Bell Ringer  Why do we use machines?  What is the formula for work?  What are the SI units for work?  What is the formula for power?  What are the SI units for power?

Simple Machines

 Simple machines do work with only one movement.  A machine made of a combination of simple machines and makes more than one movement is a compound machine.

1. Inclined plane  A flat, sloped surface.  Less force is needed to move an object from one height to another using an inclined plane than is needed to lift the object.  The mechanical advantage of an incline is the length of the inclined plane divided by its height.  Ex: Ramp

2. Wedge  An inclined plane that moves  It changes the direction of the applied force.  A wedge is really an inclined plane turned on its side. But instead of helping you move things to a higher level, a wedge helps you push things apart.  Ex: blades of a knife, axe, door stop, or a shovel  MA = length width width

 A wedge can also be round, like the tip of a nail, or the tines on your fork.  Basically, the wedge works just like a ramp: The narrower the wedge (or the sharper the point of a wedge), the easier it is drive it in and push things apart.  But here's the trade-off: To split something apart really wide, you have to push the wedge a long distance.  We can use the wedge action to cut and shape ice and wood sculptures.

3. Screw  An inclined plane wrapped around a cylinder or post.  The inclined plane forms the screw threads (spiral) on a screw.  A screw is a simple machine that is made from another simple machine. It is actually an inclined plane that winds around itself.  A screw is a simple machine that is made from another simple machine. It is actually an inclined plane that winds around itself.

 A screw has ridges and is not smooth like a nail. Some screws are used to lower and raise things. They are also used to hold objects together.  Ex: screws, jar lids  The mechanical advantage of the screw is the length of the inclined plane wrapped around the screw divided by the length of the screw.

Video   Inclined Plane, Screw, Wedge Inclined Plane, Screw, Wedge   Quiz After!!

Bell Ringer Solve the following problems. Include units and show your work!!  A force of 15 newtons is used to push a box along the floor a distance of 3 meters. How much work is done?  A book that weighs 1 N is lifted 2 meters. How much work is done?  It took 50 joules to push a chair 5 meters across the floor. With what force was the chair pushed?

4. Lever  Any rigid rod or plank that pivots about a point.  The point about which the lever pivots is called a fulcrum.  Levers can be divided into 3 classes depending on the position of the fulcrum.  The mechanical advantage is dividing the distance from the fulcrum to the input force by the distance from the fulcrum to the output force.

5. Wheel and Axle  Two circular objects of different sizes that rotate together.  A wheel and axle is a lever that rotates in a circle around a center point or fulcrum.  The larger wheel (or outside) rotates around the smaller wheel (axle).

 Bicycle wheels, ferris wheels and gears are all examples of a wheel and axle.  Wheels can also have a solid shaft with the center core as the axle such as a screwdriver or drill bit or the log in a log rolling contest.

6. Pulley  The pulley is a simple machine made of a wheel with a rope or belt wrapped around it. It is used to lift things up.  The pulley is a simple machine made of a wheel with a rope or belt wrapped around it. It is used to lift things up.  When you pull down on one end of the rope, the other end moves upward. A pulley can help move an object to a place that is hard to reach..  Fixed pulleys such as on window blinds or flagpoles, are attached to an overhead structure and change the direction of the force you exert.

Exit Quiz  What is the name for a flat, sloped, surface?  What is the simple machine that is involved in a flagpole?  Tell me an example of a lever in the real world.  Why do we use machines?