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Integrated Natural Science

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for Detroit Public Schools Levers Kat Woodring

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Key Questions: Analyze and label the parts of a lever and evaluate how a lever multiplies force Provide examples of first, second and third class levers Compare parts of the human body to the types of levers Calculate and determine the mechanical advantage of a lever.

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District Outcomes Qualitatively and quantitatively explain forces and charges in motion. Observe and explain forces as push and pull, acting on an object and exerted by the object. Analyze the operations of machines in terms of force and motion.

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Lever Assembly SAFETY NOTE: WATCH for FALLING weights on bare toes or sandals or table tops! DO not place the fulcrum higher than hole 3 of stand!

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4.1 Forces in Machines A simple machine is an unpowered mechanical device, such as a lever.

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Introducing… The Lever A lever includes a stiff structure (the lever) that rotates around a fixed point called the fulcrum. fulcrum

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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

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Levers and the human body Your body contains muscles attached to bones in ways that act as levers. Here the biceps muscle attached in front of the elbow opposes the muscles in the forearm. Can you think of other muscle levers in your body?

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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

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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?

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Levers in Equilibrium Hang your weights like shown here Does the lever balance? What variables can be changed to balance a lever?

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Four Variables in a Lever Amount of Input Force Amount of Output Force Length of Input Arm Length of Output Arm

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Lever Challenge Hang weights from the lever and get it to balance. Use at least 3 strings! Do 4 trials and record how many weights to hang and where you hang them.

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Lever Challenge

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Lever Modification Hang 1 weight 10 cm from the fulcrum. Where does the output force need to be to oppose our input force? 11

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Basic Lever Investigation If we move the input force 10 cm, how much more do we need to add for the same output force? Try it... 1

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Basic Lever Investigation If we move the input force 10 more cm, how much more do we need to add for the same output force? Add two masses at 20 cm. HINT: you will need two strings 1

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Basic Levers Investigation

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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?

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What is the Relationship? Force x Distance = Force x Distance Input Force x Length of Input Arm # of Weights x Distance Output Force x Length of Output Arm = # of Weights x Distance =

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What if there several groups of weights ? Sum of Input = Sum of Output (F 1 x D 1 ) + (F 2 x D 2 )(F 3 x D 3 ) + (F 4 x D 4 ) =

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Mechanical Advantage We use the same kind of relationship for all simple machines to calculate Mechanical Advantage. Output Force / Input Force

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4.1 Mechanical Advantage MA = F o F i Output force (N) Input force (N) mechanical advantage

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Michigan Content Expectations P4.1c Explain why work has a more precise scientific meaning than the meaning of work in everyday language. P4.1d Calculate the amount of work done on an object that is moved from one position to another. P4.1e Using the formula of work, derive a formula for change in potential energy of an object lifted in a distance h.

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