Machines Ch' 7

1
Machines - Ch. 7

• II. The Simple Machines
• (p.180-183)

• Lever
• Pulley
• Wheel Axle

• Inclined Plane
• Screw
• Wedge

2
A. Lever

• Lever
• a bar that is free to pivot about a fixed point,
  or fulcrum

3
A. Lever

• Ideal Mechanical Advantage (IMA)
• frictionless machine

• Le must be greater than Lr in order to multiply
  the force.

4
A. Lever

• First Class Lever
• can increase force, distance, or neither
• changes direction of force

5
A. Lever

• Second Class Lever
• always increases force

6
A. Lever

• Third Class Levers
• always increases distance

7
B. Pulley

• Pulley
• grooved wheel with a rope or chain running along
  the groove
• a flexible first-class lever

F
Le
Lr
8
B. Pulley

• Ideal Mechanical Advantage (IMA)
• equal to the number of supporting ropes

IMA 0
IMA 1
IMA 2
9
B. Pulley

• Fixed Pulley

• IMA 1
• does not increase force
• changes direction of force

10
B. Pulley

• Movable Pulley

• IMA 2
• increases force
• doesnt change direction

11
B. Pulley

• Block Tackle

• combination of fixed movable pulleys
• increases force (IMA 4)
• may or may not change direction

12
C. Wheel and Axle

• Wheel and Axle
• two wheels of different sizes that rotate
  together
• a pair of rotating levers

Wheel
Axle
13
C. Wheel and Axle

• Ideal Mechanical Advantage (IMA)
• effort force is usu. applied to wheel
• axle moves less distance but with greater force

14
Problems

• You use a 160 cm plank to lift a large rock. If
  the rock is 20 cm from the fulcrum, what is the
  planks IMA?

GIVEN Lr 20 cm Le 140 cm IMA ?
WORK IMA Le Lr IMA (140 cm) (20 cm) IMA
7
15
Problems

• A crank on a pasta maker has a radius of 20 cm.
  The turning shaft has a radius of 5 cm. What is
  the IMA of this wheel and axle?

GIVEN re 20 cm rr 5 cm IMA ?
WORK IMA re rr IMA (20 cm) (5 cm) IMA 4
16
Problems

• A steering wheel requires a mechanical advantage
  of 6. What radius does the wheel need to have if
  the steering column has a radius of 4 cm?

GIVEN IMA 6 re ? rr 4 cm
WORK re IMA rr re (6)(4 cm) re 24 cm
re
rr
17
Problems

• You need to lift a 150 N box using only 15 N of
  force. How long does the lever need to be if the
  resistance arm is 0.3m?

GIVEN Fr 150 N Fe 15 N Lr 0.3 m Le ? MA
10
WORK Le IMA Lr Le (10)(0.3) Le 3 m Total
length Le Lr Total length 3.3 m