(2)+Newton's+Second+and+Third+Laws

PAGE EDITORS: Katya Landau, Elena Tepavac, Marissa Goldstein


 * Due 11/16/09**


 * CHAPTER 2: NEWTON'S SECOND LAW**

- when an external force acts on an object of mass "m", the object will accelerate directly proportional to the net force. - **Force** : a vector quantity
 * Fnet = ma** or **net force = mass x acceleration applied**
 * Fnet = ma** or **net force = mass x acceleration applied**
 * direction of the force, that is physically applies, matter
 * unit : **kilogram(meters/ seconds squared) = Newton "N"**

Factors that affect friction : -mass -texture -force of gravity (Fg = mg) -force applied -surface area -moving or not?


 * Ffr o< Fnormal** or force of friction = inversely proportional to the normal force

Coefficient of friction (miu) - constant determined experimentally by surfaces in contact
 * coefficient of kinetic friction (miu k)
 * coefficient of static ffriction (miu s)

--> --> EF = ma** or **sigma = mass x acceleration**
 * E = sigma

--> --> cause** = **effect**
 * Fnet** = **ma

--> --> cause = effect**
 * a = __Fnet__**
 * m

NEWTON'S THIRD LAW
-If object 1 exerts a force on object 2, object 2 will exert a force equal in magnitude but opposite in direction back onto object 2. - Action- Reaction Pair Pairs of the equal and opposite forces involved in Newton's Third Law - Must be the same kind of force ( i.e. applied force and the applied force back onto object 1 by object 2) - Force must be applied onto two objects Example: When you lean against a wall, you exert a force on the wall. The wall simulatneously exerts an equal and opposite force on you, hence you do not topple over. Force/ Mass= Acceleration When a cannonball is fired the force applied to the cannon ball (which results int he cannon ball being catapulted into the air) is matched by the force the cannonball exerts back onto the cannon. If these forces, due to Newton's third law, are equal, then why do we see such an obvious change in the motion of the ball compared to the cannon? This is because the cannon is more massive than the ball, so when the force is exerted from the cannon to the ball and from the ball back onto the cannon, even thought they are equal forces, the effect of the force is more noticable in the cannonball due to its lesser mass. The same applies when you kick a football. In most cases the ball will go flying when you seem to have no effect. Even though the force you apply to the football is equal to that the football exerts back onto you, the football goes flying to its much lower mass than that of yourself. Who is touching who? In this situation it is apparant that the girl is touching the boy, but technically the boy is touching the girl also because of Newton's third law. Example: The way rockets propell into space is somewhat due to Newton's third law. The rocket expells exhaust in an "explosion" type way which in turn applies that force back onto the rocket, propelling it upward.



