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Topic 1.docx

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SCI 206
Andrew Morton

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Topic 1 Thursday, October 05, 2006 1:56 PM Topic 1: Motion From Lecture Newton's Laws  What are the 3 ways to describe motion? o Position, velocity, and acceleration  How can we describe position? o We use a vector, because it can tell us direction and distance (from some defined start point)  What are the 2 parts of velocity? o How fast we are going (speed) o What direction we are going in (direction)  What is acceleration? o It is how fast (and in what manner) our velocity is changing  What is Newton's first law? o An object that is not subject to any net outside forces moves at constant velocity  What is Newton's second law? o The force exerted on an object is equal to the product of the object's mass times its acceleration o The acceleration is in the same direction as the force  What is Newton's third law? o For every force that one object exerts on a second object, there is an equal but oppositely directed force that the second object exerts on the first object Gravity and Componential Motion  What is gravity? What determines the effect we will experience due to gravity? o It is a downward force produced by the earth which acts on us, pulling us down o The gravitational effect we experience is always an acceleration of ~10 m/s2 -- REGARDLESS of our mass  This means that (neglecting air resistance) a feather falls just as fast as a brick  Why doesn't gravity cause us to fall through the floor? o Because of the "normal force": an upward force produced by the surface we are standing on that counteracts the gravitational force so that we don't move  Describe the motion of a projectile launched at some angle with respect to the horizontal. o We can break up its initial velocity into horizontal and velocity components  Its horizontal velocity will never change, because there are no forces present to change it (recall Newton's First Law)  Its vertical velocity will be subject to gravity, so its upward progress will slow, eventually become zero, then start to head downwards  If you wanted to shoot a monkey in a tree, where should you aim? (Assume that the monkey will drop and fall downwards as soon as the shot is fired). o You should aim straight at the monkey (not above it or below it), because once the bullet is in the air and the monkey has dropped, both objects are subject to the same force (only gravity), and so they will meet at some point Work and Energy  What is the difference between kinetic and potential energy? o Kinetic energy is the energy of movement: the amount of this one possesses is related to one's velocity o Potential energy is stored: the amount of this one possesses is related to its ability to unleash energy  Discuss energy conversions. o Energy cannot be created or destroyed, but it can be converted from one form into another o The types of conversions which occur and their efficiencies affect the things we see in the real world  For example, some materials bounce better than others because they do a better job of converting kinetic energy to elastic potential (while others just convert kinetic into heat)  Discuss work, in particular the way it is related to potential energy. o To do work on something is to exert a force on it and cause it to move some distance in the direction of that force o Work is related to potential energy because we can give an object potential energy by doing work on it  For example, lifting a ball from the ground to a table Friction  Imagine a scenario where (with friction present) you are pushing a block horizontally across the floor. Describe the different forces acting on the box. o There is gravity acting downwards, and the normal force acting upwards o There is the human pushing force acting in the box's forward direction, and friction acting opposite to that  The pushing force must exc
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