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Newton’s Second Law Continued

Newton’s Second Law Continued. You learned that when you are calculating force and have to take gravity into account you must add 9.8 m/s 2 to the acceleration What must you do when you are calculating Acceleration?

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Newton’s Second Law Continued

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  1. Newton’s Second Law Continued

  2. You learned that when you are calculating force and have to take gravity into account you must add 9.8 m/s2 to the acceleration • What must you do when you are calculating Acceleration? • You must multiply 9.8 m/s2 to the mass and then subtract it from the original force!! • Why? • This will convert your mass into a force and allow you to adjust your force for the effect of gravity • Remember:1 kg = 9.8 kg x m/s2 or 9.8N • If you have an object that has a mass of 50 kg how many N is that: 9.8 m/s2 x 50 kg = 490 kg x m/s2 or 490 N

  3. Example • You apply a force of 50 N to lift a package with a mass of 4 kg. Calculate the resulting rate of acceleration of the package.

  4. Solution • F = M x A or A = F/M What do we know? F= 50 N M = 4 kg We can’t just plug gravity into the formula!!!! Remember the gravitational constant is an acceleration rate!!!! However 1N = 9.8 kg x m/s2 So by multiplying your mass times the gravitational constant you now can deal with gravity 4kg x 9.8 m/s2 = 39.2 kg x m/s2 or39.2 N A = (50N – 39.2N)/4kg A = 2.7 m/s2

  5. Newton’s Second Law Continued • Question? • If you throw object from a certain height and also drop an object from the same height which one will hit the ground first? • Neither – they both hit at the same time!!

  6. Projectile and Circular Motion • What is a projectile? • Anything that is thrown or shot through the air • Horizontal Motion • Once you throw a ball no other force accelerates it forward (ignoring a tail wind and air resistance) so its horizontal velocity is constant. • Vertical Motion • When the object thrown starts being pulled downward, horizontal motion has turned into vertical motion • Now the ball has constant horizontal motion (due to inertia) however it has increasing vertical velocity

  7. So what is the answer to the question? • Penny demonstration. • They will both hit at the same time. Gravity still exerts the same acceleration rate

  8. Question? • How does a roller coaster work?

  9. What about curves? • If you are moving at a constant speed in a straight line there is no acceleration!!! • However, if you enter a curve, even if you have not changed speed you have accelerated!!!

  10. Curves • The change in direction of the velocity is toward the center • The acceleration towards the center is known as centripetal acceleration

  11. Roller Coasters • In order for acceleration to occur when in a curve there must be some unbalanced force acting on the object. • Centripetal Force – the force acting toward a center of a curved or circular path • Examples: A car driving on the road. The centripetal force is the friction between the tires and the road • Roller coaster – the friction between the track and the wheels of the car

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