Newton's Laws of Motion

Newton's First Law of Motion:
This law talks about INERTIA.  It means that an object that is at rest wants to stay at rest unless a force acts upon the object.  This means that an object will continue to stay still unless something makes it move.  Also, an object in motion wants to stay in motion unless a force changes its motion.  That means that if an object is moving there must be a force such as friction or air resistance to cause that object to stop.  An object already moving must also have a force act upon it in order to change its direction.  If something is traveling straight, it must hit a wall, another object, a bump in the road, or encounter another change in force to make it change its course of motion.

Newton's Second Law of Motion:
This is the law that tells us that F=m*a or Force = Mass times Acceleration.  This means that the force an object has can change depending on the mass of the object and the acceleration of the object.  We experienced this the day we did the three different labs.  One team rolled a car down a ramp into the back of another car and found that the faster the car traveled the further the second car moved.  Another team swung a pendulum into a cardboard object.  When the mass of the pendulum was increased, the distance the cardboard was pushed increased.  The third team used the force plate to determine the amount of force a ball had when dropped from different heights.  The higher the ball started, the more acceleration it had when it hit the force plate and therefore it had more force.

Newton's Third Law of Motion:
This law is the law that says every action has an equal and opposite reaction.  We've talked about this with the Normal Force.  Remember the example of a book sitting on a table?  The normal force is a force that the table pushes onto the book and it is equal and opposite of the force of gravity.  The other example we discussed in class is an astronaut firing a gun in outer space.  The astronaut would fly backwards with the same amount of force as the bullet being propelled from the gun because when a gun is fired, the bullet and the person experience a force that is equal and opposite.  Force diagrams are great ways to show these forces because the vectors indicate the direction of the force and the length of the vector arrow tells us how strong the force is.  When the arrows face opposite directions and are the same length, that shows us on the force diagram that the forces are equal and opposite.