Work, energy and power Flashcards
Work (mathematical relationships)
F Δx cosϴ, Where: -F is the magnitude of the force -Δx is the magnitude of displacement -ϴ is the angle between the force and the displacement
Positive net/total work
Energy is transferred to the object in the direction of original displacement
increase an object’s kinetic energy
What happens when work is done on a system?
What is the effect of work done on abject by a force?
work done = energy transferred
- Energy is transferred from one object to another object (energy is transfers within a system)
- The amount of work done by a force is equal to the energy transfer taking place
When is positive work done on an object?
When ϴ is less than 90°
cos 0 = 1
cos 90 = 0
this will mean that the force (or at least a component if it ) acts in the direction of the initial displacement of the object
Zero work
Done on object by a force that acts at 90° to the direction of object’s displacement
Energy of object remains unchanged
When do we get negative work
When ϴ is more than 90°
cos 180 = - 1
Negative
Done by a force which acts against the motion of the object
Energy is removed from the system/object and transferred to other forms of energy
Work (explained in words)
Work is done when a force acts on an object and it moves in the direction of the force.
Work done is equivalent to the energy transferred
Net work (mathematical relationships) 2 methods
Calculated by adding positive and negative work done by each force
- W net = Σ W of individual forces
(We add the work done by each force algebraically since work is a scalar quantity)
OR - W net = F net Δx cosϴ
Work unit analysis
Joules
(Recall: Work done is equivalent to the energy transferred)
Work is a scalar quantity as energy does not have direction
Gravitational potential energy
Energy of an object due to its position in a gravitational field relative to a reference point
(reference point is usually the surface of the earth)
Potential energy (unit analsis)
The energy possessed by an object because of its position relative to other objects
Ep = mgh
units: Joules
Kinetic energy
Energy of an object because of its motion
Ek = 1/2 mv^2
units: joules
Mechanical energy
Em = Ep + Ek Em = mgh + 1/2 mv^2
The sum of (gravitational) potential energy and kinetic energy
Law/principle of the conservation of mechanical energy
Σ Em initial = Σ Em final
Eki + Epi = Ekf + Epf
Total mechanical energy, as the sum of Ep and Ek, in an isolated system remains constant
(no non-conservative forces present > only gravitational potential force allowed to be included in system as it is a conservative force)
