Preliminary Considerations
We identified a force as an interaction between two objects. This interaction affected the motion of the object, but the overall effect of the interaction depends upon all of the force interactions (sum of the forces equals mass times accleration). The then a reasonable question is "what is being exchanged during the interaction?"
An analogy may help. When two people are talking, there is an interaction. The effect of the interaction is a change in the knowledge and understanding of the people. This interaction can be measured by the words which are exchanged. The transfer of these words is called a conversing.
Forces affect motion. So, it would seem reasonable to quantify the exchange of the force with some measure of its success. Motion is measured by velocity. But, to ultimately give it meaning in a coordinate system, the time duration for the velocity is needed to relate it to the change in position (displacement) in the coordinate system. Since the magnitude of the force measures the stength of the interaction and displacement measures the effect, a reasonable measure of what is exchanged is the force along the direction of displacement times the displacement. The process of this exchange is called "WORK". In equation form:
Work = F along displacement (+ if in the same direction as d, - if opposite) d displacement of object
In the cases shown below is the work positive, negative or zero?
In the first case, the force
and displacement are in the same direction, so, the work is
positive.
In the second case, the force and displacement are in the opposite
directions, so, the work is negative.
In the third case, the force and displacement are perpendicular and
not in the same direction at all, so, the work is zero.
In the forth case, the displacement is zero, so, the work is
zero.
The quantity that is exchanged is called "ENERGY". In other words, work is the exchange of energy between objects via forces. If the net force, Fnet = ma, and the constant acceration equations are used, the equation for the net work can be derived:
.
The term on the right is identified as kinetic energy, 
,
a measure of motion.
Just as there are many forms of
communication (e.g., gestures, writing, drawing, speaking), there are
many forms of energy. These form include kinetic energy of motion
(),
potential energy of gravity near the earth (
),
potential energy of a spring (
),
thermal energy, light energy, sound energy, chemical energy, and
nuclear energy.
These forms of energy became identified gradually by applying the princple of Energy Conservation. This principle states that the total amount of energy is constant. It may be transformed into different forms and exchanged between objects, but the total is constant. In various equation forms:
Every time this principle has failed to work, we have found a form of energy previously unknown (e. g., nuclear energy before the last couple hundred years) or some energy form which was left out of the equation (e.g., didn't include all the thermal energy generated by friction). Two other terms often associated with energy are work and heat. They are verbs which represent the transfer of energy, work is energy transfered by forces and heat is thermal energy transfer.
Note there is an important aspect of energy conservation: to do the same thing requires the same amount of energy, regardless of how quickly the transfer takes. How quickly the transfer occurs is called power. If there is more power, it means the task is done faster but with the same energy. (It is like the relationship between velocity and displacement, the displacement depends not only on the velocity but also how long it takes.) We confuse energy and power beacue of physical limitations of the delivery system. For example, a person can't run as long as a person can walk. That is a physical limitation to our body. Once those limitations are accounted for, then it becomes obvious power and energy are related but different.
Apparatus
string, two mass holders, various masses, smart pulley, ULI interface, computer
Suggested Procedure
Hang different masses on either side of the smart pulley via a string (this set up is called an atwood's machine).
Hold the masses at different heights. Call the lower height zero and measure how high above it the upper mass is (in actuality, you can call zero anywhere you want, often the ground is defined as zero).
Start recording position and velocity for the smart probe and let go of the masses. (Note the velocity is the same amount for each mass, but the sign is different, one is going down which is often negative and the other is going up which is positive. The postion readings will need to be converted to obtain the height for each mass.
Consider differnt masses.
Consider starting with a non-zero velocity.
Analysis
Taking the height, mass, and velocity data, test energy conservation for the two mass system (E mass 1 + E mass 2 = E total) by calculating the total energy before the masses are released and comparing the energy at various points after the mass is released. Assume there is only kinetic energy for the masses and potential energy from gravity for the masses. How should the total energy compare at any momment in time for the motion?
Follow up Questions
Based on your data, can you determine if all the forms of energy were accounted for (explain)?
What is work?
How can you determine when work occurs / is present?
What is heat?
How can you determine when heat occurs / is present?
What is energy?
Give some examples of energy.
You double the mass of an object, has its energy changed (explain)?
You double the temperature of an object, has its energy changed (explain)?
You double the height of an object, has its energy changed (explain)?
You change the speed of an object, has its energy changed (explain)?