Compound Machines

Compound Machines is a 2014-2015 event for Division C in which students answer questions on simple and compound machines, and use a compound lever to determine the ratios of 3 unknown masses. Students should bring their device and any other supplies for impound, a binder of notes, and any calculator.

Compound Machines can be considered the Division C equivalent of the Division B event, Simple Machines.

General Overview

Compound Machines is an event in which you take a written test over compound and simple machines, and create and use a device to accurately and quickly determine the ratios of some unknown masses.

This event covers all 6 simple machines: lever, pulley, inclined plane, wedge, screw, and wheel and axle. The event will mainly test knowledge of these simple machines used together, which are known as compound machines.

Simple and compound machines are tools that help change the direction and magnitude of the force and the distance that the force is applied over--this can makes the work "easier" to do.

Written Test

The written test for Compound Machines tests knowledge over the different types of simple and compound machines and making calculations about the forces involved in these machines at static equilibrium. This test can include topics such as simple and compound machine terminology, mechanical advantage, load, effort, energy, and friction. Free response answers must include metric units and significant figures. For this section of the test, you are allowed one binder of reference materials. This will not need to be impounded.

Terms

The Simple Machines page has in depth information on these devices if further reference is needed.

Machine: A mechanical device that improves or assists in labor using force inputted, and converts it do a different type of force or direction

Simple Machine: There are 6 Simple Machines. These are all different types of machines that change the input force to a different output. They are:

1) Lever

2) Inclined plane

3) Wedge

4) Pulley

5) Wheels and axle

6) Screw

Compound Machine: A machine made up of more than one simple machine. A compound Machine can allow more complex machines and more complex outputs and functions. For example, a scissor combines three different simple machines. 1) Lever: handle, 2) Wheel and Axle: the pin to attach both sides, 3) Wedge: blades

Ideal Mechanical Advantage (IMA): The mechanical advantage under ideal conditions, when no friction or air resistance is present. The IMA has different equations depending on the machine. The most simple and generic way to calculate it is dividing distance in by distance out.

Actual Mechanical Advantage (AMA): The mechanical advantage under real conditions, i.e. when friction and air resistance are present. It is always lower than the IMA due to energy losses associated with non-ideal conditions. AMA can always be calculated by dividing output force by input force.

Efficiency: A measure of how ideal a machine is. Efficiency is usually denoted by η, the Greek letter Eta, and is equal to the output work divided by the input work, which in turn is equal to the AMA divided by the IMA.

The Device

The device test for Compound Machines involves making a series of levers that will be able to determine the mass ratios of 3 weights as quickly and accurately as possible.

Construction Restrictions

The device must be made of a Class 1 and Class 2 lever connected in series. The length of each lever should be less than 40cm. This device can be made out of anything except anything electronic and must not include springs. You are not allowed to bring any masses of your own with you into the competition to determine the weights of the unknown masses.

The Device in the Competition

The supervisors will give your team 3 masses, labeled A, B, and C. You have a maximum of 4 minutes to determine the mass ratios A/B and B/C using your compound machine. This must be done as accurately and quickly as possible.

For the scoring of the device there are two factors, first is time. The time score is calculated as: Points = [math]\displaystyle{ ((240 - Elapsed\,Time\,in\,Seconds)/(240))*10 }[/math]

The second and more important factor is the accuracy. The score for accuracy is calculated as: Points = [math]\displaystyle{ (1-(abs(Actual\,Ratio - Calculated\,Ratio)/Actual\,Ratio))*20 }[/math]

Types of Machines

All concept questions will be limited to the topics of levers, inclined planes, wedges, pulleys, wheels and axles, and screws. See the Simple Machines page for more in-depth information.

Other machines that one may see include gears and Belt and pulley systems.