*When you use a machine to do work, there is always an exchange, or tradeoff, between the force you use and the distance over which you apply that force. You can use less force over a greater distance or a greater force over a shorter dista n ce to do the same amount of work. Machine-Any device that makes doing work easier. Mechanical Advantage-The number of times a machine multiplies the input force; output force divided by input force. Efficiency-The percentage of the input work done on a machine that the machine can return in output work; a machine’s output work divided by its input work and multiplied by 100.

*I. Machines help people do work. A.Machines change the way force is applied Technology is using knowledge to create tools that make life easier! Machines change the way work is done… doesn’t decrease the work! Machines change the size of the force and distance over which it is applied and the direction in which The force is exerted!

1.*Changing the Size and Distance of a Force a. Allows you to exert less force and greater distance (opening a door with a door knob) b. Allows you to apply a greater input force over a shorter distance (ex. Raking leaves) c. Input force is a force exerted on a machine d. Output force is force machine exerts on an object 2. Changing the Direction of a Force a. Pulling a rope to raise the flag on a flagpole b. Shovel to dig a hole See page 451

*3. Mechanical Advantage of a Machine Mechanical advantage= output force input force B. Work transfers energy. 1.Energy a.lifting an object- gravitation PE b. See example p Work See page for climbing example

*C. Output work is always less than input work. Efficiency= output work x 100 input work 1.Efficiency and Energy ***if more mechanical energy is lost in the transfer to other forms of energy, then the machine is less efficient ***Some machines lose energy in the form of heat (friction)- more parts, more rubbing together, more loss See examples p. 455

82. Increasing Efficiency Reduce friction (example: oil or grease) See example p. 456

Practice Problems The output force of a machine is 600N, and the input force is 200N. What is the mechanical advantage of the machine. A machine has an input force of 150N and a mechanical advantage of 0.5. What is the output force? The output force of a machine is 135N, and the mechanical advantage is 2.5. What is the input force? If someone does 500J of work on a pair of pliers and the pliers do 300J of work on a wire, what is the efficiency of the pliers?

More Practice A construction worker does 1000J of work in pulling down on a rope to lift a weight tied to the other end. If the output work is of the rope system is 550J, what is the ratio of output work to input work? What is the efficiency of the rope system? If a machine takes 20,000J and puts out 5000J, what is its efficiency? You do 6000J of work to pull a sled up a ramp. After you reach the top, you discover that the sled had 3600J of work done on it. What is the efficiency of the ramp? If you put 7000J of work into a machine with an efficiency of 50%, how much work will you get out? What is the mechanical advantage if the output force is 60N and the input force is 15N?

*Simple machines change the size and/or direction of a force. II. Six simple machines have many uses. A.There are six simple machines. All mechanical machines are based on these six. 1.Lever a. Solid bar rotates around a fixed point (fulcrum). b. Multiplies or changes the direction of the input force c. See diagram p. 459

*2. Wheel and Axle a. A wheel attached to a shaft (axle)- rotating collection of levers b. Input force is transferred to axle when you turn a wheel and vice versa 3. Pulley a. Wheel with a grooved wheel and a rope or cable that rides in the groove b. As you pull the rope, the wheel turns. C. A fixed pulley changes the direction of the force; movable pulley-one end of rope is fixed and the wheel can move d. Allows you to use the downward pull of your weight

4. Inclined Plane a. A sloping surface (ramp) b. Help support part of the weight of the object c. The less steep, the less force needed, greater distance *e. Combination of fixed and movable pulley is called block and tackle-used to lift and haul heavy objects. 5. Wedge a. Has thick end and thin end b. Used to cut, split, or pierce objects/or hold objects together c. An inclined plane that moves! d. See example p. 462 e. Thin wedges, small angles, less force; thick wedges, greater force, larger angles ***smaller surface-greater PRESSURE! P.463

*6. Screw a. Inclined plane wrapped around a cylinder or cone to form a spiral b. Used to raise and lower weights or fasten objects c. Provides larger amounts of friction d. See page 463 B. The mechanical advantage of a machine can be calculated. MA=F out F in See page for calculations for different Machines!

Calculate What is the ideal mechanical advantage of a wheel with a diameter of 30cm fixed to an axle with a diameter of 4cm if the axle is turned? A gear with 15 teeth turns another gear with 20 teeth. What is the mechanical advantage of the gear system?

III. Modern technology uses compound machines. How does a tow truck do work? A.Compound machines are combinations of simple machines. Examples: Scissors- a combination of 2 levers with cutting edges shaped like a wedge Fishing rod- lever with fishing line wound around a wheel and axle 1.Gears a. Based on wheel and axle and have teeth so gears can turn one another b. If sized exactly and identical, they have the same speed in opposite directions. c. A third gear is necessary for two others to turn in the same direction

2. Mechanical Advantage of Compound Machines a. Equal to the product of the mechanical advantages of all the simple machines that make up the compound machine. b. Compound machines must overcome more friction than simple machines B. Modern technology creates new uses for machines. Examples: Jaws of Life tool that helps rescue people involved in accidents ***Powered by hydraulics to help pry open metal vehicles or collapsed concrete structures ***Two levers and two wedges (Photo p. 470) Name one other example used for human arteries!

1.Microtechnology and Nanotechnology a. too small to be seen by the naked eye; visible under a microscope b. What inspired scientists to develop nano-machines? c. How small are these? d. built from the bottom-up e. Still in the experimental stage Read page and list examples of this new form of technology. 2. Robots a. works automatically or with a remote control b. Most DO NOT resemble humans!-Built to do things humans can’t ! c. Example: Pyramid Rover p.472 d. Companies use robots to manufacture goods quickly and efficiently (welding, painting, assembling products/ automobile and computer industries).