1. 1 Work and Simple Machines

2. 2 What is work?  In science, the word work has a different meaning than you may be familiar with.  The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

3. 3 To do work: A force must be applied to an object The object must move in the direction of the force If the object does not move….NO work is done….no matter how much force is applied!

4. 4 Formula for work Work = Force x Distance  The unit of force is newtons  The unit of distance is meters  The unit of work is newton-meters  One newton-meter is equal to one joule  So, the unit of work is a joule

5. 5 Power  Power is the rate at which work is done.  Power = Work * /Time * (force x distance) * (force x distance)  The unit of power is the watt.

6. 6 Power Amount of work you do on an object is not affected by how long it takes you to do the work Example: If you carry a backpack up a flight of stairs, the work you do is the weight of the backpack times the height of the stairs. Another example: A car that can accelerate from 0 km/hr to 50 km/hr in 10 seconds has more power than one that accelerates from 0 km/hr to 50 km/hr in 20 seconds.

7. 7 Simple Machines do the following: transferring a force from one place to another, transferring a force from one place to another, changing the direction of a force, changing the direction of a force, increasing the magnitude of a force, or increasing the magnitude of a force, or increasing the distance or speed of a force. increasing the distance or speed of a force.

8. 8 Mechanical Advantage  It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task).  When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.

9. 9 Wheel and Axle  The wheel and axle is a simple machine consisting of a large wheel rigidly secured to a smaller wheel or shaft, called an axle.  When either the wheel or axle turns, the other part also turns. One full revolution of either part causes one full revolution of the other part.

10. 10 Wheel and Axle  Examples of Wheel and Axle: Door Knob, Screw Driver, Pencil Sharpener Handle

11. 11 Pulley  A pulley consists of a grooved wheel that turns freely in a frame called a block.  A pulley can be used to simply change the direction of a force or to gain a mechanical advantage, depending on how the pulley is arranged.  A pulley is said to be a fixed pulley if it does not rise or fall with the load being moved. A fixed pulley changes the direction of a force;

12. 12 Examples of pulleys

13. 13 Screw  The screw is also a modified version of the inclined plane.  While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).

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16. 16 Efficiency  We said that the input force times the distance equals the output force times distance, or: Input Force x Distance = Output Force x Distance However, some output force is lost due to friction.  The comparison of work input to work output is called efficiency.  No machine has 100 percent efficiency due to friction.