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## CHAPTER 3

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**Newton’s Second Law of Motion**• F = m x a • Force = mass x acceleration • The faster you run into a wall, the more force you exert on that wall • Units are kg m/s^2 • Units are Newtons (N)**F = m x a**• You run into the wall at 50 N of force. Your mass is 10 kilograms. Calculate your acceleration. • Carmine has a mass of 100 g, and he is running toward you at 2 m/s^2. Calculate the force he will hit you with. (Tricky)**Friction**• Friction is the force that opposes motion between two surfaces touching each other • There are 3 types: • 1. static = not moving • 2. sliding = pushing a heavy box across the floor • 3. rolling = your car spinning its wheels on the ice**Air Resistance**• Air resistance affects anything moving in earth’s atmosphere • The amount depends on the speed, size, and shape of the object • Negating air resistance, which will fall faster: a feather or a bowling ball?**Terminal Velocity**• The force of air resistance increases with speed • Remember that the acceleration due to gravity is always 9.8 m/s^2 • When the object is falling so fast that it cancels the force due to gravity, it is now at terminal velocity and is no longer accelerating • This is the greatest falling velocity possible**Law of Gravitation**• Any two masses exert a gravitational force on each other • The size of this force depends on the mass and the distance between the objects • Greater the mass, greater the force • Closer together, greater the force**Weight vs. Mass**• Weight = mass x acceleration due to gravity (9.8 m/s^2) • Weight is in Newtons • Weight is a force • Mass is in kg • Mass is the measure of amount of matter an object contains**Calculating weight**• How much does a person with a mass of 70kg weigh on planet Earth? • How much does a baby with a mass of 500g weigh on planet Earth? (Tricky)**Projectile Motion**• When you throw a ball on Earth, there are two forces working on it • Vertical force pulling down (gravity) • Horizontal force pushing out (your throw)**Newton’s Third Law of Motion**• For every action there is an equal and opposite reaction • Ex: rocket propulsion**Momentum**• momentum = mass x velocity • p = m x v • Law of Conservation of Momentum • Momentum can be transferred from one object to another • Total momentum of the system remains the same**Calculating momentum**• Compare the momentums of a 50kg dolphin swimming 16.4m/s and a 6,300kg elephant walking 0.11m/s.