Complex machines are most often a set of simple applications of simple machines, organized and sequenced to complete a job which has multiple tasks. An example of this is a seed drill for planting wheat. Each row is seeded after a wedge attached to the end of a lever has opened the soil, the seed has been inserted, and the soil closed by a wheel and axle. A number of these components ganged together produces the bulk of the operating system. The control of the seed flow, depth that the soil openers run, and a host of other variables are controlled by other applications of pulleys, levers, and other simple machines.
This unit gives students a chance to review the principles of the simple machines, analyze the construction of complex machines, and design some machines of their own.
Science writing and reading activities, as discussed in this Guide, should be incorporated into each lesson. Writing in personal, reflective journals, reading from newspapers, and reporting on the activities of science class in a variety of ways are only three strategies through which students may refine their understanding of the concepts of science and develop their ability to communicate through the written word. Examples of activities which contain a writing or reading components are found in the Suggested activities section of this unit.
Science challenge, as described in this Guide, is meant to extend students' critical and creative thinking abilities in the context of the science concepts being studied. Activities involving science challenge should be incorporated into science lessons in each unit. The challenge is intended to give each student a chance to investigate an area of interest in more depth than would be possible for all students in a class to do. Science challenge is a key strategy for bringing the Adaptive Dimension to the classroom, and for encouraging independent learning. The extension phase of each lesson is an ideal place for students to create their own challenge opportunities or to choose from opportunities suggested to them.
In small groups, brainstorm to produce a list of such mechanical devices which could be used around home or at school. Select several and produce sketches of such machines. Can you identify any machines that actually exist that come close to falling in the category of Rube Goldberg machines?
Factors: A9, B6, B10, C4, C14, D2, E3, F5, G1
Objectives: 2.1, 2.2, 2.3
Assessment Techniques: peer assessment, rating scale, presentations
Instructional Method: problem solving
Can you think of any product that two or three years ago you had never
heard of, but now is considered something you need. Ask your parents or
grandparents if they can think of any devices that fit in this category.
Assessment Techniques: self and peer evaluations, rating scales,
presentations, oral assessment
Instructional Methods: cooperative group learning, model building,
problem solving
Physicists calculate the amount of work done by multiplying the force
applied by the distance in metres over which the force is exerted. Force
is measured in units of newtons. 1 newton (1 N) of force is the
amount of force required to lift a mass of 100 grams. 1 newton exerted over
a distance of 1 metre is called 1 joule (1 J) of work. To calculate work
done you must be able to measure both the force applied and the distance
over which the force was applied.
Gravity exerts a force on all objects. The downwards force on a mass of
100 grams at the surface of the earth is 1 newton. This downwards force
is called weight. How much downwards force is there on a mass of 500 grams?
On a mass of 4.5 kg? On your mass? If you were to be transported to
the moon, your mass would stay about the same, but your weight would be
a lot less. Why would this be?
Make a device that can measure the amount of force applied to an object.
Standard masses for calibrating your instrument can be made by adding sand
to empty 35 mm film canisters or baby food jars. If these standard
masses are produced in fractions or multiples of 100 grams, then the
forces to lift them will be in fractions or multiples of 1 N.
Use your device to measure force inputs and outputs of various simple
machines and household items. How much force does it take to depress the
arm of a equal-arm first class lever (like a teeter-totter) loaded with
a 500 gram mass? To raise a 100 gram mass with a pulley? To pull down
a window blind? To turn on a light switch? To open a drawer?