Chapter 8 Work and Machines Lesson 1: Work Work when something moves because of a force being applied Work = force x distance Label is newton-meter or joule Work formula w f d Lesson 2: Energy Energy ability to do work There are 2 kinds of energy ◦Kinetic energy in motion ◦KE = ½ mv² ◦Potential stored energy ◦PE = mgh gravity = 9.8 m/s² 6 Forms of Energy Chemical energy stored in the bonds btw. atoms Heat energy moving particles in matter Mechanical energy in moving objects 6 Forms of Energy cont. Nuclear energy stored in the nucleus of atoms Radiant energy light energy Electrical energy causes electrons to move Energy can be converted from one form to another Generator device used to convert mechanical energy to electrical energy Law of conservation of energy energy cannot be created nor destroyed Lesson 3: Levers Simple machines tool that makes it easier or possible to do work Lever bar that is free to turn around a fixed point Fulcrum fixed point around a lever turns Levers cont. Effort force (FE force applied to a machine by the user Resistance force (FR) force applied to the machine by the object to be moved 3 Classes of Levers Based on the position of the resistance, fulcrum, & effort First-class lever fulcrum is btw effort & resistance Changes direction of force & can increase force Examples of class 1 levers include: Teeter-totter Scissors Pair of pliers Second-class lever resistance is btw effort and fulcrum Always increases force Do not change direction Examples of class 2 levers include: Wheelbarrow Crowbar Nut cracker Third-class levers effort is btw resistance & fulcrum Increases distance which cause resistance to move further or faster Examples of class 3 levers include: Tweezers Mousetrap Stapler Broom Hockey stick Efficiency A simple machine cannot do more work than the person using it Machines increase or change the direction of force If less effort is needed, more distance is needed also Effort distance & resistance distance Effort distance (dE) the distance the effort moves Resistance distance (dR) the distance the resistance moves Effort distance is greater than resistance distance Work Input & Work Output Work input work put into a machine by the user ◦Work input = FE x dE Work output work done by a machine against the resistance ◦Work output = FR x dR Efficiency Efficiency = work output work input FR x dR FE x dE x 100 x 100 Lesson 4: Mechanical advantage Mechanical advantage number of times a machine multiplies its effort force ◦Mechanical advantage = resistance force effort force ◦MA = FR FE Effort Arm & Resistance Arm Effort arm distance btw the fulcrum & effort force Resistance arm distance btw the fulcrum & resistance force ◦MA = effort arm resistance arm Lesson 5: Other simple machines Pulley wheel w/ a rope, chain, or belt around it A single pulley changes direction, not force; ma = 1 Fixed pulley attached at top Movable pulley entire pulley & object attached will rise Pulley cont. MA of a pulley = number of ropes that pull upward The easier to lift an object, the more distance you pull on the rope Inclined Plane Inclined plane made of a ramp used to lift an object MA = length of ramp height of ramp ◦Gradual slant = greater MA, but greater distance ◦Steeper slant = less MA, but shorter distance Screw Screw inclined plane wrapped around a nail MA depends on distance btw threads ◦Smaller distance = more MA Wedge Wedge 2 inclined planes placed back to back; inclined plane that moves when used Thick at one end, thinner at the other ◦Thinner, more gradual wedge = greater MA Wheel & Axle Wheel & axle wheel attached to a shaft Increases the force you apply to the wheel MA depends on the size of the wheel & thickness of axle