Showing posts with label physics. Show all posts
Showing posts with label physics. Show all posts

Friday, June 9, 2017

Differentiation

A Derivative of a function is the instantaneous rate of change of that function at a point. It's the limit as the change in x approaches zero of the average slope of a graph. The operation of taking a derivative of a function can be written in different notation, like f"(x) or d(f(x))/dx . The rules for taking derivatives of some basic functions are outlined below:

if n is a constant and u and v v are functions of x
                                                 
when f(x)=                                             |                                                    f '(x)=
un                                                           |                                             u'(x)ᐧ (n)un-1 
nu                                                           |                                             u'(x)ᐧln(n)nu
n                                                             |                                                 0
uᐧv                                                          |                                          (u'(x)ᐧv)+(v'(x)·u)
u                                                             |                                        (u'(x)ᐧv)-(v'(x)·u)
v                                                             |                                                   v
u(v(x))                                                    |                                          u'(v(x))ᐧv'(x) (d(u(v(x)))/(v(x)) )(v'(x))
sin(x)                                                      |                                                   cos(x)
cos(x)                                                      |                                                   -sin(x)
tan(x)                                                     |                                                   (sec(x))2
cot(x)                                                     |                                                    -(csc(x))2
arcsin(x)                                                 |                                                 u'(x)ᐧ    1    
                                                               |                                                        √1-u2
arccos(x)                                                 |                                                     -u'(x)ᐧ    1    
                                                               |                                                               √1-u2
arctan(x)                                                 |                                                     u'(x)ᐧ    1    

                                                               |                                                               1+u2
ln(x)                                                       |                                                       1/x
log base a (x)                                         |                                                     1/x(ln(a))

to differentiate a function like xx,you need to use the natural log rule: ln(xu) =uln(x).
When given a table of values you can estimate the derivative at a point at or in between input values given.

If a function is differentiable on an interval then the function is continuous on the interval but if the  function is continuous on the interval then the function is not necessarily differntiable ( i.e. functions can be non-differentiable and continuous ( with sharp cusps and the like ).

The MVT states that if a function is continuous and differentiable on an interval [a,b] then the is some point c where f '(c) is equal to the slope between a and b or the average rate of change over the interval. Rolles theorem is a special case of the mean value theorem when the average rate of change is 0.


Do differentiate parametric functions you take the derivative of y with respect to t and then divide id by the derivative of x with respect to t.

To differentiate polar functions you use the definitions y=rsinθ and x=rcosθ and then use parametric differentiation.

Two take second derivatives ( f "(x) ) you take the derivative of the derivative, to take third derivatives you take the derivative of the derivative of the derivative or the derivative of the second derivative and so on.

To take derivatives of inverse functions at a point, you take the reciprocal of the derivative of the corresponding point.

When a derivative of a function is undefined or equals zero you have got a critical point of that function. You can use derivatives to determine if a function is increasing( i.e. the derivative is positive ), or decreasing ( negative f '(x) ), concave up or concave down ( the second derivative is positive for concave up and negative for concave down. ). These determinations can be used to find maxima or minima of functions. They can also be used to find where the concavity of the graph changes ( a inflection point). There are multiple methods to do this including finding critical points and evaluating the second derivative at the points ( second derivative test, if it is positive it is a local minimum , if it is negative it is a local maximum ), or evaluating f ' before and after the critical point.
Finding local maxima and minima and points of inflection are all part of derivative applications, like useful thing you can use differential Calculus for. Approximating the value of a function using slope tangent line approximation is also part of Derivative applications. Basically you use the equation
y-y1= f '(x1)(x-x1). Where you can approximate y values ( the y ) of x values ( the x ) near the  xvalue. The y1  is the y value at the x1.

Another application of derivatives is related rates. Which is when you have a object, and some measurement of it is changing at a given constant rate, while some other property or properties is/are changing at a non-constant rate. You use an equation that relates the two properties and then solve it for the rate of change of the non-constant one at some point in time.

One application of differential calculus has a bunch to do with Physics, namely the analyzation and study of the movement of a particle given its function of either , position, velocity, or acceleration with time. The derivative of position is velocity, the derivative of velocity is acceleration. Which means that the slope of a position versus time graph is the velocity and the slope of a velocity versus time graph is the acceleration. These definitions can help us analyze and determine when a particle is moving in a certain direction , when it is not moving, when it is slowing down or speeding up ( when the acceleration and velocity are in the same direction then the particle is speeding and when the velocity and acceleration are in different directions the particle  is slowing ), and how fast or how much a particle is accelerating at a point.

Differential calculus can also be used to solve optimization problems, in which you write a function for a thing to me maximized or minimized and then take the derivative(s) of that function to find the local an global maxima or minima.

Monday, May 15, 2017

AP Physics C:Mechanics

I took the AP Physics C:Mechanics exam last week, and it was a bit challenging, but I am pretty sure I passed ( for BYU that means get at least a 4 ). You see I had not studied it nearly as weel or as much or as enthusiastically as Calculus and I did not understand it as well and Calculus BC. The Physics exam had more than just math ( unlike the AP Calculus BC exam did ) it had theory and laws and you had to know how to solve the problems. Which luckily I did ( most of them ) but there were still some that had me a bit confused. The Free response especially , which had a whole question on the rolling motion of a ball , was confusing. But I believe that I wrote enough and got enough of the Multiple choice correct to get a 4.

The Exam is separated into two sections: multiple choice and free response , where the MC part has ~35 questions which you have to fill in a letter on a answer sheet, and the FR part has 3 questions where you have to write. You are given 45 minutes for both parts, and so an hour and a half for the whole exam. 

The Exam tests kinematics, forces and newtons laws, work and energy, linear momentum , impulse and center of mass, rotational motion, gravitation, and oscillations.

Kinematics deals mainly with the study of motion, how things move ( velocity, displacement, acceleration and the equations that relate these quantities and time ) and is only up to two-dimensional in AP Physics c mechanics with projectile motion. In this course both kinematics under constant acceleration and kinematics under varying acceleration are covered ,where in the first case the kinematic equations are used and in the second case calculus is used.

Forces and newtons laws deal with why objects move and the forces that make them move. The method of drawing free body diagrams and solving newtons second law equations (F=ma)  are covered as are the 3 laws ( inertia , F net = ma, action reaction pairs ). Inclined planes and force trigonometry is used to find components of forces in different directions. Different types of force, such as the normal force, the gravitational force, the frictional force and centripetal force are covered.

Linear Momentum is the mass of an object times its velocity or the integral of force with respect to time for varying forces. Impulse if equal to momentum as stated in the impulse-momentum theorem, and calculations are done on these equations. Conservation of linear momentum is covered and so are the different types of collisions ( elastic , inelastic and completely inelastic ). The method for calculating the center of mass of both a system of particles and a continuous body are also covered.

Work and energy deal with the integral of force with respect to distance ( for varying force), Mechanical , Potential , and Kinetic energy, potential energy graphs, conservation of mechanical energy, non conservative energy, basic gravitational and spring potential energy, work energy theorem , and power.

Rotational motion deals with the rotational analogous of the fore covered topics of kinematics and dynamics when rotating around a fixed axis ( so it can only rotate in two directions ), and how to solve problems with this. These include but are not limited to angular displacement , velocity, and acceleration, arc length , torque , rotational inertia, and rotational kinetic energy.

Gravitation deals with Kepler's 3 laws,Newtons law of gravity, actual gravitational acceleration, the equating of centripetal force and gravitational force for circular orbits, the finding of the gravitational force inside a sphere, the actual gravitational potential energy and the discovery of escape velocity, and the like

Oscillation deals with springs, the restoring force for simple harmonic motion, potential energy for springs, period and frequency, the model for sinusoidal simple harmonic motion of position, velocity and acceleration, pendulums and the simple harmonic motion equations for ones that are displaced a small angle of theta.

It is so awesome how newton discovered these laws that rule the motion of objects ! Our Heavenly Father loves it when we strive to find the truth and with his help we do. He helped me learn Physics and I am so thankful for this.



Saturday, February 15, 2014

United states of America VS Russia ( ice hockey )

U.S.A. Played Russia today in ice hockey for the Winter Olympics. It was an intense game. Who won this was practically going to win the group. Russia scored first. 0-1. P. Datsyuk scored it. Then C.Fowler scored for U.S.A.. They stayed tied for some time . There was a lot of tension. The Americans and Russians got called for Interference. They both had shots on net. But the keepers were good, They were: Jonathan Quick( U.S.A. ) and Sergei Bobrovsky ( RUS ). But U.S.A. got one past Sergei Bobrovsky with J. Pavelski.U.S.A. was happy . But then Russia got back with P. Datsyuk again. It was looking worse for U.S.A.Then Russia Scored again ! It bounced of the post and went in. But the Refs came and said NO GOAL! They said the net was not in place. So U.S.A. still had a chance. Russia was mad. They played a hard game. It was still 2-2 at the end of regular time. Then overtime came. U.S.A. had a one-on-one with the Sergei Bobrovsk but they could not score it. Overtime ended with a 2-2 tie. It was up for shootouts. U.S.A. started it off good with a goal by T.J. Oshie. Then E. Malkin(R) missed. J. van Riemsdyk(U) could not score. P. Datsyuk ( Scorer of Russias 2 goals ) missed. J. Pavelski (U)did not score. I. Kovalchuk scored for Russia barley saving them. T.J. Oshie missed and I. Kovalchuk missed. T.J. Oshie scored and P. Datsyuk scored. T.J. Oshie scored and I. Kovalchuk scored. T.J. Oshie missed and P. Datsyuk missed. Then T.J. Oshie scored and I. Kovalchuk missed !!! U.S.A. Won!! 

Wednesday, June 6, 2012

Ballista physics

I made a Lego Ballista with my dad from physics workshop
 we did an experiment to see which angle it shot the farthest from and we found out that at the angle 45°
as you can see  at the graph i made below. it started from 0° got higher and higher until it reached 45° then it got lower and lower and it ended at 90°. at the bottom you can see a P3 that means power three we were shooting at power three . at 80° it goes farther if you shoot it at P5  then at P3 56°.
 

Sunday, December 19, 2010

Genius Game

This week I had a birthday. I got a game that was called Genius.

It's a physics game where you build different inventions and sell them and solve problems.
I'm learning about steam engines, pulleys and how fast something goes. I also learned how to tell a real gold coin by its density. I also learned that you can't make energy out of nothing.

I had to build a waterworks and a water tower so the fire department would work and protect buildings from fire.

I built a bicycle factory which uses coal for energy. Later I made a building to make iron. With coal and iron I could make steel and build a train factory.

I also had to build houses for workers to live in. They like to live not too far away from the factories and not too close to them either. They also like to live by trees and to have their wages paid very good or they will go on strike. They are especially happy when I build a museum or schools.

I made $30,000 in the game but I spent a lot of it building new factories.

My dad helps me with the math, but it's a lot of fun.