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Chapter 5 Momentum & Impulse Terms Predicting motion requires us to understand motion. Useful terms โข Acceleration โข Force โข Impulse Acceleration Acceleration is the rate at which an object changes speed. It is measured in units of speed per units of time ๐๐โ 60 miles per hour per 4 seconds, 60 4๐ Every four seconds, the speed increases by 60 mph 9.8 ๐ ๐ 9.8 meters per second per second, ๐ Every second, the speed increases by 9.8 m/s Acceleration Acceleration can be expressed symbolically โ๐ฃ ๐= โ๐ก Where ๐ = acceleration โ๐ฃ = change in velocity โ๐ก = change in time Forces Force is a push or a pull. When forces are unbalanced, they cause acceleration. Measured in Newtons or pounds 1 Newton ~ weight of 1 apple on Earth 1 pound ~ 4.5 N Acceleration & Force The amount of acceleration experienced by an object is proportional to the amount of force acting on it. bigger force ๏ฐ bigger acceleration The amount of acceleration is inversely proportional to the mass of the object. bigger mass๏ฐ smaller acceleration Acceleration & Force The relationship between acceleration, force, and mass can be represented symbolically: ๐น ๐= ๐ Where ๐ = acceleration ๐น = net force on object ๐ = mass of object Not-so-secret universe ๐= โ๐ฃ and โ๐ก ๐= Therefore โ๐ฃ ๐น = โ๐ก ๐ and ๐โ๐ฃ = ๐นโ๐ก ๐น ๐ And soโฆ ๐โ๐ฃ = ๐นโ๐ก To change an objectโs speed or direction requires force to be exerted on that object. โข Quick changes in speed require lots of force โข Long changes in speed require less force. Think about transportation safety devices. How do these devices take advantage of this principle? When the change in your velocity is from something large to zero (e.g., if you are in a car crash), you want the force acting on you to be small. Airbags extend the time. When you are trying to karate chop a wood block in half (i.e., when you change the velocity from zero to something), you want the force to be large. A quick, abrupt motion shortens the time. Impulse Impulse, often abbreviated ๐ผ, is a measure of the length of time, โ๐ก, that a force, ๐น, is applied. ๐ผ = ๐นโ๐ก Reported in units of Newton ๏ท seconds. How much? How much?