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Chapter 8: Energy

Chapter 8 Intro of Energy **-** Energy is the most central concept underlying all of science. Concept of energy is relatively new, it is engraved, not only in the branches of science, but in nearly EVERY ASPECT OF HUMAN SOCIETY. We find energy in the form of sunlight, it is in the food we consume, and it helps is in sustaining life. Although energy is common in all science and used in all science, it is the most difficult to define.  = 8.1 = = = = 8.2 = = =
 * __Work__ -** Work is done by lifting mass against gravity, the heavier the mass, more work and energy input is required. There are two situations in which work can be done, the **application of a force**, the **m****ovement of something by a force.** Work is measured in Joules (J), a combination of a unit of force (N) and a unit of distance (m).
 * Application of a force** can be expressed mathematically by **work = force x distance** or **W=Fd**. For an example, when you lift a load up one story, you do less work than you would if you were carrying twice the amount. An example of non-work is lifting weights. When you bench press, and hold the weight above yourself. This may seem to be considered work, but do not let Work fool you! You are not actually "doing work".This is not work at all, because there is no movement or force taking place after one repitition. Work can be done on the muscles by stretching and squeezing them, but work is not done on the barbell.
 * Movement of something by a force** is when you simply use a force to move an object. For example, when a bowler bowls a ball down the lane, he applies a force on the ball, and depending on the force, that's how much work is put in over a distance. You do work on an object when you force it to move against the influence of an opposing force, which is often friction.
 * Example problem: Lets say that Haris pushes a cat with a force of 8 newtons. The cat moves a distance of 20 meters, how much work is being done on the cat?
 * Answer: W=FD so (8N)(20m)=160J
 * __Power__ //-//** Power is similar to work except it deals with time. It is just the amount of work done over a specific time interval. The mathematical expression is power = work done/time interval, with the mathematical unit being the watt (W) (Joule per second). For example, two engines can produce work. However, just because one produces more work, doesn't mean that it can go faster than the other engine.
 * Example problem: Mr. Strong exerts 130 J of work on his door. It takes the door a total time of 10 seconds to open. How much power is Mr. Strong doing?
 * Answer: Because power=work done/time... P=(130J)/(10s)=13W



= 8.3 = Mechanical Energy- The energy due to the position of something, or the movement of something. There are a total of two types of Mechanical Energy, and those are potential energy and kinetic energy.

= 8.4 =   Gravitational potential energy= weight x height or PE=//mgh//** PE=//mgh//**
 * __Potential Energy__ - **The energy that is stored and held in readiness (PE). An example of potential energy is a compressed or stretched . Another example is when pulling an arrow back with the string of the bow. At the moment there is no energy in the bow, but there potential energy for when you let go of the end of the arrow and the string, the arrow will fly. Potential energy is not always visible to our eye either. Did you know that it is in foods, fossil fuels, electric batteries, and chemicals? Well it is! Lets say that you have a ramp, and at the top of the ramp, is a ball. To elevate objects, such as this ramp, requires work because you are working against earth's gravity. The potential energy of elevated objects is called gravitational potential energy. The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity in lifting it. Work done equals the force required to move it upward times the vertical distance it is moved. Upward force required whiling moving at constant speed is equal to the weight, //mg//, of the object, so the work done in lifting it through a height //h// is the product //mgh.//**

=  = = 8.5 =  __Kinetic Energy-__ Energy of motion, equal to half the mass multiplied by the speed squared. **Kinetic Energy= 1/2 mass*speed^2 or KE= 1/2mv^2**
 * Example Problem: Haris tosses a microwave in the air a total distance of 2 meters. The microwave weighs approximately 20 kilograms. What be the microwaves potential energy?
 * Answer: (20kg)(10m/s)(2m)=400 J
 * Example Problem: Moe weighs exactly 60 kg. If young, defenseless Moe were to be pushed down a steep mountain at about 33 m/s, what is the total kinetic energy he would create?
 * 1/2(60kg)(33 m)^2= 32670 J.

= 8.6 =  __Conservation of Energy (Law of Conservation of Energy)__  - Energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes. The equation is mghi+ 1/2mv^2i = mghf + 1/2mv^2f**. m=mass. g=gravity. h=height. v=velocity.

** = 8.7 = __Machines:__ **a device used to multiply forces or simply change the direction of forces. A good example is a lever. At the same time you do work on one end of the lever, the other end does work on the load.**
 * Work input = work output
 * And because work equals force times distance -> (force * distance)input = (force * distance)output.

__Mechanical Advantage__ **- the ratio of output force to input force for a machine.**
 * Neglecting friction, mechanical advantage can be determined by the ratio of input distance to output distance. MA = din/dout.

= 8.8 = __Efficiency__ **- the ratio of useful work output to total work input.
 * Efficiency = useful work output / total work input or Wout/Win
 * Efficiency can also be expressed as actual mechanical advantage/theoretical mechanical advantage or MA/TMA.

= 8.9 = Energy to Life - Every living cell in every organism is a machine. Just like any that can operate, cells need energy to work. Similar to how there is more energy stored in gasoline than in the products of its combustion, there is more energy stored in the molecules in food than there is in the reaction products after the food is digested. The energy difference is what sustains life.