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

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

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

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

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.    

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.

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.

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

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

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

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?

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

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.