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What is work?
- It is the means by which energy is transferred from one object or system to another.
- U = F(delta d)
- The unit of measurement is the Joule, J
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What is energy?
- In mechanics, energy is defined as the ability to do work.
- Energy comes in many forms: heat, light, sound, chemical, mechanical
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Kinetic Energy
- Energy due to motion
- A moving object has the ability to do work because of its motion.
- The unit of measurement is the Joule, J
- KE =1/2mv2
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Potential Energy
- Energy due to motion
- Two types: Gravitational and Strain Energy
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Gravitational Potential Energy (GPE)
- Potential energy due to an object's position relative to the earth.
- GPE of an object is related to its mass(m) and the height of the object (h)
- Unit of measurement is the Joule, J
- GPE = -mgh
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Strain Potential Energy
- Due to the deformation of an object.
- SPE of an object is related to its material properties (k) and the amount of deformation (x)
- The unit of measurement is the Joule, J
- SPE = 1/2kx2
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Work-Energy Relationship
- The unit of measure for work and energy is Joules.
- Work is the means by which energy is transferred from one object to another object.
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Demonstrating the Work-Energy Relationship
The work done equals the change in gravitational potential energy.
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Work-Energy Principle
- The work done by external forces (other than weight) acting on an object causes a change in energy of the object.
- U = delta E
- U = deltaKE + deltaGPE +deltaSPE
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Conservation of Mechanical Energy
When is Mechanical Energy Conserved?
- When no external forces, other than weight, act on the body.
- If there are no external forces, other than weight, acting on the body, NO WORK is done.
- If no work is done, the total mechanical energy of the object is conserved (i.e., it cannot be changed; it remains constant)
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Conservation of Mechanical Energy (2) continued...
- Thus, it can be used to analyze situations in which no work is done.
- For instance, in the pole fault, the vaulter does no work during the vault itself (i.e., once he or she leaves the ground)
- (KE + GPE + SPE) initial = (KE + GPE + SPE) final
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Power
- The rate of doing work or how much work is done in a specific amount of time.
- It can also be thought of as how quickly or slowly work is done.
- The unit of measurement is the Watt, W
- Power can also be defined as... average force times average velocity (Fv) along the line of action of that force.
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