1. Chapter 8: Simple Machines Ms. Johnson Foundations

2. Objectives  A simple machine is a device that makes work seem easier. When doing work, a simple machine can change the effort needed and/or the direction or distance over which the effort is applied.  Types of simple machines are the lever, pulley, inclined plane, wheel and axle, screw, and wedge. Many common tools are examples of simple machines.  The work put into a machine is always more than the work output of a machine. Loss of work output is due to friction. Friction in the form of heat is produced when parts rub against each other. Lubricants reduce friction.

3. Vocabulary  Work  Force  Machine  Resistance  Effort  Lever  Pulley  Wheel and axle  Inclined plane  Screw  Wedge  Compound machine

4. Work

5.  Weight is moved over a distance, so work is done.  When the box is at the top, weight is held up motionless, so no work is done.

6. Machines and Work  Machine: a device that transfers mechanical energy from one object to another.  They make work easier by multiplying force and changing the distance (or direction) over which a force is applied.  Ex. A pulley changes the direction of a force  Ex. A wrench multiples the force applied when removing a bolt  Resistance: the force a machine has to overcome.  Effort: the force applied by a machine.  Using a machine can reduce the amount of effort needed to overcome a given amount of resistance.

7. Simple Machines  Many complex modern machines are made up of a number of simple machines working together to perform some work.  The lever and the inclined plane are the most basic simple machines.  Most other simple machines are based on either the lever or the inclined plane.

8. Simple Machines: Lever  A lever consists of a rigid bar that can turn around a point called a fulcrum.  Levers make work easier by multiplying applied forces.  Examples: pliers, scissors, crowbars. Resistance Lever Effort Fulcrum

9. Simple Machines: Pulley  Pulley: a modified form of the lever.  The pulley on the left: The direction of force is changed.  On the right: Force is multiplied. Resistance Effort

10. Simple Machines: Wheel and Axle  Wheel and axle: another modified lever.  Consists of a large wheel with a smaller wheel, or axle, in its center.  When one wheel is turned, so is the other.  Common example: steering wheel, doorknob, screwdriver, and wrench.

11. Simple Machines: Inclined Plane  Inclined plane: a flat surface with one end higher than the other.  Examples: a wheelchair ramp, a staircase, a loading ramp.  An inclined plane makes work easier by changing the direction and distance of a force needed to do a job. Resistance Effort

12. Simple Machines  The screw and the wedge are simple machines that are based on the inclined plane.  A screw is an inclined plane wrapped around a pole.  A wedge consists of two inclined planes placed back to back.  Other examples: knives, nails, teeth on saw blades.

13. Simple Machines

14. Compound Machines  Most machines in daily life are compound machines.  Compound machines: machines made up of more than one simple machine.  Example: Scissors Center ScrewScrew Blade edgeWedge Handle and BladeLever

15. Compound Machines  Example: Bicycle Brake HandlesLever WheelsWheel and Axle ChainPulley Tire BoltsScrew

16. Efficiency of Machines  In a perfect world, a machine’s work output should equal the amount of work put into the machine.  In reality, machines are never 100 percent efficient.  The amount of work done by any machine is always less than the amount of work put into it.  This is because some of the energy gets converted into wasted heat energy.  The heat energy is produced by friction between the machine’s moving parts.

17. Efficiency of Machines  A machine can be more efficient if friction is reduced.  A common way to reduce friction is using lubricant made from grease or oil on the contact surfaces.  You can also wax surfaces or sand surfaces to make them smoother.  A third option is ball bearings.

18. Questions? Chapter 8: Simple Machines