Investigation 1 – PreLab
As you look about, you probably see half a dozen machines that you don’t recognize as such. Ordinarily, people think of a machine as a complex device – a gasoline engine or a washing machine. They are machines; but so are a hammer, a screwdriver, a bike’s wheel. A machine is any device that helps you to do work.
Naval architects know that the more weight a boat carries, the lower it sits in the water and the more water resistance it creates. That’s why they design boats with sharp narrow bows. This wedged design allows the boat to push water cleanly out of the way.
This Investigation is designed to help you to answer the following Focus Questions:
- How can simple machines change the force needed to lift a load?
- How does mechanical advantage relate to effort and load forces?
Note: These questions are located in your SDR at the beginning and end of the Investigation.
As a class, read the Background(s) in the Investigation. When finished, discuss the following concept as a class:
- A pulley is one type of simple machine. It consists of a small wheel with a groove that a rope or string can slide over.
- Pulleys can be fixed to an immovable object or they can be freely floating.
- When pulleys are discussed in scientific terms the mass that is to be lifted is called the load force.
- The length of rope or string that extends from the load to the pulley is called the load distance.
- The force that is applied to the rope or string to lift the load is called the effort force.
- The length of rope or string from the pulley to where the effort is applied is called the effort distance.
- Although work may seem easier if a simple machine is used, machines do not decrease the amount of work done.
- Mechanical advantage describes the relationship between the effort force (force needed to lift the load) and the force of gravity on the load (load force). This can be expressed mathematically by the following equation.
- Mechanical Advantage = Load Force ÷ Effort Force
- The amount of work done to lift a load may “seem easier” if a machine offers a mechanical advantage greater than 1.
LEARN THE LabLearner LINGO
The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.
- load force
- load distance
- effort force
- Joule (J)
- mechanical advantage
SET FOR SUCCESS
- Complete the Recall section in your SDR.
- What is mechanical advantage?
- Do pulleys change the amount of work done to lift a load?
- Do one and two pulley systems provide the same mechanical advantage?
- As a class, think of what you already know about simple machines. Generate examples of types of simple machines you might encounter at home or at school.
Note: Simple machines are devices that make work seem easier to perform by changing the distance over which a force is applied to a load and by changing the direction in which the force is applied. Examples you may think of might include wheelbarrows, crow or pry bars, hammers, see-saws, playground slides, wheels and axles on a car, gears in a mechanical clock, bicycle gears, arms, legs, hips, shoulders, bottle openers, pull tabs on drink cans, wheelchair ramps, inclined driveways or sidewalks, garlic presses, jar lids, bottle caps, screws, doors, doorknobs (lever and round), hole punch, pliers, wrenches, and a block and tackle.
- As a class, try to classify how the machines listed above could be grouped based on their mode of action.
Note: Wheelbarrows, crow or pry bars, see-saws, arms, legs, bottle openers, pull tabs, garlic presses, lever doorknobs, doors, the hole punch, pliers, and wrenches are levers. Round doorknobs, wheels and axles on cars, gears in mechanical clocks and bicycles, shoulders, and hips are all examples of wheels and axles. Wheelchair ramps, inclined driveways and sidewalks, screws, bottle caps, and jar lids are inclined planes. A block and tackle is a pulley system.
- Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful.
- After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.
Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.
Note: Homework is posted below the video.
Be sure to review the Investigation and video in preparation for the Lab.