Embedded Files
Introduction
Introduction
In this learning sequence we explore another one of our simple machines – the pulley.
Watch the short video that gives you an overview of today’s lesson.
Inquiry question and intentions
Inquiry question and intentions
Inquiry question:
How are pulleys used to make work easier?
Learning intentions:
To explain how different pulley systems make work easier.
To solve problems of lifting loads using different pulley systems.
To analyse experimental results, find relationships and draw conclusions.
Background information
Background information
A simple machine is a device that changes the direction of the force on an object or the size of the force on an object.
Pulleys change the direction of a force. They are used to redirect the tension in a cord or rope. Instead of pushing a load up, you can attach it to a pulley above you and pull down to lift the load.
A pulley system is a collection of one or more grooved wheels over which you loop a cord, rope or chain to make it easier to lift things. The more wheels you have, and the more times you loop the rope around them, the more you can lift. Every pivot point exerts upward force on the system, to decrease the amount of force needed.
Each pulley also increases the distance over which the force is applied. This means that you need to pull the rope through a greater distance (pull it further) to lift the load.
For example a pulley system with two wheels halves the lifting force you need with only one pulley, but you have to pull the rope twice as far to lift the weight the same distance.
Which pulley do you think needs more force to lift the weight?
César Rincón, (CC BY-SA 3.0) (adapted)
By allowing the work to be done in the same direction as gravity (down towards the ground), pulleys allow an object to be lifted with less force. When a number of movable pulleys are used, a larger load can be lifted with a smaller effort.
Activity 1: Investigating pulleys
Activity 1: Investigating pulleys
Task 1 - Levers vs pulleys
Task 1 - Levers vs pulleys
Levers and pulleys are both simple machines.
Complete the Venn diagram to explore how are they similar and different.
Click on the image to open the template in a new tab.
Click on the Use Template button to create a copy for you to edit.
Task 2
Task 2
Watch the video Simple Machines: The Pulley.
You will use the knowledge from this video in Task 3.
Simple Machines: The Pulley
Duration: 6:25
Task 3 - Pulley simulation
Task 3 - Pulley simulation
In this task we will be using the Exploring pulley simulation from the Newpathsonline website to complete an investigation.
You will experiment with different types of pulleys and loads to better understand the mechanical advantage of each pulley.
A pulley or pulley system will only lift a load if the input force is large enough to move the weight of each load.
A pulley with a greater mechanical advantage will make it easier to lift the load.
Click on the image to open the simulation in a new tab.
To complete this investigation you need to use the simulation website and the investigation report at the same time.
Note: It will be easiest to complete the investigation if you have both windows/tabs open and visible on your screen at the same time.
Complete all your work in the Investigation report document.
Click on the button to open a new tab and view the Google Doc activity sheet.
Click on the Use Template button to create a copy for you to edit.
Activity 2: Mechanical advantage of pulleys
Activity 2: Mechanical advantage of pulleys
A student was trying to find out what happens to the force needed to lift a load when you add more pulleys to the system. They did an experiment using pulleys to lift a load of 100N.
The results of their experiment are in the image below.
Your task is to help the student complete their investigation report. Complete the following tasks and questions in the Impact on force investigation report Google Doc.
Use information from the Results image to complete the Table 1.
Answer the questions in the Questions section of the report.
Complete the report by writing a Discussion and Conclusion for this experiment.
Click on the button to open a new tab and view the Google Doc activity sheet.
Click on the Use Template button to create a copy for you to edit.
Activity 3: The impact of friction on pulleys
Activity 3: The impact of friction on pulleys
In machines, the amount of friction in a system can have an effect on the amount of force that is needed to move an object. Friction can act to slow things down or make it harder to move or lift.
Read the following information then complete the questions in the embedded Google Form. (Scroll down the Form to see all the questions.)
Two Year 8 students wanted to compare the friction between a 2 kg mass and four different materials:
carpet
sandpaper
vaseline
powder.
They used four identical ramps. Each ramp was covered with a different material.
Extension - Further explorations
Extension - Further explorations
Task 1 - Pulleys in nature
Task 1 - Pulleys in nature
Did you know that tangle-web spiders use pulleys to subdue big prey?
Find out more about it by reading the short scientific article Spidey crane on the Cosmos website.
Task 2 - Further investigation of simple machines
Task 2 - Further investigation of simple machines
Investigate simple machines, work and mechanical advantage by watching the video Simple machines on YouTube.
Task 3 - Practical applications of pulleys
Task 3 - Practical applications of pulleys
The mechanical advantage in a pulley system is equal to the number of ropes supporting the movable load. This means that we do not just count the number of pulleys or the number of ropes. We need to think about the number of tensioned ropes and whether the pulleys are fixed or movable. List some illustrated instructions for a friend explaining how to work out the mechanical advantage of a pulley system.
Have you ever been to a gym and seen the pulley machines?
Find out how the cable machines with different pulley ratios can be used in exercise.
Handing in your work
Handing in your work
Don't forget to hand in the work you completed today!
Your teacher will have told you to do one of the following:
Upload any digital documents you created and any photos you took of your written work to your Learning Management system (MS Teams, Google Classroom for example).
Email any digital documents you created and any photos you took of your written work to your teacher.
Make sure you keep any hand written work you did in your exercise book or folder as your teacher may need to see these when you are back in class.
Student reflection
Student reflection
Show how do you feel about today’s learning? (smiley faces).
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