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Newton’s 2 nd Law

Learn about Newton's 2nd Law and its applications in physics, including constant speed and acceleration. Explore concepts such as statics vs dynamics, pressure, and the law of falling bodies.

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Newton’s 2 nd Law

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  1. Newton’s 2nd Law Or Accelerating Your Dynamic Range

  2. Newton’s 2nd Law • a~Fnet (direct proportion) • a~1/m (inverse proportion) • a=Fnet/m • a and Fnet in same direction • Vector equation

  3. No net force on object SFx=0 SFy=0 SFz=0 Motion is that of constant speed Examples include car cruising at constant speed, airplane moving forward at constant speed, masses held stationary by ropes, falling bodies after reaching t.v. Net force on object SFx=max SFy=may SFz=maz Motion is that of constant acceleration Examples include car speeding up, slowing down or changing direction, airplane diving or climbing or changing speed, falling bodies before reaching t.v. Statics vs. Dynamics

  4. Pressure • Pressure = force / area • Dance skit • Bed of nails demonstration • More nails better than less nails • Less force better • More area better

  5. Law of Falling Bodies Explained • Kindergarten Skit • Inertia greater for larger mass • Net force greater on larger mass • F/M = f/m = accel of gravity • True if NO air resistance or if object has not reached terminal velocity

  6. Falling w/ Air Resistance Air resistance • Terminal Velocity (T.V) • Fastest speed object falls at weight • Weight = air resistance => mechanical equilibrium • Varies directly w/ mass and inversely w/ area • Prior to terminal velocity • W constant, A.R. increasing, F net decreasing • A decreasing, v increasing, d fallen each second increasing • After terminal velocity is reached • W=AR, F net=0 • A=0, v= t.v., d fallen each second constant

  7. Different Masses in Freefall Hits t.v. b Hits t.v. b a b • Which has the higher t.v.? • Which reaches t.v. first? • Which accelerates longer? • Which hits ground with higher speed? • Which hits ground first? a

  8. Check Question 1 • What is the acceleration of a 10 kg block of ice that has a net force of 50 N placed on it? • 1) 500 m/s/s • 2) 5 m/s/s • 3) 1/5 m/s/s • 4) 0 m/s/s

  9. Check Question 2 • The road pushes the tires of a car with a force of 5000 N. Air resistance pushes in the opposite direction with a force of 1000 N. If the car has a mass of 2000 kg, what is the acceleration of the car? • 1) 2 m/s/s 2) 2.5 m/s/s • 3) 5 m/s/s 4) 1/2 m/s/s

  10. Check Question 3 A styrofoam and golf ball are dropped from rest at the same height. Answer the following • Which has the greater TV? • Which accelerates longer? • Which has the greater velocity when it hits the ground? • Which hits the ground first?

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