1. C6 – Introduction to Energy
Get a spring
General Physics

2. Two Minute Problems – C6T.1
Which has the larger kinetic energy, a 50-kg person running at a speed of m/s or a 5-g nickel falling at a speed of 200 m/s?
A. The running person
B. The falling nickel
C. Both have the same kinetic energy
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3. Two Minute Problems – C6T.3
A person throws three identical rocks off a cliff of height h with exactly the same speed v0 each time (see the figure). Rock A is thrown almost vertically upward, rock B is thrown horizontally, and rock C is thrown almost vertically downward. Which rock hits the ground with the greatest speed? (Ignore friction)
A. Rock A B. Rock B
C. Rock C D. All rocks hit
E. Other with same speed
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4. Two Minute Problems – C6T.6
There is no way to experimentally determine the actual value of a system’s total energy, true (T) or false (F)?
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5. Energy in interactions between two particles
Total energy involved in an interaction between two particles is defined as
K1 is the kinetic energy of one particle
K2 is the kinetic energy of the other particle
V(r) is the potential energy that depends on the distance between the particles
E, K1, K2, and V(r) are all scalar quantities
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6. Total Energy General Physics
The gravitational interaction between two particles transforms gravitational potential energy to the particles’ kinetic energies without changing the system’s total energy.
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7. Energy of multiparticle system
The energy of a multiparticle system is the sum of the kinetic energies of the particles and potential energy of the interaction between the particles
The potential energy of the
interaction between particles 1 and 2
The kinetic energies of
particles 1, 2, and 3
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8. Energy conserved for ISOLATED system
Internal interactions between particles involves only transfers between kinetic and potential energies.
The system’s total energy is not changed by these INTERNAL interactions
External interactions can change the kinetic or potential energies of the particles in our system
Total energy is conserved only for ISOLATED systems
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9. Kinetic Energy Energy of a moving particle SI unit of energy
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10. Ignore earth’s kinetic energy
Ratio of kinetic energy of objects
If m1 is something of normal mass, and m2 is the earth, this implies that
When something of normal mass interacts with the earth, the earth’s kinetic energy can be completely ignored.
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11. We can only measure potential energy difference
We can measure the change in potential energy by comparing their positions and kinetic energies at two different times.
i is the initial time and f is the next time a measurement is taken
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12. Potential Energy Functions - C7
Electromagnetic Interaction
Gravitational Interaction
Potential Energy of a Spring
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13. Gravitational potential energy
One equation for the gravitational interaction potential energy
z is the distance measured vertically from a reference point
This equation is only valid close to the earth’s surface
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14. Negative Energy? Only true of Potential energy
Can be positive or negative with respect to a reference separation
Freedom to define reference separation
Kinetic energy is always positive
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15. Conservation of Energy – Hidden Forms
In future chapters, our equation for energy will include additional terms that represent energy transfers due to interactions.
One example is friction, it seems to remove energy from the system. It’s actually channeling the energy into hidden forms of energy that we can’t see, such as the vibration of individual atoms
Change in kinetic energy of particle 1
Change in kinetic energy of particle 2
Gravitational potential energy
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Hidden energy

16. Solving problems using framework
Translation
2 pictures – initial state and final state
Reference frame axes on each picture
Labels for masses, velocities and separations
Conceptual model diagram
Interaction diagram – like momentum
Include symbols inside system to show changes in kinetic and potential energies
Master equation
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17. Framework for Energy Problem – C6.2
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18. General Physics

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20. General Physics

21. Group Problems
C6S.5
C7B.2
C7S.3
Each group can go at their own pace to complete the problems.
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