Student Exploration: Pulley Lab
Vocabulary: block and tackle, conservation of energy, efficiency, friction, input force, load, mechanical advantage, output force, pulley, pulley system, simple machine, work
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
A pulley is a wheel with a groove for a rope or cable. The image at left shows an example of a pulley system, also called a block and tackle.
Why do you think people use pulley systems to lift heavy loads?
In what places, have you seen pulleys at work?
The Pulley Lab Gizmo™ demonstrates why pulleys are useful for lifting loads. To begin, check that the Gizmo has the following settings:
The Pulley configuration is 1 fixed.
Ideal pulleys (0.0 N) is selected.
The Weight is 50 N (50 newtons), and the Efficiency is 100%.
To apply an input force, drag the Input force spring balance to the right. Slowly increase the force until the 50-N load begins to rise.
What is the minimum force required to lift a 50-N load with one fixed pulley?
Change the Pulley configuration to 1 fixed, 1 moveable. As you did before, slowly drag the Input force balance to the right until the load begins to lift.
What force is required to lift a 50-N load with this pulley system?
What is one advantage of using a pulley system?
Get the Gizmo ready:
Select the 1 fixed pulley configuration.
Set the Weight to 60 N and Efficiency to 100%.
You will need a calculator for this activity.
Introduction: A pulley is an example of a simple machine. Many simple machines are useful because they allow the user to lift a heavy weight using less force than it would take to lift the weight directly. The mechanical advantage of the machine is a measure of this benefit.
Question: What is the mechanical advantage of each pulley system?
Predict: How will adding more pulleys affect the input force needed to lift the load?Gather data: With the Weight set to 60 N and the Efficiency set to 100%, find the minimum input force needed to lift the load with each system. Fill in the table below. Include units.
Summarize: How does the minimum input change as you add more pulleys to the system?