# lab 3 - NEWTONS SECOND LAW Purpose To verify Newton's laws...

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NEWTON’S SECOND LAW Purpose: To verify Newton's laws when applied to an aircar that is allowed to slide down a frictionless inclined plane. Apparatus: Air track, Motion Sensors and Computer, Air blower, Glider, Wood blocks, Card attachment for glider, Balance, Force sensor, Mass, micrometer and string(Make sure aircars are clean on the underside!! Also clean the airtracks when air is blowing.) Background: We would like to verify Newton's second law Σ F = m a E q . 1 ) and determine if the law is valid. Because the law is so general no one experiment can prove the law conclusively. We will apply Newton's laws to a situation and then verify the theoretical results by experimentation. Let us examine the situation of a block of mass M sliding down a frictionless inclined plane. From practical experience we know that the block will slide down the plane. By applying Newton's second law we can determine the rate of acceleration. Θ Figure 1. Illustration of the two forces, the normal force N, and the weight mg, that cause the block to slide down the inclined plane. From figure 1, Mg, the weight of the block, and N, the normal force, are the only two forces acting on the block. Applying Newton's second law yields Σ F = N +m g = m a E q . 2 ) This is broken down into x and y components 10

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Σ F x = mgSin( Θ ) = ma Eq.3) Σ F y = N - mgCos( Θ ) = 0 E q . 4 ) The object cannot accelerate in the y direction so the forces along that direction must be in equilibrium and equation 4 results. Along the x axis the forces are not in equilibrium and the block accelerates down the plane. From equation 3 the net acceleration of the block is equal to a = gSin( Θ ) = constant. Eq. 5) Here we see that the acceleration is strictly due to gravity and the angle of the incline. In this situation the mass of the object does not affect the acceleration of the block. This fact is not true in all situations. For forces not due to gravity, like a force from a spring, we should not forget the role that the mass of the object plays. In this experiment we will try to verify that equation 5 describes the acceleration of a block sliding
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lab 3 - NEWTONS SECOND LAW Purpose To verify Newton's laws...

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