• 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