transfer kinetic energy (the energy of motion) reduce the effort needed to move a load
DESCRIPTION
Simple Machines are used to:. Transfer kinetic energy (the energy of motion) Reduce the effort needed to move a load Change the direction or amount of motion Change the type of motion (rotary to straight line). Key Terms:. Effort (E) = the input force - PowerPoint PPT PresentationTRANSCRIPT
• Transfer kinetic energy (the energy of motion)
• Reduce the effort needed to move a load
• Change the direction or amount of motion
• Change the type of motion (rotary to straight line)
• Effort (E) = the input force• Either the user or some type of engine
supplies this force.
• Load (R) = the output force. • Also known as the force resisting the
motion.
• Mechanical Advantage (MA) = a measure of how much effort is decreased by the simple machine.
Mechanical Advantage = Load Effort
MA = R
E
• Work : The force applied on an object times the distance traveled by the object.
Work = (Force)Distance = (F)dStarting Position
Force
Finishing Position
Distance
• Friction results from two bodies moving against each other in different directions. – Friction always opposes motion and makes doing work harder. – Lubricants (graphite, oil, grease, silicone) and bearings are used to
combat friction.– Sometimes, friction is a good thing!
• Efficiency is the ratio of the work that results to the amount of work put into the machine.
Power is the rate at which work is performed.
Energy describes the amount of work that can be performed by a force.
P=W
tE=W
P = power
W = work
t = time
E = energy
•A lever is a stiff bar which rotates around a point called the fulcrum. •The forces on the lever are the Effort (E) and the load (R).
E = EffortR = LoadLE = Length (distance) from fulcrum to EffortLR = Length (distance) from fulcrum to Load (R)
Moment = Force x distance to fulcrum
CW (-) CCW (+)
The Effort is positive because it is rotating in a counter clock wise rotation around the fulcrum.
The Load is negative because it is rotating in a clock wise rotation around the fulcrum.
Moment 1 = Moment 2
Force 1 x distance 1 = Force 2 x distance 2
300 lb x 4 ft = 1200 lb x 1 ft
1200 ft-lb = 1200 ft-lb
Mechanical Advantage =Load Effort
MA = LE
LR
=1200 lb
300 lb= 4
=4 ft
1 ft= 4
RE
LE
LR= or LE(E) = LR(R)
R E=
• You are given a board that is 8 feet long and a rock to use as a fulcrum and you need to lift a heavy object. Where would you place the rock? Why?
LE becomes very large.
LR becomes very small.Place the rock as close as
possible to the load
If LE greater than LR, then MA greater than 1
If LE less than LR, then MA less than 1
Since LE greater than LR, then MA greater than 1
Since the LE less than LR, then MA less than 1
Given: LE = 6 ft, LR = 3 ft, E = 1 lb Find R.
Solution:LE R
LR E= =6 ft
3 ft= 2 So.. 2 =
R
1lb = 2 lb
Given: R = 8 lb , LE = 4 ft , E = 4 lb Find LR.
Solution:
LE R
LR E= =4 ft
LR =8 lb
4 lb= LR= 2 ft
Mechanical Advantage =Load Effort
MA = Radius to Effort
Radius to Load =LE
LR
• A wheel with a 12 inch radius is used to turn an axle with a radius .5 inches. What is the mechanical advantage?
MA = Radius to Effort
Radius to Load =LE
LR
MA = Radius of Wheel
Radius of Axel =12 in
.5 in = 24
• Consider an axle used to drive the wheels of a car. The wheel radius is 12 inches, while the axle radius is 1 inch. What is the mechanical advantage?
MA = Radius to Effort
Radius to Load =LE
LR
MA = Radius of Axle
Radius of Wheel =1in
12 in = 0.083
You need to know the Circumference of Wheel
S
S = Distance traveled in one revolution
C = (Π)Wheel Diameter = (3.14)D
• If your car has tires with a diameter of 24 inches how many times will the tires rotate if the car travels 100 feet?
C = (Π)Wheel Diameter = (3.14)2 ft = 6.28 ft.
24 inches = 2 feet
100 ft
6.28 ft
S = Distance traveled in one revolution = 6.28 ft
Number of Revolutions = = 15.9 revolutions
Work at Effort end = Work at Load end
(Effort) Dist. traveled by rope = (Load) Dist. moved by Load
MA = The number of strands supporting the load. (The end strand ONLY counts when the effort is pointing upward.)
Fixed Pulley Movable
Pulley
Block & Tackle
MA = 1MA = 2 MA = 4
The pulley system shown is used to lift a load of 60 lbs a distance of 2’. How much effort must be applied, and how much rope do you need to pull?
MA = # of strands = 6
6 = R
E =60 lb
E
Effort = 10 lb
Distance traveled = 2 ft * 6Distance traveled = 12 ft
R or Load E or Effort
MA = R
E
The Effort is parallel to the Inclined Plane.
The Load is 900 to the ground. Or in the direction of gravity.
H or Height of Inclined PlaneL or Length of In
clined Plane
MA = L
H
The Length is how long the Inclined Plane is.
The Height is vertical distance between the starting point and ending point.
• In the diagram below, L = 24 inches, H = 6 inches and the Effort = 60 lb
• Find the mechanical advantage and the maximum load that can be moved.
• What is the tradeoff for reducing the effort?
A
B
H
L
R
E
A
B
H
L
R
E
MA = L 24 in
H 6 in= = 4
Mechanical Advantage =Load Effort
4 =Load
30 lb
Load = 120 lb
In order to move the 120 lb 6 inches off the ground, we need to travel a distance of 24 inches along the incline.
Effort
Inclined Plane
Effort
Wedge
Single
LH
Double
L
H
Mechanical Advantage =Load Effort
MA = L
H
• Find the mechanical advantage and the maximum separation load for a wedge with an incline length of 10 inches, an overall height of 4 inches, and which is exerting an effort of 100 pounds.
Effor
t
MA = L
H =10 in
4 in = 2.5
Mechanical Advantage =Load Effort
2.5 =Load
100 lb = Load = 250 lb
• 1/4 - 20 UNC
1/4 = the outer diameter of the threads.
20 = the number of threads per inch of screw length.
UNC refers to Unified National Coarse thread.
OD
1in.
Number of Threads per Inch
View A
View APitch
Pitch =
Number of Threads per Inch
1in.
Mechanical Advantage =Load Effort
MA =Circumference
Pitch=
C
P
• A screw with 18 threads per inch is turned by a screwdriver having a handle diameter of 1 inch. What is the mechanical advantage of the screw?
MA =Circumference
Pitch=
C
P
Pitch =
Circumference = (3.14) 1 in = 3.14 in
1 in
18= 0.055 in
MA =Circumference
Pitch=
C
P=
3.14 in
0.055 in= 57.09