Unit 04 -- Work & Energy

Vocabulary

1. Work -- the product of the force and the distance moved because of the force. If the force and the object's displacement are not in the exactly same direction, only the component of the force that is applied in that direction can be used to determine its amount. It is required to change the energy in an object. It is symbolized with a capital W and is measured in units of Joules, where one Joule is equal to one Newton * meter. It is a scalar quantity.
2. Power -- the time rate of work done. It is found by dividing the amount of work or energy consumed in a process by the time it takes to apply that work or energy to the process. It is symbolized with a capital P and is measured in Watts, where one Watt is equal to one Joule per second.
3. Energy -- the property of an object or system that allows it to do work. It is symbolized with a capital E and all forms of it are measured in Joules, just like work. Regardless of what form it takes, it is a scalar quantity.
4. Mechanical Energy -- the energy commonly used by machines to do work. It is the energy an object has due to its position (potential energy) or due to its motion (kinetic energy.) It can be found by adding the total potential energy stored in an object to its kinetic energy.
5. Potential Energy -- the energy an object possesses because of its position. This is true only if there is a force that attempts to restore the object to its original rest position, as a spring does when you stretch it out or as gravity does when you lift an object up above the floor. It is equivalent to the work that must have been done to move the object away from its rest position. It is symbolized with a capital U and is measured in Joules.
6. Kinetic Energy -- the energy an object possesses because of its motion. It is similar to momentum in that it depends on both the mass and the velocity of the object, but, unlike momentum, the velocity is much more important for this quantity. It is symbolized with a capital K and is measured in Joules.
7. Work - Energy Theorem -- it states "the amount of work done on an object equals the amount of change in the kinetic energy of that object." Though this specifically describes changes in kinetic energy, work can also transfer other forms of energy as well.
8. Law of Conservation of Energy -- it states "energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy in a closed system does not change."
9. Machine -- a device that can increase or decrease the amount of force applied to it or simply changes the direction of the force. Since its use is subject to friction, the amount of work or energy that is put in is always more than the work or energy that can be gotten out of it.
10. Lever -- one of the simple machines. It consists of a rigid bar that is allowed to pivot at one point (called the fulcrum.)
11. Mechanical Advantage -- the amount a force is multiplied through the use of a machine. It is found using the ratio of the force you get out of a machine to the amount of force that you put into it. As a ratio, it has no units.
12. Conservation of Energy -- the amount of work or energy gotten out of a process cannot exceed the amount put into that process. If the process is ideal, the work or energy gotten out of a process is equivalent to the work or energy put in.
13. Efficiency -- the percentage of the work or energy put into a machine that is converted into useful work or stored energy. Another way to think of it is the ratio of useful work or energy to the total work work or energy put in. As a ratio, it has no units.

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