Newton's Second Law

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The acceleration of an object is directly proportional to the net force acting upon it. The constant of proportionality is the mass.

Fnet=MA  A=Fnet/M

Force = A push or pull that one object exerts on another object. M = Mass. A= Acceleration. A car is moving at 6 m/s. Let’s assume that the wheels of a 5-kg car apply 10 N of net force. What is the acceleration if friction and drag are negligible? Net Force = MA 10 = 5A Acceleration = 2 m/s2 A car is moving at 6 m/s. What is the net force if the wheels of the 5-kg car apply 10 Newtons but a 1-kg parachute applies 3 Newtons in the other direction?   The net force would equal 3 Newtons. The total mass = 6 kg. What is the acceleration of the car? Acceleration = Fnet/M Acceleration = 3/6 Acceleration = 0.5 m/s2 A car is moving at 6 m/s. A rocket is added to the car and applies an additional force of 10 Newtons. The wheels still apply 10 N. What is the net force if the parachute continues to apply 7 Newtons in the other direction? The total mass of the car, rocket and parachute is 10 kg.   The net force would equal 13 Newtons. The total mass = 10 kg. What is the acceleration of the car? Acceleration = Fnet/M Acceleration =13/10 Acceleration =1.3 m/s2

 Big masses are hard to accelerate. It is hard to speed up or slow down big masses. Big masses require big forces to change speed. It is hard to change the direction of motion of a big mass. Small masses are easy to accelerate. Small masses require small forces to change speed. It is relatively easy to speed them up and/or slow them down. It is easy to change their direction of motion. Objects move in the direction they are pushed or pulled. Objects accelerate more quickly when a greater force is used.

Assume that both steam engines below apply the same amount of force.

 A heavy train has a difficult time accelerating. Big masses require big forces to change speed. Acceleration = Force / Mass Acceleration = 100% / 100% Acceleration = 1 When the same force is applied to a less massive train its acceleration is greater. Small masses require small forces to change speed. Acceleration = Force / Mass Acceleration = 100% / 10% of the big train Acceleration = 10 times greater than the big train

Law 1: Inertia

Law 3: Action/Reaction

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