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Simple Machines

Simple Machines

• make effort easier

• changes direction or magnitude of force applied for work

Compound Machines

multiple simple machines working together

6 Simple Machines

• Inclined Plane

• Wedge

• Lever

• Pulley

• Screw

• Wheel and Axle

Inclined Plane

Stationary, flat surface set at angle

• as distance of slope increases, force decreases, greater mechanical advantage

Ex:

• ramp

• ladder

• staircase

SLOPE IS MECH ADVANTAGE

Wedge

Moving inclined plane that moves through a load

• thinner the wedge, bigger the mechanical advantage

SLOPE IS MECH ADVANTAGE

1st Class Lever

fulcrum between effort and load

• fulcrum midpoint: no advantage

• fulcrum close to effort: distance amplified

• fulcrum close to load: effort amplified

2nd Class Lever

load between fulcrum and effort

• load closer to fulcrum, increased mech advantage

• effort force is amplified

Ex:

Wheelbarrow

3rd Class Lever

effort between load and fulcrum

• moves load over longer distances and reduces effort

Ex:

Baseball bat

fishing rod

Wheel and Axle

a simple machine consisting of two circular objects of different sizes; the wheel is the larger of the two circular objects

• large force applied to axle, greater distance of wheel

• small force applied to wheel, large torque on wheel

RADIUS OF WHEEL OR AXLE IS MECH ADVANTAGE

Pulley

A simple machine that consists of a rope that fits into a groove in a FREE SPINNING wheel

• Fixed pulley: changes direction of force but no mech advantage

• Single movable pulley: effort is halved, distance increase by factor of two

• Block and Tackle: multiple pulleys, effort is reduced but amount of rope is increased

# OF PULLEYS AND ROPE LENGTH IS MECH ADVANTAGE

Screw

a simple machine that consists of an inclined plane wrapped around a cylinder

• converts rotary motion to linear motion

• large output forces

Pitch: linear distance traveled in one revolution, small pitch is greater force

Types of Mechanical Motion:

• Linear: straight line (box up a ramp)

• Reciprocating: back and forth (saw)

• Rotary: continuous circular (fan)

• Oscillating: back and forth along an arc on a pivot (pendulum)

• Intermittent: starts and stops predictably (clock)

• Irregular: no pattern (robot)

Mechanism

A system of mechanical parts connected to a drive source

• Transfer between types of motion

• to classify as mechanism, must have a predictable output motion based on known input motion

Gear

A circular toothed object used to transfer rotary motion and torque from one shaft to another

Torque

rotational force

Gear Train

• 2 or more gears in mesh

• only one gear per shaft

• small gear to big: more force

• big gear to small: more speed

• changes or maintains rotational direction

In order to Mesh...

Pressure Angle: Angle of the gear tooth itself

Gear Pitch: Number of gear teeth per arc length

Pitch Circle: Where the gear teeth meet the circumference of the wheel;

all must be equal to the second gear in mesh

Pinion

smaller of two gears

Compound gear train

two gears of different sizes are locked to the same idler gear shaft. Have a greater ability to increase/decrease rotational speed and torque.

Drive gear

the input gear

Driven gear

the output gear

Idler

bridges the gap between input and output gear, may be used to change rotational direction

Gear ratio

# teeth in driving gear (front)/# teeth in driven gear (rear)

Spur gear

• straight cut teeth, uses parallel shafts

Pros: low cost, easy to build, high precision

Cons: limited distance, not good at high speeds or stress