2. 1 Simple Machines

3. 2 History of Work Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

4. 3 Simple Machines Ancient people invented simple machines that would help them to do the desired work for difficult tasks.

5. 4 Simple Machines  Machines can make work easier by increasing the force that can be applied to the object A bottle opener increases the force you can apply to a bottle cap, causing the cap to bend A bottle opener increases the force you can apply to a bottle cap, causing the cap to bend A car jack enables you to lift a heavy machine A car jack enables you to lift a heavy machine

6. 5  Machines can make work easier by increasing the distance which a force can be applied. A rake and a ramp make work easier A rake and a ramp make work easier

7. 6  Machines can also make work easier by changing the direction of the applied force When you open a window blind by pulling down on the cord, the downward force on the cord is changed to an upward force that opens the blinds. When you open a window blind by pulling down on the cord, the downward force on the cord is changed to an upward force that opens the blinds.

8.  An ax blade changes the direction of the force from vertical to horizontal splitting the wood. 7

9. Effort and Force  Two forces are involved when a machine is used to do work Effort force (F e ) the force applied to the machine Effort force (F e ) the force applied to the machine Resistance force (F r ) the force applied by the machine Resistance force (F r ) the force applied by the machine 8

10. Effort and Force  Pulling out a nail with a hammer.  You apply the effort force on the handle  The resistance force is the force the claw applies to the nail 9

11. 10 Mechanical Advantage  The number of times a machine multiplies the effort force is the mechanical advantage (MA) of the machine  If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10.  In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance.  MA = output/input

12. Efficency  Machines that loose less energy to friction are said to be efficient.  Efficency is a measure of how much of the work put into a machine is changed into useful out put work by the machine  A machine with a high efficency produces less heat from the friction so more of the input work is changed into useful output work 11

13. Work done by machines  When you use a crowbar to pry the lid off a wooden crate, you are trying to move something that resists being moved.  You are working against the friction between the nails in the lid and the crate.  If you use a crowbar to move a rock, you would be working against gravity. 12

14. Conserving energy  Energy is always conserved. Energy cannot be created or destroyed.  A machine can not create energy so…  W out is never greater than W in. 13

15.  The machine does not transfer all of the energy it receives to the object.  When a machine is used, some of the energy transferred changes to heat due to friction.  The energy that changes to heat cannot be used to do work so…  W out is always smaller than W in 14

16. Ideal machine  If there was a perfect machine built in which there was no friction then none of the input work or output work would be converted to heat.  So for an ideal machine  W in =W out 15