To work or not to work
In the SI system, the unit for work is in Joules. 1 Joule could also be written as the following (is equal to):
What is 1 Joule = 1 N · m
An object can have potential energy by virtue of its surroundings. Name two examples of potential energy and where it would exist.
Answers could include two of the following: a wound-up spring, a stretched elastic band, or an object at some height above the ground.
Like matter in chemistry, energy cannot be created or destroyed, instead, "un-used" energy goes through this process and gets:
What is Transformed?
Power is the rate at which this is done.
What is work? Power is the rate at which work is done.
This category of forces does not give regard to storing up and saving mechanical energy.
What are non-conservative forces?
Centripetal forces do not do work because of this reason.
Centripetal forces do no work, as they are always perpendicular to the direction of motion.
The force required to compress or stretch a spring is commonly written as: Fs=-kx. What does k represent and will it's value always be the same?
What is k is called the spring constant, and needs to be measured for each spring?
If there is a nonconservative force such as friction, the kinetic and potential energies go, or rather get transformed into this:
What is heat?
True or false: Power is needed for acceleration and for moving against the force of gravity.
If this type of force is present, the work done depends not only on the starting and ending points but also on the path taken. List the category of force and give an example.
What are non-conservative forces and friction?
Other examples accepted: air resistance, viscous forces, etc.
Ezra can run up the stairs in 13 seconds. Ryan can run up the same stairs in 15 seconds. Who did more work?
Both Ryan and Ezra did the same amount of work. This is because work is not a time-based quantity, as seen in its equation, W=Force·Dispalcement.
When looking at the potential energy in relation to a spring, does the force increase as the spring is stretched or compressed further?
What is yes, the force does increase.
We have primarily studied mechanical energies in class, but recently reviewed some other forms of energy; name 3 of those other forms.
What is Electric energy, nuclear energy, thermal energy, and/or chemical energy.
This person was a British scientist who invented the steam engine. He discovered the power of his engine compared to that of a horse by measuring how fast an average horse could do work and invented the unit "Horsepower" from it. What is his name?
Who is James Watt?
The following equation is used to calculate work within what kind of force category:
W=∆KE+∆PE
Work done by nonconservative forces is equal to the total change in kinetic and potential energies.
It is a known fact that work cannot be done on an object that remains at rest, due to this reason:
Work requires that a force acts over a distance. If an object does not move at all, there is no displacement, and therefore no work done.
The equation for gravitational potential energy is defined as PEG=mgy. When considering this kind of potential energy, when would the potential energy become kinetic energy?
What is potential energy can become kinetic energy if the object is dropped?
Accounting for all forms of energy, we find that the total energy does not do this or this (2 different words).
What is increase or decrease?
Micah performed 5 J of work in 10 secs. Sophia did 3 J of work in 5 secs. Who produced the greater power?
Sophia did more work. Since power = work/time, we see that Micah produced 0.5 W and Sophia produced 0.6 W of power. Thus, even though Micah did more work, he required twice the time to do the work, and therefore his power output was lower.
Potential energy can only be defined or derived for this category of forces:
What are conservative forces?
Mia pushes twice as hard against a stationary brick wall as Anna. If you compare the amount of work each of them did, who did more work?
What is both do zero work. Neither Mia or Anna did any work on the wall due to it being stationary and not moving any distance.
Potential energy can only be dervived in regards to this category of forces:
What is conservative forces? Other acceptable answers would be to list conservative forces such as gravitational, electric, or elastic.
True or false: If a stone is dropped with an initial gravitational potential energy of 100 J but reaches the ground with a kinetic energy of only 75 J, this is a violation of the principle of conservation of energy.
What is false? The rest of the energy was transformed on the fall down into thermal energy.
In your lab last Tuesday you looked at a variety of variables that affect power and work; how did changing the mass (you vs. your partner) influence the work and power output while climbing the stairs?
What is an increase in power? More work is done when mass increases. Therefore the power increases as well.
If there are no nonconservative forces, the sum of the changes in the kinetic energy and in the potential energy is equal to this:
What is zero?
The kinetic and potential energy changes are equal but opposite in sign. This allows us to define the total mechanical energy: E = KE + PE.