Mechanics III Flashcards
what is the unit for work, W?
N*m=J
what component of force does work?
the component of force that acts in the same direction of displacement d
is work a vector or scalar?
it is a scalar value
what can the sign of work be or indicate?
positive work: work done by environment on object causing gain in kinetic energy, zero work: force acts perpendicular, negative work: work done by object on environment causing loss of kinetic energy
power
measures how fast work gets done
what is the unit for power?
J/s=W (watt)
energy
the ability to do work
kinetic energy
the energy of an object due to motion
is energy a vector or scalar?
energy is a scalar value
work-energy theorem
total work done on the object is equal to the change in its kinetic energy
potential energy
energy an object has by virtue of its position
change in gravitational potential energy is the opposite:
of the work done by the gravitational energy
what does a positive change in potential energy mean?
increased height of object
what does a negative change in potential energy mean?
decreased height of object
is potential energy absolute?
no, it is a relative quantity. it is the changes in potential energy that are important and physically meaningful
conservative force
independent of the path an object follows
what is an example of a conservative force?
gravity
nonconservative force
does depend on the path taken
what is an example of a nonconservative force?
friction
potential energy can only be defined for:
conservative forces
total mechanic energy, E
the sum of the object’s kinetic and potential energy
Conservation of Total Mechanical Energy
If the only forces acting on an object during its motion are conservative (no friction), then the object’s mechanical energy will remain the same throughout the motion
what happens if friction acts during an object’s motion?
the total mechanical energy is not conserved
mechanical advantage
quantity that describes how much less force is required when using that particular simple machine
how to calculate mechanical advantage (MA)?
resistance force/effort force=F without machine/F with machine=F out/F in
resistance force
the force that would be applied if no machine were being used
effort force
the force applied with the use of the machine
efficiency
measures the degree to which friction and other factors reduce the actual work output of the machine from its theoretical maximum
how to calculate percentage efficiency
W output/Energy input
how does an efficiency of less than 100% affect mechanical advantage?
the mechanical advantage will decrease
momentum, p
the product of mass and velocity, a vector
impulse
the change in moment, force applied for an interval of time
Law of Conservation of Momentum
in a system of interacting objects with no NET external force, then to total momentum of the system will remain constant and be conserved
p=mv and the Law of Conservation of Momentum is also known as:
linear momentum or the Law of Conservation of Linear Momentum
elastic collision
total momentum AND total kinetic energy are conserved
inelastic collision
total momentum is conserved but total kinetic energy is not
perfectly inelastic collision
an inelastic collision in which the objects stick together afterwards
angular momentum, L
must be defined relative to some reference point, =lmv, Iw (moment of inertia times angular velocity)
what is required for a greater desired change in momentum?
either a stronger applied force or a longer time interval in which the force is applied
force is also the rate of change of:
linear momentum p
torque is also the rate of change of:
angular momentum L
