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Newton’s Second Law Newton’s 2nd Law When a coin is flipped in an airplane moving at constant velocity, where will the coin land? In the persons lap Newton’s 1st Law A body in motion will stay in motion. Newton’s 2nd Law If the coin is flipped as the plane accelerates during take off, where will it land? Behind the person. Newton’s 2nd Law The coin is in constant motion while the plane accelerates Newton’s 2nd Law If the coin is flipped as the plane decelerates while landing, where will it land? When the plane decelerates as the coin is flipped, the coin will stay in constant motion as the plane slows down. Newton’s 2nd Law When acceleration is equal to zero, the net force is also ZERO. Whenever something isn’t accelerating, all of the forces balance out to zero. FORCE. (One Newton is about the same weight as a ¼ lb. hamburger. The Newton is a unit of Newton’s 2nd Law If 18 tons of thrust are required for an airplane to move at a constant velocity ( zero acceleration ), how much friction force is there? 18 tons constant velocity = 0 acceleration Newton’s 2nd Law If more thrust were used, what would happen to the plane’s speed? Increase in speed (acceleration) Find a higher constant velocity Newton’s 2nd Law If the thrust were lessened, what would happen to the plane’s speed? Decelerate The air resistance > the thrust Newton’s 2nd Law Acceleration is directly proportional to net force a ~ Fnet As the net force increases, how does acceleration change? Acceleration increases Newton’s 2nd Law Acceleration is defined as the rate of change of velocity. Newton’s 2nd Law Acceleration is produced by a net FORCE being applied to an amount of matter. Write the equation for Net Force: Fnet = ma Newton’s 2nd Law This is Newton’s 2nd Law of Motion. Newton’s 2nd Law It was Galileo who dropped objects and showed that they fall together with the same acceleration (if air resistance doesn’t count.) However, he could never answer why! Isaac Newton did! Newton’s 2nd Law The relationship between mass and acceleration is an inverse one. A ~ 1/m Inversely proportional As mass increases, acceleration decreases The relationship between force and acceleration is a direct one A ~ F net Directly Proportional As Force increases, acceleration increases Newton’s 2nd Law In the parachute example, are both parachutes accelerating? YES You know that there is a NET force acting on them both! As the parachute begins to fall, air resistance increases because they are accelerating. The greater the speed, the greater the air drag (resistance). Newton’s 2nd Law When air drag (resistance) equals the weight, the force on a falling person wearing a parachute is ZERO Newtons. Consequently, the acceleration is zero since there is no net FORCE. The velocity is CONSTANT; this is called TERMINAL velocity. Newton’s 2nd Law Newton’s 2nd Law is known as the Law of Acceleration: The effect of an applied force is to cause the body to move in the direction of the force. Net FORCE produces acceleration! Force tends to accelerate things, mass tends to resist acceleration. Newton’s 2nd Law We can use Newton’s 2nd Law to change mass to weight. Since all objects accelerate towards earth because of gravity, we replace “a” for acceleration in the equation wit “g”. Fwt = mg (same formula as F = ma) The unit for force is the Newton. What is the Newton equivalent to using fundamental units? kg*m/s2 (hint: Simply plug in the units for mass and acceleration.)