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Simple Machines

This lesson covers the basics of wheel and axle, as well as the concept and applications of wedges. It includes examples, mechanical advantages, advantages/disadvantages, and a practice quiz. Suitable for simple machines learning.

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Simple Machines

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  1. Simple Machines Practice #5—Wedges Mr. Burleson geaux15@hotmail.com

  2. Agenda • Review • What are Wedges • IMA for different types of Wedges • Simple Machines Practical • Homework

  3. Basics of Simple Machines • Lever • Inclined Plane • Wheel and Axle • Wedge • Pulley • Screw (not included in Machines [B])

  4. What is a Wheel and Axle • Wheel and Axle is a simple machine that is generally considered to be a wheel attached to an axle so that these two parts rotate together in which a force is transferred from one to the other. • The IMA is caused by the difference in radius between the wheel and axle • Either the Wheel or Axle may be the driving force

  5. Wheel and Axle Mechanical Advantage • The force applied to the edge of the wheel is less than the force applied to edge of the axle. • If you have a wheel and axle, each with their own radii, here is the formula • Notice the torques are equal.

  6. Gears are also a Wheel and Axle type of machine • A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque • Usually the teeth on the one gear of identical shape, and often also with that shape (or just width) on the other gear. • Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine.

  7. What is a Wedge? • A wedge is a triangular shaped tool, a compound and portable inclined plane, and one of the six classical simple machines. • It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. • It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces.

  8. Examples of Wedges • Axe • Blade • Knife/Scaple • Log Splittle • Pushpin/Tack/Nail • Throwing Dart/Arrowhead • Scissors • Plug and Feather • Doorstops

  9. Wedge Mechanical Advantage • IMA = Length/Width • Or IMA = 1/tanα, where α is the angle of the wedge • Sharp. The more acute, or narrow, the angle of a wedge, the greater the ratio of the length of its slope to its width, and thus the more mechanical advantage it will yield. • Blunt/Wide. However, in an elastic material such as wood, friction may bind a narrow wedge more easily than a wide one. This is why the head of a splitting maul has a much wider angle than that of an axe. • Higher IMA’s require less force, but will take longer to separate the material

  10. Example #1 • A man wants to split wooden logs and he has an axe and a wood splitting wedge. • Both are 10 cm long • The axe is 2 cm thick • The wood splitting wedge is 5 cm thick • The IMA for the axe is: • IMAaxe = length/width = 10 cm / 2 cm = 5 • The IMA for the wood splitting wedge is: • IMAwedge = length/width = 10 cm / 5 cm = 2

  11. In Practice Quiz • Name three types of wedge simple machines that you know of? • What are the advantages to sharper wedges? Disadvantages? • What are the advantages to blunter wedges? Disadvantages? • Does a sharp or blunt wedge have a higher IMA? • What would be some causes of efficiency loss?

  12. Practical • Now practice with your lever device and see if you can get within 99% accuracy of the actual ratios • Do not time until you have achieved 99% accuracy 3 times in a row

  13. Homework #5 Wedges • Print or draw pictures of wedges other than the ones presented in class, print that out to share with the team. • Use the homework generator for all Wheel/Axle and Wedge Levels.

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