Thursday, November 22, 2012

Newton's Second and Third Laws


Here is a summary of the notes I took on Newton's 2nd and 3rd Laws.

Newton’s 2nd Law
·      A=f/m
·      Relationship that shows force is prop. to acceleration and mass is inversely prop. to acceleration
·      Inversely proportional: if mass increased by 2, acceleration would DECREASE by 2
·      Proportional: if force is increased two times greater, acceleration also increases 2 times more

Examples of 2nd Law
·      A ball hitting a wall and bouncing back
·      A hammer striking a nail into a piece of wood and the hammer ”bounces” back

·      This picture shows how acceleration and mass are inversely proportional, but force and acceleration are proportional


Newton’s 3rd Law
·      The force from the 1st object to the 2nd object is ALWAYS equal to the force from the 2nd object to the 1st object
·      Even if only one object is pulling, force is still equal
·      Dealing with two objects, not just one
·      Forces are separate for each object

Examples of 3rd Law
·      A person standing on a skateboard, pushes on a wall, and accelerates backwards.
                              
o   The wall is applying a force to you causing you to move backwards
o   The person accelerates because only one force is acting on the person
o   The force of the person pushing the was and the table pushing back are independent of one another

·      This picture shows how a rocket is launched into space using Newton’s 3rd Law

Review Questions to Remember

·      When skydiving, at what point is the net force…
o   0N?
§  When diving at a constant speed; terminal velocity
o   -_N?
§  When free falling; before reaching terminal velocity
o   +_N?
§  When the parachute has deployed

·      When skydiving, why is acceleration positive when parachute is deployed?
o   To slow down, accel. must be in opposite direction of velocity, and velocity is negative when skydiving, so accel. is positive

·      If an astronaut is traveling alone in space and needs to get back in the shuttle, how can he do this?
o   Push off of (or throw) tools he has with him in opposite direction of where he needs to go

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