1. Do now
Quick write [1 min]: Write down every single thing you know or have heard about energy

2. Unit 3: Energy and Momentum Conservation
Energy Objectives:
1. Define work and calculate the work done by a force.
2. Calculate the kinetic energy of a moving object.
3. Determine the gravitational potential energy of a system.
4. Calculate the power of a system.
5. Apply conservation of energy to analyze energy transitions and transformations in a system.
6. Analyze the relationship between work done on or by a system, and the energy gained or lost by that system.
7. Use Hooke's Law to determine the elastic force on an object.
Calculate a system's elastic potential energy.

3. Conservation Principles
The most powerful concepts in science are called "conservation principles". These principles allow us to solve problems without worrying too much about the details of a process.
We just have to take a snapshot of a system initially and finally; by comparing those two snapshots we can learn a lot.

4. Conservation Principles
A good example is getting change for a dollar bill.
If you know that you have a dollar bill before the transaction, it doesn’t matter what the person giving you change gives you as long as it is worth one dollar. He/She can give you 4 quarters, 20 nickels, 10 dimes, 100 pennies or any combination and it will be fine as long as it is still worth one dollar.

5. Conservation of Energy
Energy is a conserved property of nature. It is not created or destroyed. Therefore in a closed system we will always have the same amount of energy.
The only way the energy of a system can change is if it is open to the outside...this means that energy has been added or taken away [or if someone gives/takes away money].

6. Conservation of Energy
If we call the amount of energy that we start with "Eo" and the
amount we end up with as "Ef" then we would say that if no energy is added to or taken away from a system that
Eo = Ef
It turns out there are only two ways to change the energy of a system. One is with heat (which we won't deal with here) the other is with Work, "W".
If we define positive work as that work which increases the energy of a system our equation becomes:
Eo + W = Ef

7. Work
Work can only be done to a system by an external force; a force from something that is not a part of the system.
So if our system is a plane on an aircraft carrier and we come along and push the plane, we can increase the energy of the plane…
We are essentially doing work on the plane.

8. To summarize, Work can be defined as:
The amount of work done, and therefore the amount of energy increase that the system will experience is given by the equation:
W = Fdparallel
Meaning, work is the product of the force applied which moves the object a parallel displacement
To summarize, Work can be defined as:

9. Question
If you are pushing really hard on a wall and you break a sweat, are you doing any work on the wall?

10. The energy of the system is unchanged; a state of equilibrium.
Work
If the object that is experiencing the force does not move (if dparallel = 0) then no work is done.
The energy of the system is unchanged; a state of equilibrium.

11. Positive Work
If the object moves in the same direction as the direction of the force (for instance if force and displacement are in the same direction) then the work is positive: W > 0.
The energy of the system is increased. F M
Distance
Acceleration occurs due to the unbalanced force.
Work is the ability to cause change.

12. Negative Work
If the object moves in the direction opposite the direction of the force (for instance if force and displacement are in opposite directions) then the work is negative: W < 0.
The energy of the system is reduced. F
Distance M
Acceleration occurs due to the unbalanced force.
Work is the ability to cause change.

13. The energy of the system is unchanged.
Zero Work
If the object moves in the direction perpendicular the direction of the force (for instance if force and displacement are at right angles) then the work is zero: W = 0.
The energy of the system is unchanged.
FNormal
Distance M
No acceleration occurs due to the fact that no component of force acts in the direction of displacement.
In this case, no work is done by the normal force and/or the force of gravity.

14. Units of Work and Energy
W = Fdparallel
W = F*d
= [N][m]
= [kg* m/s2][m]
= [kg * m2/s2]
= [J]
In honor of James Joule, who made critical contributions in developing the idea of energy, the unit of both work and energy is also known as a Joule (J).
James Joule

15. NOTE:
Even though we are talking about the direction of the force and distance being parallel, energy and work are still scalar values! You can’t have 100J North or 5J to the left.

16. Practice Problems
TOQ worksheet [All types of problems that can be asked about this topic]

25. Finish this worksheet – Presentations tomorrow!
Classwork/Homework
Finish this worksheet – Presentations tomorrow!