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Every physical process that occurs in the universe involves energy and energy ________ or _______. The energy approach to describing motion is particularly useful when the force is not _______
- transfers or transformations
- constant
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What are the 6 forms of energy?
What are the three subcategories
- Mechanical Energy: Kinetic Energy (K), Gravitational Potential Energy (Ug), Elastic or Spring Potential Energy (Us)
- Thermal Energy: (Eth)
- Other: Chemical Energy (Echem) and Nuclear Energy (Enuclear)
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Explain each Mechanical Energy
- Kinetic Energy: the energy of motion. All moving objects have kinetic energy. The heavier and faster an object the more kinetic energy it has
- Gravitation Potential Energy (Ug): Stored energy associated with an object's height above the ground. As the coaster ascends, energy is stored as gravitational potential energy. As it descends, this stored energy is converted into kinetic energy
- Elastic or Spring Potential Energy (Us): the energy stored when a spring or other elastic object, such as this archer's bow, is stretched. This energy can later be transformed into kinetic energy of the arrow
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Explain Thermal, Chemical and Nuclear Energy
- Thermal Energy (Eth): Hot objects have more thermal energy than cold ones because the molecules in a hot object jiggle around more than those in a cold object. Thermal energy is the sum of microscopic kinetic and potential energies of all molecules in an object. In boiling water, some molecules have enough energy to escape the water as steam
- Chemical Energy (Echem): Electric forces cause atoms to bind together to make molecules. Energy can be stored in these bonds, energy that can later be released as the bonds are rearranged during chemical reactions. When we burn fuel to run our car or eat food to power our bodies, we are using chemical energy
- Nuclear Energy (Enuclear): An enormous amount of energy is stored in the nucleus, the tiny core of an atom. Certain nuclei can be made to break apart, releasing some of this nuclear energy, which is transformed into the kinetic energy of the fragments and then into thermal energy. The blue glow of a nuclear reactor is from from high energy fragments as they travel through water
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Define system
System: a simplified model that focuses on a small portion of the universe and ignores details of the rest of the universe (environment)
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Identifying a system:
State four possible characteristics of a valid system
- A valid system may:
- be a single object or particle
- be a collection of objects or particles
- be a region of space
- vary with time in size and shape
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There is a system boundary around the system. Explain this boundary and how the system relates to work
- The boundary can be an imaginary surface, not necessarily a physical boundary. The boundary divides the system from the environment
- Work is a mechanism for transferring energy into a system
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Describe the Basic Energy Model
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Energy transfer is an exchange of energy between _______ and _______. Energy enters the system as ______ and leaves the system as _______
- system and environment
- work
- heat
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Name and define the two primary energy transfer processes
- Work: Mechanical transfer of energy to or from a system by pushing or pulling on it
- Heat: nonmechanical transfer of energy from the environment to the system (or vice versa) because of a temperature difference between the two
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What is the formula for work done by a force at an angle that causes displacement of an object?
 - *parallel to the displacement
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A constant force has moved a particle -> work, W was done by the force (environment) on the particle (system). State the formula and explain each component
- W ☰ (Fd)(cosθ)
- W = work done on a system by external agent
- F = magnitude of a constant force exerted by external agent
- d = displacement of the point of application of the force
- θ = angle between the force and the displacement vectors (cosθ determines the sign of W)
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What are two situations in which the force does NO work on the object? What manner of force are we specifically focused on in this scenario?
- If displacement is zero
- The force applied is perpendicular to the displacement of its point of application (i.e. θ= 90°)
- We are only concerned with the component of the force that is parallel or anti-parallel to the displacement aka Fcosθ
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Work is a ______ quantity, it can be either ______ or _______. When an object is lifted, the work done by the applied force on the object is _______ (why?). As an object is lifted, the work done by the gravitational force on the object is _______. What are the units of work (2)
- scalar quantity
- positive or negative
- positive because the direction of that force is upward, in the same direction as the displacement
- negative
- 1 Joule (J) = 1 N*m
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Kinetic energy is the energy of a particle due to its ______. What is the formula and units
- motion
- K ☰ 1/2mv2
- m: mass of particle
- v: speed of the particle
- Unit: joule (J)
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Define and state formula/breakdown and units: Rotational kinetic energy
- Krot ☰ (1/2)(Iω2)
- I: moment of inertia of the object
- ω: angular speed of the object
- Unit: Joule (J)
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Total kinetic energy of a rolling object depends on which two values
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When work is done on a system and the only change in the system is in its speed, the net work done on the system equals:
Work-kinetic energy theorem only depends on ______ and ______ points for the ______, it does not depend on details of the ____ between the end points
- The change in kinetic energy of the system
- initial and final points
- speed
- path
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When work is done on a system by a net force ΣF and the only change in the system is its speed, then the work done by a net force on a particle equals the change in its ________ energy.
If Wnet force > 0, energy transfers to ______, kinetic energy ______ or speed _______.
If Wnet force < 0, energy transfer from _______, kinetic energy ______ or speed _______
- kinetic energy: Wnet force = Kf - Ki = ΔK (Work-Kinetic energy Theorem)
- system
- increases
- increases
- system
- decreases
- decreases
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Potential energy is the energy an object has by virtue of its ______. Consider a book lifted up from the surface of a table (y=yi) to a final height of yf at a constant speed, state the formula for work done.
When it is held above the table it has ______ energy due to its position. If released, the book will fall, converting this potential energy to the ______ energy of motion
- position
 - stored energy
- kinetic energy
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Interaction forces that can store useful energy as potential energy are called ______ forces. What are their two equivalent properties
- conservative forces:
- The work done by a conservative force on a particle moving between any two points is independent of the path taken by the particle
- The work done by a conservative force on a particle moving through any closed path is zero
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Define Non conservative force and state 2 characteristics
- Non-conservative force: a force that does not satisfy properties 1 and 2 for conservative forces
- 1) Work done by a non-conservative force is path dependent
- 2) When moving through any closed path, the work done is greater than zero
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State classic examples for conservative forces and non conservative forces
- Conservative forces: Gravitational and Spring Force
- Non-conservative forces: Frictional force
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State the formula for net force and work done define gravitational potential energy (identity equation) and the formula for work done
*keep in mind it falls at constant speed
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Gravitational potential energy only depends on _______ ________, it is path __________. A reference configuration for y= 0 is required. Convention reference for Ug = 0 is on the _____ _____. The unit is the ______
- vertical position
- independent
- Earth's surface
- Joule
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State the formulas for net force, integral for Work, the formula for Elastic potential energy and for work done
*also at constant speed
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Elastic potential energy is the energy stored in the _______ _______, it depends on how much length is displaced from ________ position: A reference configuration for x = 0 is at _______ position. Spring can be either stretched (x __ 0) or compressed (x __ 0). Us is always a _______ value
- deformed spring
- equilibrium position
- equilibrium position
- x>0 and x<0
- positive
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Formula for the sum of the kinetic and potential energies of a system
Emech ☰ K + U
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What are the kinetic, potential and total energy breakdowns of these scenarios
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Thermal energy is the energy associated with the temperature of a system. If a book slides across a surface, _______ does work and ________ the internal energy of the surface
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Work is a ______ mechanism for energy.
_____ + ____ = ΔE system
____ = ΔE th
- transformation
- ΔK + ΔEth =ΔEsystem
- fkd = ΔEth
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State the work equivalents for (6):
Gravitational force*
Tension force
Normal force
Frictional force*
Spring force *
Applied force*
Wall forces*
Wall other forces
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Explain the concept of energy being conserved
- This means that energy cannot be created or destroyed
- If the total amount of energy in a system changes, it can only be due to the fact that energy has crossed the boundary of the system by some method of energy transfer
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Define isolated system and state the equation for change in the system's energy:
- Isolated system: no energy crosses the system boundary by any method
- ΔEsystem = ΔK +ΔKrot +ΔU + ΔEint +... = 0
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_______ energy is conserved for isolated system with non conservative forces (such as ______) acting:
ΔEmech = ?
- Mechanical energy
- friction
- ΔEmech = ΔK + ΔKrot + ΔU
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Label the diagram
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In a non-isolated system ______ crosses boundary of the system due to interaction with the _________. For example, interaction of system with environment is work done by _______ force. What is the formula for work done by all other forces?
- energy
- environment
- external
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Problem solving strategy for Isolated System (3-story)
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Kinetic energy K is energy of ______
Potential energy U is energy of ______
Thermal energy Eth is energy associated with _______
System energy E = ?
- motion
- position
- temperature
- E = K + U + Eth + Echem +......
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Label the diagram (for the top, how does the environment relate to the syste)
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Name 2 things power measures and state the corresponding formulas
When energy is transferred due to a force F acting on an object moving at velocity v, the formula for power is:
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What is the SI unit of power:
How many in 1 horsepower
How many in 1 Kilowatt-hour
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Consider a system of 2 masses (isolated system). Two particles which interact obey Newton's third law F1on2 = -F2on1
How can we express this (3-story)
The sum of the product of masses and velocities for a particles in an isolated system is _______
 - aka For isolated system: the sum of all momentum (Σpi) must be equal to a constant
- aka: m1v1 + m2v2 + m3v3.... = constant
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