Investigation 12A: Levers

Essential questionsHow can a lever be used to multiply force?
How does the work done vary with levers?
The lever is a simple machine with many applications. The most common use is to lift heavy objects, but not all lever designs increase the force applied! In this investigation you will use a see-saw to determine the ways in which a lever can be used to increase force.
Part 1: Building a first class lever

Equipment setup for the lever
  1. Build the first class lever as shown.
  2. Hang one mass at 20 cm and the other at 40 cm from the fulcrum on opposite sides.
  3. Adjust the masses until the lever "balances."
  4. Use a spring scale to measure and record the weight of each mass and also record the distance d between each mass and the fulcrum.
  5. Set up levers in which the ratio of input force to output force (mechanical advantage) is 3, 4, 1/2, and 1/4
  1. Propose a model of the form:
    input force = (?) × output force.
  2. Use your data to test your model. How do the measured and predicted ratios compare?
  3. Suggest an explanation for any differences.
Part 2: Building a second and third class lever

Other configurations for the leverThere are three fundamental ways to configure a lever. The second and third class levers have the input and output force on the same side of the fulcrum.
  1. Design and construct a second class lever with a mechanical advantage of three. Use the hanging weight as the output force (load) as shown in the diagram. Measure and record the actual mechanical advantage using a spring scale.
  2. Design and construct a third class lever with a mechanical advantage of 1/3. Use the hanging weight as the output force (load) as shown in the diagram. Measure and record the actual mechanical advantage using a spring scale.
  1. How are the forces applied different from the forces applied in the first part? (Hint: Force is a vector!)
  2. For this part and the previous one, draw diagrams to describe the three different configurations for the relative positions of the fulcrum, applied force (“effort”), and resistance force (“load”).
Read the text aloud

336Previous Page Next Page