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Lecture 5

# ISCI 2000 Lecture 5: REVIEW

5 pages71 viewsFall 2017

Department
Interdisciplinary Science
Course Code
ISCI 2000
Professor
Pam Wolff
Lecture
5

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TOPIC I: Motion:
1. Understand how humans can tap into the force of gravity to get useful energy.
Relate energy to power in the context of human generation and use of electrical
power.
2. Know what factors affect the theoretical maximum energy available from a
conventional hydroelectric dam, and calculate this maximum energy from the
specifications of the dam and the water source. Understand where useful energy
is lost in the process.
3. Recognize the factors that affect the trade-off between the human and
environmental impacts of a dam and the desire to maximize the energy output.
Motion. Motion is converting movement into usable forms of
energy. Examples of these could be tidal power or hydroelectric
dams
So, hydroelectric generation. The kinetic energy that water has as it falls can
be converted to other forms of energy such as electric energy. When looking
at the height of a dam, you want to look at how high the reservoir of water
is, which is called the head height. You always want to build a dam higher
than the reservoir of water, because it calculates for if the reservoir were to
grow. If the dam was not high enough then it could lead to overflow and
flooding. This can cause many problems including population resettlement,
changes in the wildlife habitat and the height dictates the energy.
Also when looking into a dam you have to account for gravity. Gravity acts
upon a downward force on water pressure. Pressure is generated as the
water goes down the generator and eventually in the water wheel. When
positioning the water wheel, you don’t want it too far up nor do you want it
to be too low, because it can get clogged with sand and silk. And then is
flow of a dam. Flow is the mass of water that goes by in a given amount of
time (m/t)
And with flow comes power. Power is the amount of energy (in joules)
generated in a given time interval (usually in 1 second intervals). You will
get your power in a Joule (J) per second which is equal to a Watt (W). But
for a dam, water is continuously moving, so power = flow rate x g x h (in J/s
= a Watt)
4. Relate displacement, initial velocity, final velocity, acceleration, and time. Be able
to solve for any one if three are known (and understand that this means that they
are all interdependent!)
Motion is converting movement into usable forms of energy.
Motion can be described in: distance (in meters delta x), the displacement (in
meters delta x), acceleration (which is usually due to gravity, example water
falls and is measured in meters squared and because its due to gravity
[downward]: its ALWAYS 10m/s^2) and velocity (in meters per second)
which you want to look at in two steps. Initial velocity (which is looking at
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things when there is no time gone by) and final velocity (after the time has
passed). The last variable of the 5 is time (which is looked at usually in
seconds).
All you need to know is that as long as you know 3 out of the 5 terms, the other
2 can be determined (mostly because the universe has determined it).
THIS MEANS THAT THEY ARE ALL INDEPENDENT!
5. Relate Gravitational Potential Energy (GPE) to the acceleration due to gravity,
height and mass.
gravitational potential energy (or G.P.E or just P.E for short) is energy due to its
position above the ground. This is equal to mass times the acceleration due to
gravity times the height above the surface.
6. Relate GPE to Kinetic Energy (KE) once an object falls.
The form of energy that the object is at the top (before it falls) is potential
energy. As the object falls it goes into the energy of motion. It “spends” its
potential energy in exchange to gain velocity. Potential energy is converted to
Kinetic energy (K.E). Kinetic energy is the energy due to movement. So
kinetic energy is equal to half of the mass times the velocity squared. This is
important, because the potential energy at the top is equal to the kinetic energy
at the bottom and vice versa. This is a good thing to know because sometimes
it’s easier to calculate the potential energy at the top, rather than the kinetic
energy at the bottom. If you calculate one, you have the other. Another thing to
note is that energy is calculated in Joules.
7. Understand the law of conservation of energy, and where useful energy can be
lost.
As the law of conservation states, that all of the energy of a system is conserved
none is lost or gained, meaning it is often converted from one form or another, so
we have to try to keep track of it. For example, looking at a ball falling freely
what is equal is the change in potential energy that equals the change in kinetic
energy, because you’re dealing with conservatory forces and therefore, the total
energy is conserved. So, since the total energy is constant, if the potential energy
goes down, then the kinetic energy goes up. But, useful energy can be lost when
you can’t create any more energy inside the system, for example when you’re
boiling a kettle, some of that energy can be converted to sound and/or heat to
their surroundings and therefore that is wasted energy
8. Compare dams with other gravity-based systems such as wind power, tidal power,
and run-of-river generation.
Run- ofriver generation: this is when we use the mass of moving water using
the current. It is a small-scale generation of a water wheel.
Tidal power: also uses the mass of moving water. It can generate a lot of energy
but it needs a tide to do so which can be a downside. Therefore it needs to be
strategically placed otherwise it won’t generate enough energy. It can disrupt
shorelines and wildlife but not as much as dams. Tidal power is good in natural
waterfalls because it affects the ecosystem less there.
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