Simple Machines Device that makes doing work easier is a machine Machines increase applied force and/or change direction of applied force to make work.
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Simple Machines•Device that makes doing work easier is a machine
•Machines increase applied force and/or change direction of applied force to make work easier
Effort and Resistance
•Force applied to machine is effort force
•Resistance force – force applied by machine to overcome resistance
Energy and Simple Machines
•Amount of energy the machine transfers to the object cannot be greater than the amount of energy transferred to the machine
Energy and Simple Machines
•An ideal machine with no friction would have the same input work and output work
•Some energy transferred is changed to heat due to friction
Mechanical Advantage
•The number of times a machine multiplies the effort force.
Efficiency•Measure of how much of
the work put into a machine is changed into useful output work by the machine.
Lever
•Bar that is free to pivot about a fixed point called the fulcrum
•MA of lever depends on the placement of the fulcrum
Simple MachinesWhich lever will allow the weight to be lifted
with the least amount of force?
It is easier to lift a weight when the fulcrum is closer to the weight being lifted.
fulcrum fulcrum
Simple Machines
fulcrum
200 g100 g
Below is a picture of a perfectly balanced system. Describe how mass affects the
distance from the fulcrum.
The greater mass is closer to the fulcrum.Notice that is twice as big and half as close.
We always measure to the center of mass.
Pulley•Grooved wheel with a rope
or cable running along a groove
The greater the number of times the cable wraps around the pulleys, the greater the MA.
Simple MachinesWhich pulley system will allow the weight to
be lifted with the least amount of force?
Moveable pulleys, often grouped together in block and tackle systems,
reduce the amount of force needed to lift an object.
Block and
Tackle
Wheel and axle
•Machine with two wheels of different sizes rotating together
Simple Machines
Gears are a type of simple machine. While
it takes less force to spin the larger wheel,
the smaller wheel spins at a faster rate.
Inclined Plane
•Sloping surface that reduces the amount of force required to do work
Simple MachinesWhich ramp would it be easiest to slide a box
up to the given height?
Making ramps longer lowers the amount of force needed to move an object up the ramp.
Wedge
•Inclined plane with one or two sloping sides
Screw
•Inclined plane wrapped in a spiral around a cylindrical post
Compound machine
•Uses a combination of two or more simple machines
EfficiencyThe efficiency of machines can be determined by using
a simple formula found on the formula chart.
Machines are always less than 100% efficient because of the force that opposes motion between
the parts of the machine. What force is it that opposes this motion?
Friction opposes the motion in the machines. Friction converts the machine’s work into heat.
Formulas
W = F x d
Vf = Vi + at
d = Vi t + ½ at2
2ad = Vf2 – Vi2
d = ½ (Vf + Vi) t
KE = ½mv2
GPE = mgh
ME = KE + PE
P = Work/t
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