons. Volume • Volume is a measure of space. Newton’s Second Law states: • The acceleration produced by a net force on an object – is directly to the net force. – Is in the same direction as the net force. – Is inversely proportional to the mass of the object. – In formula: F = m x a By using consistent units, such as newtons (N) for force, kilograms (kg) for mass, and meters per second squared (m/s2) for acceleration, we get the exact equation: Δv v f – vi Acceleration = -------- = ---------t t Acceleration Problems • While drag racing out of our school parking lot, I time myself at a speed of 40 meters per second seven seconds after starting. What was my acceleration during this time? • A = vf – vi / t • = (40 m/s – 0 m/s )/7s • = (40 m/s)/7s • = 5.7 m/s/s Friction • Occurs when one object rubs against something else. • Occurs for solids, liquids and gases. • Always acts in a direction opposite to motion. • The amount of friction between two surfaces depends on the kinds of material and how much they are pressed together. Free Fall • When an object is dropped in a place with gravity (k.e. not deepspace), gravity causes the object to fall downward. • When this occurs, the object is said to be in “free fall.” • For problems like this, we’ll imagine that gravity is the only force that’s acting on the object – wind resistance and other stuff will be ignored. How fast is an object moving in free fall? • The increase in speed per second is the • Let’s consider the acceleration which in following data table: this case is 10 m/s/s. Elapsed time Instantaneous (sec) speed (m/sec) • The instantaneous speed of an object that is 0 0 accelerating is equal to 1 10 the acceleration 2 20 multiplied by the amount of time the object is 3 30 falling. t 10t • In equation form: v = at Δv Formulas : : acc x : : acc x t F vf - vi Wt d v t : : : : : : : : mx a mx g ½ g x t2 a xt