Key Questions: What is a newton? How does a lever work? What is the relationship between force and distance in a simple machine? What factors balance a lever? These are the key questions for our investigation. Key questions challenge students to explore the parts of a lever system and how the lever works. By using the equipment and experimenting, students get a first hand feel for the scientific process as they develop ideas and test their hypothesis.

Performance Objectives Describe how a lever works. Identify the relationship between force and distance on a lever. Apply the concept of mechanical advantage to levers.

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!

FORCES Forces have two important properties: strength (magnitude) and direction. In the English system of units, the strength of a force is measured in pounds. When you measure your own weight in pounds, you are measuring the force of gravity acting on your body.

The NEWTON In the metric system, the strength of a force is measured in newtons (N). A quarter-pound hamburger has a weight of about 1 newton (1 lb = 4.448 N).

Zero the Spring Scale In the metric system, the strength of a force is measured in newtons (N).

Gravity and weight The force of gravity on an object is called weight. Mass and weight are not the same thing!

Gravity and weight A 10-kilogram rock has a mass of 10 kilograms no matter where it is in the universe. A 10-kilogram rock’s weight however, can vary greatly depending on where it is.

Simple Machines A simple machine is an unpowered mechanical device, such as a lever. Simple machines change the magnitude or direction of forces

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

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 The Lever is a simple machine. A simple machine is a device that has an input and output force. The Fulcrum is the point around which the lever rotates, and is pretty much synonymous with levers. It was Aristotle that said “ Give me a lever and a fulcrum and I shall move the Earth.” The lever pictured is only one kind of lever. There are a total of 3 “classes” of levers. This one is of class One, because the fulcrum is in between the input and output forces. We find examples of all three classes of levers everywhere.

CPO Lever – First Class All The Way This is Investigation 4.2. You can use your handout/Investigation Manual to follow along. The CPO lever is a first class lever. The first thing to do is put two weights on the lever to get it to balance. Notice that you can attach the weights at different places on the lever. The weights are easily attached by slipping a loop of yellow string through the hole in the weight and threading one side of the string through the other. Most people will realize quickly that the two weights must be placed equal distances from the fulcrum. Here we have a first class lever. The fulcrum is between the input and output. Can you get two weights to balance?

Levers in Equilibrium Hang your weights like shown here. Does the lever balance? What variables can be changed to balance a lever? First of all, we don’t have equal #s of weights on each side. Second of all they are at different distances from the fulcrum. Yet the lever balances, or more scientifically, it is in Equilibrium. How could this be? What factors, or variables could be changed to reach equilibrium?

Four Variables in a Lever Amount of Input Force Amount of Output Force Length of Input Arm Length of Output Arm Initially, the terminology of Input vs. Output can be a bit confusing, but here’s the deal- the side you first put weight on will be the Input side, and the side to which you must add weight to balance the Lever will be the Output side. We’re going to assume each individual weight has the same mass, and therefore weighs the same. Therefore, we can easily refer to the Input and Output forces in terms of the # of weights, like 1, 2, or 3 weights. Since each weight must be hung at a particular hanging spot on the lever, and the distance away from the fulcrum is marked right on the hook, figuring out the lengths of the Input and Output arms is simple. Whatever the number on the hook from which you are hanging weight, that is the length of that particular arm.

Lever Challenge Hang weights from the lever and get it to balance. Use only 3 strings, one string per position and string MUST have weight. Do 4 trials and record how many weights to hang and where you hang them. Investigation 5.1 The Lever - Its easy to balance 2 weights on the lever, that comes natural to us. But what about when there are more than 2? For this investigation we are going to balance 2,3,4 or even 5 weights. We are also going to try to use more than just one location on each side of the fulcrum. Try to use two or even three. From the example in the slide, you can see there are many ways to get the lever to balance. Challenge yourself to find four different balancing situations and record them on the chart. The ones on there now are merely examples and they are not allowed to be used. SORRY!

Lever Challenge Investigation 5.1 The Lever - Its easy to balance 2 weights on the lever, that comes natural to us. But what about when there are more than 2? For this investigation we are going to balance 2,3,4 or even 5 weights. We are also going to try to use more than just one location on each side of the fulcrum. Try to use two or even three. From the example in the slide, you can see there are many ways to get the lever to balance. Challenge yourself to find four different balancing situations and record them on the chart. The ones on there now are merely examples and they are not allowed to be used. SORRY!

Lever Concept Hang 1 weight 10 cm from the fulcrum. Where does the output force need to be to oppose our input force? 1 1 Investigation 5.1 The Lever - Its easy to balance 2 weights on the lever, that comes natural to us. But what about when there are more than 2? For this investigation we are going to balance 2,3,4 or even 5 weights. We are also going to try to use more than just one location on each side of the fulcrum. Try to use two or even three. From the example in the slide, you can see there are many ways to get the lever to balance. Challenge yourself to find four different balancing situations and record them on the chart. The ones on there now are merely examples and they are not allowed to be used. SORRY!

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 Investigation 5.1 The Lever - Its easy to balance 2 weights on the lever, that comes natural to us. But what about when there are more than 2? For this investigation we are going to balance 2,3,4 or even 5 weights. We are also going to try to use more than just one location on each side of the fulcrum. Try to use two or even three. From the example in the slide, you can see there are many ways to get the lever to balance. Challenge yourself to find four different balancing situations and record them on the chart. The ones on there now are merely examples and they are not allowed to be used. SORRY!

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. 1 Investigation 5.1 The Lever - Its easy to balance 2 weights on the lever, that comes natural to us. But what about when there are more than 2? For this investigation we are going to balance 2,3,4 or even 5 weights. We are also going to try to use more than just one location on each side of the fulcrum. Try to use two or even three. From the example in the slide, you can see there are many ways to get the lever to balance. Challenge yourself to find four different balancing situations and record them on the chart. The ones on there now are merely examples and they are not allowed to be used. SORRY!

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 several groups of weights ? Sum of Input = Sum of Output (F1 x D1) + (F2 x D2) = (F3 x D3) + (F4 x D4)

TOY Engineers Allow time for students to brainstorm possible design ideas and to plan how they will construct their toys. Once students have built their toys, let them share their creations with the class.

Outcomes Use science Think scientifically Communicate technical ideas Teach all students Be science conscious NOT science phobic

What questions do you have about the CPO Levers? Please have participants fill out address cards during Q&A