Home Project Ideas Project Guide Ask An Expert Blog Careers Teachers Parents Students

Give Yourself a Lift: Lightening the Load with Pulleys

Difficulty
Time Required Short (2-5 days)
Prerequisites None
Material Availability Readily available
Cost Low ($20 - $50)
Safety Adult supervision recommended

Abstract

Before the Industrial Age, people relied on muscle power for moving and lifting heavy objects. Here's a project that shows you how you can use your head to make heavy lifting easier on your muscles–and your back!

Objective

The goal of this project is to measure the force and the work required to lift the same load with different arrangements of pulleys.

Credits

Andrew Olson, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Give Yourself a Lift: Lightening the Load with Pulleys" Science Buddies. Science Buddies, 30 June 2014. Web. 31 July 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/ApMech_p010.shtml>

APA Style

Science Buddies Staff. (2014, June 30). Give Yourself a Lift: Lightening the Load with Pulleys. Retrieved July 31, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/ApMech_p010.shtml

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.


Last edit date: 2014-06-30

Introduction

Pulleys are machines that make the job of lifting objects easier. A simple pulley (see Figure 1) consists of a single wheel, mounted on an axle and held in a small frame.

Illustration of a simple pulley.
Figure 1. Illustration of a simple pulley. The simple pulley changes the direction of the applied force.

The edge of the wheel has a channel, through which a rope can pass. The pulley can be used to lift an object, as shown in Figure 1. Here one end of the rope is fixed in place (top right) and the object to be lifted is attached to the pulley. Pulling on the other end of the rope lifts the object.In another arrangement (not shown), the pulley is fixed in place (e.g., to an overhead beam) and the rope passes over the pulley. One end of the rope is attached to the object. By pulling down on the other end of the rope, the object is lifted.

Two (or more) pulleys can be arranged to work together as shown in Figure 2. This is an example of a compound pulley arrangment.

Illustration of a compound pulley.
Figure 2. Illustration of a compound pulley.

One end of the rope is fixed to the upper pulley, as shown above. The rope passes around the lower pulley, and then around the upper pulley. The object to be lifted is attached to the lower pulley. By pulling down on the rope, the object is lifted.

A block and tackle is an arrangement that uses multiple pulleys mounted on the same axle. The pulleys are the "blocks" and the rope is the "tackle." An example is shown in Figure 3.

Illustration of a block and tackle.
Figure 3. Illustration of a block and tackle.

In Figure 3, both the upper and the lower block have two pulleys on the same axle. The object to be lifted is attached to the lower block. One end of the rope is fixed to the upper block, and then passes around the first pulley in the lower block. Next, the rope passes over the first pulley in the upper block, then down to the second pulley in the lower block. Finally, the rope passes over the second pulley in the upper block. As with the compound pulley shown in Figure 2, pulling down on the rope raises the object.

What is the point of connecting multiple pulleys into a compound pulley or block and tackle arrangement? How about building them for yourself to find out?

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

  • simple pulley,
  • compound pulley,
  • block and tackle,
  • force,
  • work,
  • mechanical advantage,
  • energy conservation.

Questions

  • How does physics define the term, work?
  • What are the SI units for force?
  • What are the SI units for work?

Bibliography

Materials and Equipment

To do this experiment you will need the following materials and equipment (you should be able to find these things at your local hardware store):

  • tape measure,
  • spring scale (Note: if you can't find this at your hardware store, try a sporting goods store—they're often used for weighing fish—or the Internet),
  • 3 pulleys and 2 blocks,
  • rope (must fit pulley channels and must be strong enough to lift the desired weight),
  • an object to lift (e.g., 5-gallon bucket with sand or water).

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.

Experimental Procedure

Safety note: This project involves lifting objects using ropes and pulleys. Minor injuries are possible but can easily be avoided with proper caution. Adult supervision recommended.

  1. Do your background research and make sure that you understand the terms and concepts.
  2. Study the diagrams in the Introduction so that you know how to assemble the various pulley arrangements yourself.
  3. Find a place to firmly and safely attach your pulleys (e.g., an overhead beam in the garage, or basement). Make sure you have permission. Get help from an adult if needed. Remember that the attachment point must be able to bear the weight that is to be lifted by the pulley arrangement.
  4. Fill your bucket with water or sand and weigh it by hanging it from the spring scale. You want to have enough sand or water so that the spring scale reads near its maximum weight (or force).
  5. Lift the bucket using the simple pulley. Attach one end of the rope to the bucket. Attach the other end of the rope to the spring scale. Pull on the scale until you lift the bucket off the ground. Record the scale reading in your lab notebook.
  6. How much rope do you have to pull through the simple pulley in order to lift the bucket 2 meters? Record the length in your lab notebook.
  7. Lift the bucket using the compound pulley arrangement. Attach the bucket to the lower pulley. Attach the spring scale to the free end of the rope. Pull on the scale until you lift the bucket off the ground. Record the scale reading in your lab notebook.
  8. How much rope do you have to pull through the compound pulley in order to lift the bucket 2 meters? Record the length in your lab notebook.
  9. Repeat steps 7 and 8 with the block and tackle.
  10. Make a table of your results. Calculate the mechanical advantage of each pulley arrangement and include it in your table.
  11. If your scale is calibrated in units of weight, you can easily convert to units of force (N, Newtons) by multiplying the weight (in kg) by 9.8 m/s2.

Questions

  1. What pulley arrangement makes it easiest to lift the bucket?
  2. How much work is required to lift the bucket an equal distance with each pulley arrangement?
  3. How does the mechanical advantage of a pulley system relate to the length of rope required to lift the object a fixed distance?

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.


Variations

  • Can you predict how much force would be required to lift your bucket if the blocks in your block and tackle each had three pulleys? Try it and see if your prediction is correct.

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.

Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Ask an Expert

Related Links

If you like this project, you might enjoy exploring these related careers:

Mechanical engineer building prototype

Mechanical Engineer

Mechanical engineers are part of your everyday life, designing the spoon you used to eat your breakfast, your breakfast's packaging, the flip-top cap on your toothpaste tube, the zipper on your jacket, the car, bike, or bus you took to school, the chair you sat in, the door handle you grasped and the hinges it opened on, and the ballpoint pen you used to take your test. Virtually every object that you see around you has passed through the hands of a mechanical engineer. Consequently, their skills are in demand to design millions of different products in almost every type of industry. Read more
female mechanical engineering technician

Mechanical Engineering Technician

You use mechanical devices every day—to zip and snap your clothing, open doors, refrigerate and cook your food, get clean water, heat your home, play music, surf the Internet, travel around, and even to brush your teeth. Virtually every object that you see around has been mechanically engineered or designed at some point, requiring the skills of mechanical engineering technicians to create drawings of the product, or to build and test models of the product to find the best design. Read more

Looking for more science fun?

Try one of our science activities for quick, anytime science explorations. The perfect thing to liven up a rainy day, school vacation, or moment of boredom.

Find an Activity