Introduction to Machines
Part One
This website was created by a Kirkwood High School student as part of an Honors Physics program. It is designed to educate you about simple machines and the physics concepts that they operate on. The following pages are designed to introduce you to this website.
It's all about energy:
What is energy? Energy is something that enables you to do work. When you walk or run you are expending the chemical energy that your body stores. That energy comes from whatever foods you eat in the form of carbohydrates, proteins and fat. The energy in the lunch meat you ate came from an animal who ate other animals or plants. The energy from plants comes from the nuclear fusion reaction in our sun. Thus, in an indirect manner, the sun's energy is what powers the human body. Energy takes many different forms. These forms are:
- Light energy - Light, such as from a flashlight (includes all forms of EM radiation, visible or not)
- Heat energy - Such as from a fire
- Chemical Energy - Gas in a car has energy contained in it
- Sound Energy - Anytime you hear something you are hearing energy
Energy can be converted from one form to the other, but it can NEVER be created or destroyed. Never. No machine is capable of producing it's own energy- a machine must get it from another source. In the case of simple machines the energy required comes from the person moving the machine. Energy is commonly measured in a unit called Joules. A Joule is a simple name for Kilograms x Meters Per Second Squared x Meters. This is quite a mouthful so the name "Joule" was given to it and it is now commonly represented as an uppercase "J." There are two distinct types of energy:
Potential Energy: Potential energy is any type of stored energy. Examples of stored energy are a coiled spring and a battery (that is not dead). Theoretically this energy could be stored forever. In physics we say an object has potential energy when it is elevated off of the ground or other frame of reference. In this circumstance you can calculate the Potential Energy (P.E.) of any object that is elevated above the ground using this equation:
The above equation represents the potential energy for any object that is above the ground.
Equation Analysis:
- P.E: The total potential energy an object has based on it's position. This energy is expressed in Joules.
- m: The mass of the object, in kilograms.
- g: The acceleration due to gravity, in meters per second squared. On Earth this number will always be 9.80665, but you can use 10 if you want.
- h: How high the object is off the ground, or other reference point. This number is expressed in meters.
Kinetic Energy: Any object that is moving has kinetic energy. Any object. While your car is speeding down the interstate at 70 miles per hour your car (and you) have kinetic energy. A very formidable example of kinetic energy in action is the bullet from a gun. However if you took that same bullet and threw it through the air with your hand you would probably not hurt anything. As you might have guessed kinetic energy is based on speed. Like potential energy it is also based on mass as a two ton truck literally bowls over a compact car. This is the equation for kinetic energy:
The above equation represents the kinetic energy for any object, moving or immobile.
Equation Analysis:
- K.E: The total kinetic energy an object has in Joules.
- .5: Multiply by one-half. Always.
- m: The mass of the object in kilograms.
- v2: Velocity squared. This means that if the velocity doubles the amount of kinetic energy quadruples.
Energy, Distance and Power:
Energy and distance have a very important relationship. In fact, the amount of energy you must expend to move an object is directly related to how much the object weighs and how far you must move it. But there is a very, very important thing that you must understand first: Work is only done when you move an object vertically! This means that if you move an object horizontally only then the amount of work you do to it is ZERO. The following equation will calculate work for lifting an object against the pull of gravity. In most cases this will be the normal force of the object, which is mass times gravity.
The above equation represents the amount of work you do to an object.
Equation Analysis:
- W: The work you do to an object, in Joules of course.
- F: The force that you work against. In some cases you must also add the frictional force.
- d: The vertical distance you moved the object.
Power is an important concept that you should learn before we go on to the next section. It describes how fast work can be done. This is essential to understanding how good a machine is, as the more power it has the faster it can do work. Physical power is measured in a unit called watts, just like on the light bulb. The watt was named after James Watt, the man who is credited with inventing the steam engine. Now let me show you an equation to calculate just how powerful something really is:
This equation represents how much power something (such as a machine or a person) has or shows in a certain experiment.
Equation Analysis:
- power: How powerful something is. Power is measured in watts.
- work: How much work something does in an object, in Joules.
- time: How long it took to move the object, in seconds.
You have now learned some of the basic concepts of energy. If you would like, you could go on to part 2, or read this section again to make sure you have everything. In the future should you need to refer back to this section simply click the introduction tab above.
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