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When does an object has energy
if it can produce a change in itself or in its surroundings.
- is the product of the net force exerted on an object and the distance the object moves in the direction of the force.
- W = Fd N·m = Joule (J)
- If force is at an angle: W = Fd cos θ (cos 90o = 0)
- Work is the transfer of energy by mechanical means. Energy is the ability to change an object.
Kinetic energy (KE):
energy an object has because of its motion.
Potential energy (PE):
energy an object has because of position, shape or form.
The net work done on an object is equal to its change in KE.
F = ma W = Fx W = max
- depends on the weight of the body and its separation from Earth.
- PE = mgh
How does PE depend on height?
- (Recall this equation: vf2 = vi2 + 2gx and multiply each term by ½ m)
- E = ½ mvf2 = ½ mvi2 + mgh
- If h = 0, then E = ½ mv2
- If v = 0, then E = mgh
- Total E = KE + PE
- Note: need a reference level to calculate PE
Elastic potential energy
is energy available for use when a deformed elastic object returns to its original configuration.
The sum of KE + PE = mechanical energy.
the Law of Conservation of Energy
- According to the Law of Conservation of Energy, the total energy of a closed, isolated system is constant.
- (If something is conserved, we mean it remains constant.)
- Energy can change form but the total energy does not change.
- Note: mechanical energy is not conserved in the presence of friction.
- is the rate of doing work or the rate at which energy is transferred.
- P = W/t J/s = Watt (W) P = Fd/t = Fv