Actual Mechanical advantage The ratio of force to overcome large resistance to the force applied Friction is taken into account
F AMA= o force overcome(r esistance) force applied F i force output of the machine force input to the machine
2
Ideal mechanical advantage (IMA) The ratio of the distance moved by the effort to the distance moved by the load s
i IMA s o
distance moved by the effort distance moved by the load 3
Efficiency
power output Efficiency (%) 100 % power input work output Efficiency (%) 100 % work input MA Efficiency (%) 100 % VR AMA Efficiency (%) 100 % IMA
4
Principle of Work • Input Work = Output Work + Energy dissipated by Friction • Friction neglected then output = input work work
5
The simple machines 1. Lever 2. Inclined plane 3. Pulley looked upon as 4. Wheel and axle modified levers 5. Gear 6. Wedge Adaptations of 7. Screw the incline plane
Simple machine can be found in many transportation devices
7
8
Helps lift heavy weights using longer distances
9
Inclined planes make the work of moving things easier Makes it easier to move objects upward; a longer path, but easier lifting
10
Pulley, wheel and axle
11
Pulleys are used in a number of applications including: Elevators Cranes Automobiles
12
Gears are toothed wheels which interlock to form simple machines. The tighter the joint, the less chance of slipping Driver
Driven
13
Wedge Two inclined planes joined back to back. Wedges are used to split things.
14
A screw is an inclined plane wrapped around a shaft or cylinder.
15
Pulley • consists of a grooved wheel on an axle • with a cord or rope passed around the groove Two kinds of pulley • fixed pulley • movable pulley 16
Movable pulley Fixed pulley 17
Fo=2Fi
Load=effort Fo=Fi
18
19
P P
P=?
w=1000 N
20
( ? ) lb
1000 lb
( ? ) lb
( ? ) lb
IMA = 2
21
? ? T
? ?
T
IMA=2 IMA=3 IMA=4 IMA=5
22
IMA= 8
23
IMA = no. of ropes supported by load 24
Single fixed pulley By the 1st condition of Equilibrium ∑Fy=o
Fi - Fo=0
Fi = Fo , F o 1 F i AMA 1 Friction is neglected,AMA=IMA=1 25
Single fixed pulley • By the 1st condition of equilibrium ∑Fy=0 2Fi - Fo=0 F AMA o 2 F i
Friction is neglected, IMA = AMA IMA = 2
Two moveable pulleys • By the 1st condition of equilibrium
∑Fy=0 3Fi - Fo= 0 F AMA o 3 F i
Fi
Friction is neglected, IMA = AMA IMA = 3 27
Two moveable pulleys By the 1st condition of equilibrium,
∑Fy=0 4Fi - Fo=0
Fi
Fi Fi F
i
F AMA o 4 F i
Fi
Friction is neglected, IMA = AMA IMA = 4
W
Fo
28
1. (i) IMA ?, s i 3.3m, s o 8cm 8 x 10m si
ii
3.3 IMA 2 so 8 x 10
41.25
Efficiency 60 %, AMA ? Efficiency
60 %
AMA IMA AMA
41.25
AMA 24.75
X 100 %
X 100 %
29
iii
Fo ?, Fi 50N, If Efficiency 60 %, AMA 24.75 AMA
