Note Guide- Ch.5- Machines
machine-
input force/workoutput force/work-
input force
output force
*There are 3 ways that machines make work easier:
1)
input force distance
output force
distance
2)
input force
distance
output
force
distance
input force
distance
output force
3)
distance
mechanical advantage (MA)Mechanical Advantage = Output Force
Input Force
Example 1: If an input force of 10 N is needed to turn use a can opener and the
output force of this machine is 50 N, then the MA is .
MA =
(output force)
MA =
(input force)
Example 2: If sweeping requires an input force of 15 N and the output force is 5 N,
then the MA is .
MA =
(output)
MA =
(input)
Example 3: If just changing direction (like opening and automatic door), the input force
of 30 N and the output force of 30 N would be the same so the MA would be
MA =
MA =
*work transfers energy
efficiency-
*an ideal machine would have an efficiency of 100%, but because all machines have friction,
work output can never = work input so a machine that is 100% efficient DOES NOT EXIST!
Calculating efficiency:
Efficiency (%) =
x 100
*remember that work is measured in joules (J)
example: If I’m lifting a very big box of marbles from the ground to my classroom window
and I put in 700 J of work and 550 J of work are done on the box, what would the
efficiency be?
Efficiency =
x 100 = %
*the more moving parts a machine has, the less efficient it is because there are more parts
causing friction, taking energy away from the system
*one of the best ways to improve the efficiency of a machine is to reduce friction
simple machines1)
2)
3)
4)
5)
6)
lever-
(seesaw is an example)
fulcrum-
*with a lever, the output force can be thought of as resistance
output
output
input
force
force
force
input
force
example:
input
force
output
force
wheel & axle:
wheel
axle
example: screwdriver, steering wheel, doorknobs, electric fans
pulley1) fixed pulley-
2) movable pulley-
3) pulley system-
fixed pulley
MA = 1
movable pulley
MA = 2
pulley system
MA = 2
pulley system
MA = 3
inclined plane-
inclined plane
wedgethick edge
thin edge
*wedge is like a doubled inclined plane except it usually moves (an inclined plane does not usually
move, things move on it)
screw-
ideal mechanical advantage (IMA)-
To calculate the ideal mechanical advantage (IMA) of:
1) inclined plane:
IMA =
IMA = l
h
IMA = 2
1
IMA = 1
example: If a ramp is 2 m long (the incline) and 1 m high, the IMA would be 1.
2) wheel & axle:
IMA =
IMA = Rin
Rout
IMA = 30 cm
5 cm
IMA = 6
example: If the radius of the steering wheel was 30 cm and the radius of the steering
column was 5 cm, the IMA would be 6.
3) lever:
IMA =
IMA = din
dout
IMA = 40cm
IMA = 8
5 cm
example: If the distance from input to fulcrum of a crow bar was 40 cm and the output
to fulcrum was 5 cm, the IMA would be 8.
compound machinepulley
lever
wheel & axle
gear*to find the MA of a compound machine, you add the MA of all the simple machines that
compose the compound machine
microtechnologynanotechnology-
robot-