Published on May 25, 2017
Up It Goes
The objective: A Wheel and Axle are connected to two pulleys lifting an elevator containing a load. We are trying to figure out if it would be easier to pull up the elevator with the wheel and axle or just the string.
A pulley is a simple machine that has a rope or string wrapped around a wheel with a groove through it. One end of the string is attached to a weight and the other end you hold. Pulleys can make lifting a load easier. Elevators are a good example of the use of a pulley system.
A block and tackle consists of at least two pulleys, which is basically the pulley system. Having two pulleys will allow you to lift the load with less force. This is also called mechanical advantage. However the trade off in having to use less force or having a mechanical advantage is that you have to pull the rope a farther distance than if you had used just one pulley attached to your load. The more pulleys that you have, the less force will be used. When you only have one pulley, you don’t have the rope going as far as you do with using two or more pulleys. But when using one pulley you will have to pull harder because it won’t reduce the amount of force needed to lift the load. Using one pulley won’t give you any mechanical advantage and you will have to use the same force as the weight.
For example, if I have a 300 lb weight, attached to one pulley, I will need to use 300 lbs of force to lift the 300 lb weight. But if I had two pulleys (or a block and tackle) then it would reduce the force required to lift the weight to 150 lbs. The trade-off is that I have to use twice the amount of rope to lift the weight. This is because I would have to pull more string than I did with the one pulley because the rope has to go through all the pulleys and you have to bring the rope through. So if I used four pulleys to lift the 300 lb weight, I’d have to use 75 lbs of force, but the trade-off is I have to use four times the amount of rope.
The mechanical advantage is increased by using more pulleys to lift up the weight. Using all these pulleys decreases the amount of force being used, but increases the amount rope being pulled.
We have made an elevator. The question we're proposing is if it will be easier to lift the 5 pound weight with 1 or 2 two pulleys.
Our Hypothesis is that using a compound machine, (elevator) we will be able to pull up the weight easier using the pulleys rather than doing it with the string and with a block and tackle. We think that two pulleys will be easier to pull the weight.
• Gauge (measure force)
• Nylon rope
• 5 pound weight
• Clothes rack
• Fishing reel
• Screw driver
Step 1: Take out the clothes rack and put the bottom parts together.
Step 2: Once the clothes rack is standing up by itself, attach the top part on to the sides.
Step 3: Open the nylon cord bag and cut a piece that is about 1 foot
Step 4: Use the that piece of nylon cord to attach 1 of the pulleys to the top of the rack (tie it in the middle)
Step 5: Attach the fishing reel to the side of the clothes rack.
Step 6: Screw the clamps onto the structure’s side holding the fishing reel up.
Step 7: Cut a piece of nylon cord that’s around 130 cm long and then thread it through an upside down pulley.
Step 8: Attach the upside down pulley to the 5 pounds with another piece of nylon cord that’s 1 foot long.
Step 9: Take the other side of the rope and tie it to the top left corner of the clothes rack and then tape it to make sure it doesn’t move.
Step 10:Cut the rope on the other end and then tie it to one end of the gauge. Use the string you cut off and tie it to the other side of the
Step 11: Hold the rubber band in the reel and tie the end of rope through it. Wrap it around until the rope is tight.
Step 12: Follow the procedures and have fun experimenting!
Step 1: Take the string out of the reel and pull it to see how much force you are using with two pulleys.
Step 2: Read the gauge to see how much force has been used.
Step 3: Record the number shown on the gauge.
Step 4: Repeat Step 1 - 3 three times.
Step 5: With the weight resting on the ground, measure the rope between the pulley and the end of the rope.
Step 6: Pull the weight to the top and take the measuring stick and measure from the pulley to the end of the rope again. Repeat step 5- 6 three times.
Step 7: Repeat step 1 - 6 except this time, use only one pulley.
Step 8: Once you have recorded all the information, look at them, record any differences and write the observation.
It turned out that it was easier to use two pulleys rather than one. Our hypothesis was right! When we did the experiment there was always one measurement that was the same so we always had one that was the more accurate result than the other. In conclusion It’s easier to use at least two or more pulleys than just one.
• Powerful Pulleys. Teachengineering.org. April 10, 2014. http://www.teachengineering.org/view_lesson.php?url=collection/cub_/lessons/cub_simple/cub_simple_lesson05.xml.
• Brian, Marshall. How a Block and Tackle works. howstuffworks.com. April 9, 2014. http://science.howstuffworks.com/transport/engines-equipment/pulley.htm
• Weinberg, David. The mechanical advantage of a block and tackle. ehow.com. April 9, 2014. http://www.ehow.com/about_6120885_mechanical-advantage-block-tackle.html
• Frank B. Chavez, What can a pulley do to make life easier? ehow.com. April 9, 2014. http://www.ehow.com/facts_7607772_can-do-make-life-easier.html
Science Fair Project done By Anna and Grace