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Palancas, levers

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- 1. DEPARTAMEN OF TECHNOLOGY. 074127GT196 070210 Levers ENRIQUE HEREDIA FERNÁNDEZ
- 2. LEVERS
- 3. Key Questions: <ul><ul><ul><li>1 Analyze and label the parts of a lever and evaluate how a lever multiplies force. </li></ul></ul></ul><ul><ul><ul><li>2 Provide examples of first, second and third class levers. </li></ul></ul></ul><ul><ul><ul><li>3 Compare parts of the human body to the types of levers. </li></ul></ul></ul><ul><ul><ul><li>4 Calculate and determine the mechanical advantage of a lever. </li></ul></ul></ul>
- 4. Forces in Machines <ul><li>A simple machine is an unpowered mechanical device, such as a lever . </li></ul>Pulleys
- 5. Introducing… The Lever <ul><li>A lever includes a stiff structure (the lever) that rotates around a fixed point called the fulcrum . </li></ul>fulcrum
- 6. Anatomy of the lever <ul><li>Fulcrum – point around which the lever rotates </li></ul><ul><li>Input Force – Force exerted ON the lever </li></ul><ul><li>Output Force – Force exerted BY the lever </li></ul>
- 7. Levers and the human body <ul><li>Your body contains muscles attached to bones in ways that act as levers. </li></ul><ul><li>Here the biceps muscle attached in front of the elbow opposes the muscles in the forearm. </li></ul>Can you think of other muscle levers in your body?
- 8. Three Classes of Levers <ul><li>First Class - fulcrum between Input and output </li></ul><ul><li>Second Class – output between fulcrum and input </li></ul><ul><li>Third Class – input between fulcrum and output </li></ul>
- 10. Lever – First Class <ul><li>Here we have a first class lever </li></ul><ul><li>The fulcrum is between the input and output </li></ul><ul><li>Can you get two weights to balance? </li></ul>
- 11. Levers in Equilibrium <ul><li>Hang your weights like shown here </li></ul><ul><li>Does the lever balance? </li></ul><ul><li>What variables can be changed to balance a lever? </li></ul>3 2 1 0 1 2 3
- 12. Four Variables in a Lever <ul><li>Amount of Input Force F </li></ul><ul><li>Amount of Output Force R </li></ul><ul><li>Length of Input Arm L 1 </li></ul><ul><li>Length of Output Arm L 2 </li></ul>
- 13. Lever Challenge <ul><li>Hang weights from the lever and get it to balance. </li></ul><ul><li>Use at least 3 strings! </li></ul><ul><li>Do 4 trials and record how many weights to hang and where you hang them. </li></ul>
- 14. Lever Challenge
- 15. Lever Modification <ul><li>Hang 1 weight 10 cm from the fulcrum. </li></ul><ul><li>Where does the output force need to be to oppose our input force? </li></ul>1 1
- 16. Basic Lever Investigation <ul><li>If we move the input force 10 cm, how much more do we need to add for the same output force? </li></ul><ul><li>Try it... </li></ul>1
- 17. Basic Lever Investigation <ul><li>If we move the input force 10 more cm, how much more do we need to add for the same output force? </li></ul><ul><li>Add two masses at 20 cm. </li></ul><ul><li>HINT: you will need two strings </li></ul>1
- 18. Mathematical Rule for Balancing the Lever <ul><li>What mathematical relationship can you find that will balance the lever every time? </li></ul><ul><li>Put your rule in terms of input and output and forces and distances. </li></ul><ul><li>What if there is more than one location on either side of the lever? </li></ul>
- 19. What is the Relationship? <ul><li>Force x Distance = Force x Distance </li></ul>Input Force x Length of Input Arm # of Weights x Distance Output Force x Length of Output Arm = # of Weights x Distance =
- 20. What if there several groups of weights ? <ul><li>Sum of Input = Sum of Output </li></ul>(F 1 x D 1 ) + (F 2 x D 2 ) (F 3 x D 3 ) + (F 4 x D 4 ) =
- 21. <ul><li>T </li></ul><ul><li>END </li></ul>

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