Newton and The Rollin Runs
A long time ago in England, a man named Isaac Newton did a bunch of physics. He probably also watched people and around him and thngs around him and what they did. He watched how Babbage shook when the trolley jerked, how the cabbage rolled out the Miss Polley's loot, and how the garbage dumped. He watched his weights and his sizes and he put too many twos side-by-side and sometimes added one more for good measure and he decided he had the right(!!!!) to make three Laws for mother physics. But he went first and sat under an apple tree and one fell... may be on his head.
First Law
A particle remains at rest or continues to move in a straight line with constant velocity if there is no unbalanced force on it.
There are certain parts to this statement that need some recognition. The word 'particle' means that the object has a very small size when considering what produces the actions such that you can ignore rotations or internal conditions.
'remains at rest' means that the particle sits and moves at the same speed and acceleration as what the observer sits on. For example if you were on a train and it was moving very fast at a consistence speed, the glass on your table will look to bee at rest.
'continues to move in a straight line with constant velocity' means that the particle moves without changing the speed from the point it was observed and it doesn't change direct also.
'no unbalanced force' means that any force on it has an opposing force of equal magnitude such that it appears there were no forces on it. Here is an example of one object acted upon by a four forces where two forces are balanced out completely.
The whole statement means that in the universe, any object doesn't change its speed or stays at rest or motionless unless something causes to change this condition by pushing or pulling or creating a field of some kind that produces an unbalanced force on it
What this means is that if you see anything moving at all anywhere, it is either moving with a constant or uniform speed or an unbalanced force acts on it. you could look for one: gravity, a dumb kid, an engine, a wind, a vibration? A field, for time being, is a stressed region in which particles experience forces due to those stresses
Second Law
The acceleration or change-in-velocity of a particle is proportional to the resultant force acting on it and is in the direction of this force
Now the force can cause the change but so what? Well, the truth is whether the object changes from one velocity to another or whether from rest it has to 'accelerate'. This means to 'change velocity'. This change can also be negative, and this means that the object slows down Also the acceleration acts in the same direction as the force that produces it. Look at the image:
You can see that the resultant force C produces an acceleration c that is in the same direction. But what about if the thing moves in a circle with a uniform velocity? Well, motion in a circle means an acceleration directed towards the center, which means there is a force towards the center of motion.
Third Law
The forces of action and reaction between interacting bodies are equal in magnitude, opposite in direction, and collinear
This means that when you apply a force on an object, it applies the same amount of force to you, in the exactly opposite direction. Now you may wonder why an object moves when you push on it. Its because the point at which you are pushing gives back the same force, but it shares this force inward in such a way that it offers less of a resistance to your push in that direction. Look at the diagram below:
Inside the material, the reaction force is distributed and outside, it is distributed into many parts of which only a small portion may push at you. In empty sspace, you will have no resistance coming from outside so the object moves.
Force And Acceleration
There is a relationship between force and acceleration according to the second law:
F = ma
F -> force
m -> mass of object
a -> acceleration experienced
Believe or not, this mass, m, is a constant of proportionality here. Lets work one example.
A man uses his finger and impiges it on a box of 400kg and finds out he moves it from 0m/s
to 1.05m/s in 3 secs. Find the force he applies to the box in that time.
solution
let a represent acceleration
a = (v2-v1)/change-in-time
where v2 and v1 are final and initial velocities
therefore a =(1.05-0)/3 = 0.35
F = ma = 400(0.35) = 140 newton
Momentum: Can You Stop It?
A 'quantity of motion' is a product of the mass of an object and its velocity. What am I saying. You will recall that the formula for acceleration is:
a = (v2-v1)/change-in-time
so..
F = ma
F = m((v2-v1))/change-in-time
F = mv2-mv1)/change-in-time
let G1 = mv1
and G2 = mv2
ΔG = G2-G1
so F = ΔG/change-in-time
G1 -> the momentum when speed was v1
G2 -> the momentum when speed was v2
No comments:
Post a Comment