Key Questions How does a lever work? What is the relationship between force and distance in a simple machine? What factors balance a lever?
Overview Describe how a lever works Identify the relationship between force & distance on a lever Apply the concept of mechanical advantage to levers
Introducing… The Lever Anatomy of the lever Fulcrum – point around which the lever rotates Input Force – Force exerted ON the lever Output Force – Force exerted BY the lever
Three Classes of Levers First Class - fulcrum between Input and output Second Class – output between fulcrum and input Third Class – input between fulcrum and output
CPO Lever – First Class All The Way Here we have a first class lever The fulcrum is between the input and output Can you get two weights to balance?
A Lever in Equilibrium Hang your weights like shown here Does the lever balance? What variables can be changed to balance a lever
Variables Involved in Levers Amount of Input Force Amount of Output Force Length of Input Arm Length of Output Arm
Levers Investigation Hang weights from the lever and get it to balance Try 4 trials and record how many weights to hang and where you hang them
Mathematical Rule for Balancing the Lever What mathematical relationship can you find that will balance the lever every time? Put your rule in terms of Input and Output and forces and distances What if there is more than one location on either side of the Lever?
What is the Relationship? Input Force x Length of Input Arm= Output Force x Length of Output arm Force x Distance = Force x Distance # of Weights x Distance = # of Weights x Distance
What if there are several groups of weights? Sum of Input = Sum of Output (Force a x Distance a) + (Force b x Distance b) = (Force c x Distance c) + (Force d x Distance d)
Mechanical Advantage We use the same kind of relationship for all simple machines to calculate Mechanical Advantage Output Force/Input Force Length Input Arm/Length Output Arm