Work and Machines  Work is a form of energy. It is the energy that it takes to cause things to move. Sometimes called Mechanical Energy. The Formula for work is E w = Fd or W = Fd where E w = work energy (unit= Joules) F = (net) force applied d = distance object is moved However, In order for work to really be work, force must be applied in the same direction as the movement.

Simple Machines  Simple machines make work easier by reducing the force applied and/or changing the direction of the force.  The forces involved with any machine is called input/output forces –Input force: anything you do to the machine to make it work –Output force: what the machine does for you

Types of Simple Machines  Lever, Pulley, Wheel and Axel, Inclined plane, Screw, and the wedge are the 6 different types of simple machines.  These machines work by manipulating force (F). You supply the input force and the machine supplies the output force. Pulley or

Mechanical Advantage (MA)  Mechanical Advantage is a value that shows how useful the machine is. It shows the ratio of work into the machine compared to work out of the machine.  The larger the mechanical advantage the more work the machine is doing compared to you. It should always be larger than 1.  There are no units for mechanical advantage because they cancel in the calculation.  larger than 1

Output over Input

Calculating Mechanical Advantage Often the output force is the weight of the object being lifted because this is the force you must exert to make it move or the machine must exert. A pulley will reduce that force and also change the direction of the force. Here you see the mechanical advantage of the pulley is 2.

Pulleys or block and tackle exert a pulling force. If you pull on the rope with a 5N force the rope will pull up with a 5N force. Each time you wrap the rope on a pulley, the force is multiplied. The pulley with 4 ropes has an output force of 20N so the MA is MA= F o = 20N = 4 F i 5N MA for pulleys = counting the ropes

Levers  Levers are sticks or a stiff structure that pivots around a point called a fulcrum.  There are three kinds of levers.

Mechanical advantage of levers  Can also be calculated by: Effort (input) fulcrum distance or force = MA Output fulcrum distance or force MA = 5.5 m = m MA = 10 m = 10 1 m

Gears:  Rotating Machines use gears and shafts to conduct rotating motion.  Gears work better than wheels because they have teeth that interlock as they turn to prevent them from slipping as they turn together. Mechanical Advantage of Gears

Inclined Planes  The mechanical advantage of an inclined plane is the ratio of the force to lift the object straight up compared to the force needed to push it up the ramp. Output force Input force

Efficiency and Loss of Input  When most or all of the work input into a machine is transferred to output, it is said to be efficient. In real machines there is always less output than input. Friction and other forces use up some of the work energy.  Efficiency is measured in a ratio of work output to work input. Divide output by input. Convert to a percent by multiplying by 100.

What is the efficiency of this machine? %Efficiency = Work out (100) Work in = 3 J (100) 4 J = 75%