Newton’s Second Law

Newton’s 2 nd Law When a coin is flipped in an airplane moving at constant velocity, where will the coin land?  In the persons lap  Newton’s 1 st Law  A body in motion will stay in motion.

Newton’s 2 nd Law If the coin is flipped as the plane accelerates during take off, where will it land? Behind the person. Newton’s 2 nd Law The coin is in constant motion while the plane accelerates

Newton’s 2 nd 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 2 nd 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. The Newton is a unit of FORCE. (One Newton is about the same weight as a ¼ lb. hamburger.

Newton’s 2 nd 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 2 nd 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 2 nd Law If the thrust were lessened, what would happen to the plane’s speed?  Decelerate  The air resistance > the thrust

Newton’s 2 nd Law Acceleration is directly proportional to net force  a ~ Fnet As the net force increases, how does acceleration change?  Acceleration increases

Newton’s 2 nd Law Acceleration is defined as the rate of change of velocity.

Newton’s 2 nd Law Acceleration is produced by a net FORCE being applied to an amount of matter. Write the equation for Net Force: F net = ma

Newton’s 2 nd Law  This is Newton’s 2 nd Law of Motion.

Newton’s 2 nd 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 2 nd 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 2 nd 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 2 nd 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 2 nd Law Newton’s 2 nd 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 2 nd Law We can use Newton’s 2 nd 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”. F wt = mg (same formula as F = ma) The unit for force is the Newton. What is the Newton equivalent to using fundamental units? kg*m/s 2 (hint: Simply plug in the units for mass and acceleration.)