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19 Cards in this Set
- Front
- Back
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work
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(scalar) the result of a force exerted over a distance as an object moves
*if an object does not move, no work is done! - measured in Newton*meters = Joules (J) - generally W=Fapp*displacement - net work (Wnet) = Fnet*displacement |
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energy
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- the ability to do work
- measured in Joules (J) - comes in different forms... mechanical, thermal, kinetic, electrical, light, etc... |
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law of conservation of energy
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energy cannot be created or destroyed, only transferred from one form to another
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mechanical energy
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sum of potential and kinetic energy in a system
Em = Ep + Ek |
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potential energy
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energy of an object because of its position
depends on force acting on object and displacement/position of the object Ep = Fd |
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gravitational potential energy
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potential energy of an object due to it's position above the Earth's surface
*depend on reference point chosen! Ep = Fd Ep = mgh |
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when lifting an object at a constant velocity...
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- work done = change in gravitational potential energy
Fnet = 0N Fnet = Fapp + Fg Fapp = -Fg W = Fappd = -Fgd = -mgh |
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elastic potential energy
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energy stored when an objects shape is changed from its standard shape without being permanently deformed
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Hooke's Law
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- stretch produced by a force applied to a spring is proportional to the magnitude of the force.
- applies to any elastic substance when a force is exerted upon it Fαx F = kx |
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potential energy of a spring
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Ep = Fd F = kx
Fave = Fmax/2 = kx/2 Ep = 1/2kx2 |
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kinetic energy
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(scalar) energy of motion (J)
Ek = 1/2mv2 as... Ek α m [and] Ek α v2 |
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work energy theorem
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"the net work done on an object is equal to its change in kinetic energy
Wnet = ∆Ek Since net work is a product of the net force and displacement. Fnet d = EKf – Eke Fnet d = 1⁄2 mv 2 – 1⁄2 mv 2 *want to change kinetic energy, increase net force or increase distance over which the force acts (ex. follow through, crumple zone) |
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isolated system
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- group of objects completely isolated from all objects outside the system
- no matter or energy enters or leaves the system - no force from outside the system may work to transfer any energy to or from any object inside the system |
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conservative forces
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when work is done against a conservative force, the energy expended in doing the work is stored and recoverable.
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non-conservative forces
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when work is done against a non-conservative force, the expended energy is not recoverable, but is converted to thermal energy.
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law of conservation of mechanical energy (no friction)
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Em = Ep + Ek
for an object moving in a frictionless system mechanical energy is conserved . Em(before) = Em (after) if the only forces acting on an object are conservative forces the mechanical remans constant. |
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law of conservation of mechanical energy (friction)
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- in reality, no energy transformation is 100% efficient!
- energy "lost" is considered work done by friction |
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power
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- rate at which work is done
- measured in Watts (W) (J/s) |
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efficiency
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calculating efficiency of energy transformation; output/input x* 100
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