2007-10-12
Today's nonsense
- Brook and the coffee stain on the ceiling due to "coffee vapor"
- "Eachother" and "a lot" v. alot
PV = nRT = Boyle's law
- Homework
Lots of notes and information today on Sir Isaac Newton and some of his contributions to the wonderful world of physics. We're on chapter 4 now. Isaac Newton is also responsible for the calculus stuff. He's the guy that causes headaches every now and then. Newton presented three fundamental laws of physics.
Newton's first law the law of inertia. An object at rest, stays at rest, unless acted on by an external force. As well, an object in motion continues in motion at constant velocity unless acted on by an external force.
Force-- an external influence on an object that causes it to accelerate relative to an inertial reference frame. Do you see how this can be never ending?
Reference frames-- a set of coordinate systems at rest relative to each other Should "each other" be one word?
Inertail reference frame-- a reference frame in which the law of inertia holds exactly. So suppose you saw you were outside, and a dog went past you at 60 mph? That dog's velocity is zero if its frame of reference is the car that it's riding in. As the car slow down, the dog's velocity remains zero.
Mass - an intrinsic property of an object that measures it's resistance to acceleration. If it's moving, it's going to continue moving. So if you take two objects and give them the same force, and one takes off faster, what can you tell me about the mass of the two objects? The one that accelerates less has the more mass. So, it's a measure of the object's inertia. So how easy is it to change it's inertia? You can't change mass, that's an intrinsic property, it's the same no matter where you are. Weight is different of course.
The ratio of two masses is defined quantitatively by applying the same force to each and comparing their accelerations. How would you measure the mass of something on the moon? Well, you would have a standard mass, and then you'd have to apply equal forces to each one, and find the accelerations which is the change in velocity over the change in time.
m2 / m1 = a1 / a2
The mass of the standard object (so, if you have a standard object, its mass is 1 kilogram) is 1 kg. The force required to produce an acceleration of 1 m/s^2 on the standard object is defined to be 1 newton (N).
Newton's Second Law
The acceleration of an object is in the direction of the net external force acting on it. You can have forces from different directions, but we add up all of those force-vectors, and the resultant force is your net force. So this is all of the i's and the j's and vector components and vector manipulation and so on. It is proportional to the net external force and is inversely proportional to the mass of the object:
VectorA = VectorForce / (mass of the object on which the force is applied)
OR: VectorF = mass * VectorAcceleration
Then: the sum of the forces is equal to the net force.
Physics homework due Tuesday.
-- Read about the dog that can travel at 60 mph