47 Outcome 2: Simple Machines
Outcome/Competency: You will be able to solve physical problems using knowledge of simple machines
Rationale:
Why is it important for you to learn this skill?
Two thousand years ago, an old Greek man once said, “If you give me a lever and a place to stand, I can move the world.” Archimedes realized he could move very heavy object with a long stick, fulcrum, and comparatively little effort. Another simple machine that you will use often is a pulley because it will allow you to lift heavy loads with less effort. With a knowledge of simple machines, you will be able to predict how much effort you need to put into lifting very heavy objects.
Objectives:
To be competent in this area, the individual must be able to:
- Apply calculations and terms used in the study of mechanical work, power and energy
Learning Goals
- Calculate the mechanical advantage, velocity ratio and efficiency of a simple machine
- Apply a simple machine in order to solve a trade related problem.
Introduction:
In this module we will learn the concepts of work, power, and energy with respect to moving objects. Later in the course, we will apply these concepts to moving electrons (electricity.) You will complete practice and review activities throughout the module.
Topic 1: The Concept of Simple Machines
Prerequisite Skills:
- Manipulating equations- a review of algebra may be warranted.
Simply put, machines trade of velocity (distance per time) for force. If something takes too much force to do, a machine will allow you to spread the force over a larger distance, so it becomes manageable. This works both ways. Machines can:
- Reduce the force required by increasing the distance you apply the force
- Reduce the distance required by increasing the applied force
For our purposes, a machine takes energy and performs work. A simple machine has a single input force and a single output force. The input force is called effort and the force produced by the machine is called the load.
Remember, work is the product of force and displacement, so the input work is the product of effort and distance moved by the effort. The output work is the product of the load and the distance moved by the load.
Work
Input work (Nm) = Effort (N) X Distance Moved by Effort (m)
Output work (Nm) = load (N) X Distance Moved by Load (m)
Mechanical Advantage
Ideally, the effort you put into a machine is the same as the load you can lift. The ratio of effort to load, ideally, would be 1. This ideal machine would be 100% efficient. In reality, because of friction, slippage, or other factors, the effort put in is larger than the load that can be lifted. Actual mechanical advantage is less than 1, or less than 100%.
Mechanical Advantage (M.A.)
Example 1:
A simple machine moves a load of 2500 N when an effort of 165 N is applied to the machine. What is the mechanical advantage of the machine?
Solution
The actual load is 2500 N. The actual effort is 165 N.
The machine offers a mechanical adva