weight of block = _____________________
Force (FA) = hanging mass × 9.8
= _______________ × 9.8 = _______________
Height = _______________ Length = _______________
(For all calculations, mg = the weight of the block.)
Part I – Calculate µstart and µslide by using:
µ = FA / mg (4 times)
Part II – Calculate µ by using:
µ = Height / Length (2 times)
Part III – Calculate µ by using:
1) Height / Length, then shift tan to get θ
2) FA – mg sin θ – µmg cos θ = ma
list all the µ’s you calculated in table form
1) How did µstart compare to µslide? How should it? (Part I)
2 )How did surface area affect friction? How should it? (Parts I & II)
3) Which method was most accurate? Why? (discuss errors)
Machines – make work easier by multiplying the applied force (but the lifter must move a farther distance).
Resistance = R = the weight being lifted
Effort = E = the force being applied
IMA = ideal mechanical advantage – the theoretical maximum multiplier a machine can provide (if the machine works perfectly with no friction). It depends on the way the machine is constructed.
|IMA = Length / Height|
|= L / H|
|IMA = Earm / Rarm|
Pulleys IMA = # of support segments (all segments count except for an outside one pointing down)
|I = 1|
|II = 3|
|III = 3|
|IV = 4|
The IMA tells how much further the lifter (effort) has to move, compared to how far the weight (resistance) moves.
AMA = actual mechanical advantage = actual multiplier the machine provides. This must be determined by experiment.
*** The AMA must be < the IMA because friction causes some of the energy to be converted into heat.
Efficiency – tells how well the machine works
|× 100||(units = %)|
*** The Efficiency must be < 100% due to energy loss caused by friction.
For the lever shown, 5.0 N of force is used to lift a 10 N object. Find the AMA, IMA and Efficiency of the machine. If the weight is to be lifted a distance of 2.0 m, how far would the Effort have to move?
IMA = Earm / Rarm = 12 / 4.0 = 3.0
AMA = R / E = 10 / 5.0 = 2.0
Efficiency = AMA / IMA × 100 = 2.0 / 3.0 × 100
Efficiency = 6.7 × 101 %
IMA = Edist / Rdist
3.0 = Edist / 2.0 m
Edist = 6.0 m