Simple Machines and Mechanical Advantage

Simple Machines

Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

Simple Machines

• The six simple machines are:– Lever – Wheel and Axle – Pulley – Inclined Plane – Wedge – Screw

Simple Machines

• A machine is a device that helps make work easier to perform by accomplishing one or more of the following functions: – transferring a force from one place to

another, – changing the direction of a force, – increasing the magnitude of a force, or – increasing the distance or speed of a

force.

Mechanical Advantage

• It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task).

• When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.

Mechanical Advantage

• Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one.

• If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10.

• In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance.

MA = output/input

VERY IMPORTANT !

No machine can increase both the magnitude and the distance of a force at the same time.

The 6 Simple Machines

Lever

Pulley Wheel and Axle

WedgeScrewInclined Plane

Inclined Plane

Inclined Plane• The Egyptians used simple machines to build the

pyramids. One method was to build a very long incline out of dirt that rose upward to the top of the pyramid very gently. The blocks of stone were placed on large logs (another type of simple machine - the wheel and axle) and pushed slowly up the long, gentle inclined plane to the top of the pyramid.

Inclined Planes• An inclined plane is a

flat surface that is higher on one end

• Inclined planes make the work of moving things easier

The Lever

• A lever is a rigid bar that rotates around a fixed point called the fulcrum.

• The bar may be either straight or curved.

• In use, a lever has both an effort (or applied) force and a load (resistant force).

There are 3 Classes of Levers

• Depends on the location of 3 items:1. Fulcrum – fixed point

on a lever 2. Effort Arm – the part

of the lever that exerts the effort force.3. Resistance Arm – the

part of the lever that exerts the resistance force.

EA

RA

1st Class Lever

– Changes the direction of the force

– Multiplies effort force– Magnifies speed and

distance– Ex: seesaw, crowbar,

scissors

2nd Class Lever

– Multiply effort force– Mechanical advantage

is always greater than 1.

– Ex: bottle opener, boat oars, wheel barrow

3rd Class Lever

– Magnifies speed and distance

– Mechanical Advantage always less than 1

– Ex: baseball bat, golf club, broom, shovel

WHEEL AND AXEL• The axle is stuck

rigidly to a large wheel. Fan blades are attached to the wheel. When the axel turns, the fan blades spin.

Pulleys• Pulley are wheels and

axles with a groove around the outside

• A pulley needs a rope, chain or belt around the groove to make it do work

Diagrams of Pulleys

Fixed pulley: A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage.

Movable Pulley: The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

COMBINED PULLEY• The effort needed to

lift the load is less than half the weight of the load.

• The main disadvantage is it travels a very long distance. 

Mechanical Advantage

• Ratio of Output Force to Input Force

• Follows simple pattern with Ropes and Pulley system

Rube Goldberg Machines• Rube Goldberg machines are

examples of complex machines.• All complex machines are made

up of combinations of simple machines.

• Rube Goldberg machines are usually a complicated combination of simple machines.

• By studying the components of Rube Goldberg machines, we learn more about simple machines