Simple Machines SPS8. Students will determine relationships among force, mass, and motion. e. Calculate amounts of work and mechanical advantage using simple machines.  

Key Ideas Machines make work easier. Six types of simple machines make work easier. Machines can change the size, distance or direction of a force. Simple machines can be combined to make complex machines.

Review Work happens when a force moves an object W = F x d Work is measured in Joules (Newtons x meters) Power is the rate at which work is done Power = Work / time Power is measured in Watts (joules/second)

Machines Make Work Easier Remember that “Work” is what happens when a force is used to move (displace) an object. Machines do not reduce the amount of work done. Machines can be powered by different kinds of energy. Machines can change either: Direction of the force Distance the force is applied Size of the Force

Machines Can Change the Size of the Force The work you put in is equal to the work you get out. But you can change the size of the force to make work easier. How? Work = Force x Distance If the Work is the same, and the Distance is increased, what happens to the Force that is required to do the Work? Force and Distance are INVERSELY proportional!

Machines Can Change the Distance of the Force Remember: Work = Force x Distance The same formula also means that when Machines change the SIZE of a force, the DISTANCE must change inversely. If the amount of force is reduced, the distance will be increased. If the distance is reduced, the amount of force required will be greater. What happens to the distance as the angle increases? What happens to the force needed to move an object to the top of the ramp?

Machines Can Change the Direction of a Force Some machines change the direction of a force: Push shovel down, dirt goes up Push down on car jack, car goes up Swing ax downward, word splits apart. There is no force or distance tradeoff, but sometimes it is easier to apply a force in a different direction.

Input & Output Forces Two forces involved when machines are used to do work: Input – force applied TO machine (Fin) Output – force applied BY machine (Fout) Work put INTO a machine should be greater than the work DONE by the machine

Six Types of Simple Machines A “Simple Machine” is one which does work with only one movement of the machine. All other machines are either modifications or combinations of these. These are divided into two families: 1- Levers & 2 - Inclined Planes

SIZE (FORCE), DISTANCE &/or DIRECTION Trade offs: SIZE (FORCE), DISTANCE &/or DIRECTION Levers A lever is a bar that turns around a fixed point, called the fulcrum. The effort or input arm is where the force is applied The resistance arm is where the load is located. The closer the fulcrum to the load, the less force needed to lift the load. The closer the fulcrum to the force, the greater the force needed to lift the load. There are three classes of levers, depending on the position of each:

SIZE (FORCE), DISTANCE, and/or DIRECTION Trade Offs: SIZE (FORCE), DISTANCE, and/or DIRECTION Wheel & Axle A wheel and axle is a lever that rotates in a circle around a center point (axle) which is the fulcrum. A wheel is a lever that can turn 360 degrees and can have an effort or resistance applied anywhere on that surface. Wheels can also have a solid shaft with the center core as the axle such as a screwdriver or drill bit or the log in a log rolling contest. Gears are wheels with teeth that can be used to gain force or speed or change direction.

SIZE(FORCE), DISTANCE and/or DIRECTION Trade Offs: SIZE(FORCE), DISTANCE and/or DIRECTION Pulleys A pulley is a wheel with a grooved rim and a rope or cable that rides in the groove. A fixed pulley is fastened to one spot, and does not move around. It provides no gain in force, distance or speed, but it changes the direction of the force. A fixed pulley acts as a first class lever. A single pulley just changes the direction of the force. Multiple pulley systems change the direction and distance of the force. Multiple pulleys can be combined into a single unit called a “block & tackle.”

Inclined Planes Trade Offs: Less SIZE (FORCE) for Increased DISTANCE An inclined plane is a slanted surface used to raise an object. When an object is moved up an inclined plane, less effort is needed than if you were to lift it straight up, but, you must move the object over a greater distance. They make work easier because they support part of the weight of the object while it is being moved.

Trade Offs: Direction is Changed Wedge A wedge is an inclined plane which moves. Most wedges (but not all) are combinations of two inclined planes. Generally it can be anything that splits, cuts, or divides another object including air and water. The angle of the cutting edge determines how easy it can cut through an object.

Less SIZE (FORCE) for Greater DISTANCE Trade Offs: Less SIZE (FORCE) for Greater DISTANCE Screw A screw, like a wedge, is another form of an inclined plane. A screw is an inclined plane wrapped around a cylinder to form a spiral. The advantage of using a screw is the large amount of friction that keeps it from turning and becoming loose.

Mechanical Advantage The benefit of doing work with a machine means less force is needed to do work The number of times a machine multiples the input force is called the machine’s MECHANICAL ADVANTAGE Machines that allow less force over greater distance (ramp) have a MA of greater than 1 Machines that allow more force over shorter distance (rake) have a MA of less than one Machines that change the direction of the force (crowbar), but not the amount, have a MA of one Ideal Situation: No Friction!

Compound Machines Compound machines are two or more simple machines working together. A wheelbarrow is an example of a complex machine that uses a lever and a wheel and axle. A Rube-Goldberg device is an invention that uses simple machines to make complex devices that perform simple tasks in indirect, convoluted ways. Videos: http://www.youtube.com/watch?v=qybUFnY7Y8w http://www.youtube.com/watch?v=lCYg_gz4fDo

Online Resources: Simple Machines: http://www.cosi.org/files/Flash/simpMach/sm1.swf http://42explore.com/smplmac.htm http://www.tooter4kids.com/Simple_Machines/ http://teacher.scholastic.com/dirtrep/simple/index.htm http://www.mos.org/sln/Leonardo/LeosMysteriousMachinery.html http://www.harcourtschool.com/activity/machines/simple_machines.htm http://www.mos.org/sln/Leonardo/GadgetAnatomy.html YouTube Videos: http://www.youtube.com/watch?v=oWiZ_5qvs7I http://www.youtube.com/watch?v=TlPWy7qW7oM&feature=related

Activities & Assignments Simple Machine Flipbook Designa Rube Goldberg Machine Gizmo – Levers