Chapter 14Lesson 4

The Simple Machine

I. Lever System

A. Def – A lever is a bar that is free to pivot or turn about a fixed point.

B. Parts of a lever1. Fulcrum – fixed point of the lever2. Effort arm – part where force is applied to the lever.3. Resistance arm – part where the resistance is found on the lever.

C. Ideal Mechanical Advantage1. IMA = Length of effort arm

Length of resistance arm

or Le

Lr

2. Ex: A worker uses an iron bar to raise a manhole cover weighing 65 N. The effort arm of the lever is 60 cm long. The resistance arm is 10 cm long. What is the ideal mechanical advantage of the bar?Le =

Lr =

= 6 (IMA)

60 cm

10 cm

D. Types of Levers1. 1st Class

-E – F – R-Common Ex: teeter totter scissors pliers claw of hammer

2. 2nd Class- F – R – E- Common Ex: stapler bottle opener wheelbarrow nut cracker

3. 3rd Class (increase speed)- F – E – R - Common Ex: fishing rod tweezers mousetrap baseball bat softball bat

II. Pulleys

A. Def – a grooved wheel with a rope or chain running along the groove.1. similar to 1st class lever2. uses rope instead of bar3. has effort arm and resistance arm.

B. Types of Pulleys1. Fixed -Fixed – pulley does not move

-MA = 1 2. Movable -Movable – pulley is movable -MA = 2 (can vary)

3. Block and Tackle-uses fixed and movable-Large Mechanical advantage-MA = # of ropes inthe pulley system-MA = 2

What is the MA? = 4

III. Wheel and Axle

A. Def – a simple machine consisting of 2 different sized wheels that rotate together.1. Parts

-small wheel = axle2. Effort force is applied to large wheel3. Large wheel turns the axle4. IMA = rw / ra

5. Ex: Bike, doorknobs, ice cream makers, cars…

6. Ex: An ice cream maker has a wheel radius of 20cm. The axle has a radius of 15 cm. What is the ideal mechanical advantage of the wheel and axle?20 / 15 =1.3 IMA

IV. Inclined Plane, Wedge, Screw

A. Inclined Plane1. Def – a sloped surface used to raise objects2. IMA = length of slope / height of slope

3. Ex: any ramp4. Remember** Force is smaller but distance is greater.

B. Screw1. Def – Inclined plane wrapped in a spiral cylindrical post.2. Ex: screws, lids, drill bits

C. Wedge1. Def – Inclined plane with 1 or 2 sloping sides2. Used to cut or split3. Ex: knives, ax blades, chisels…