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Lesly loja - Pulley Lab physic science
Science Student Teaching Seminar 1 (SEED 4481)
Brooklyn College
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Name: lesly loja Date: 03-15-
Student Exploration: Pulley Lab
Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes.
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?
because it increases the distance you have to pull lightening the load
- In what places have you seen pulleys at work?
Ships, Factories, simulators
Gizmo Warm-up 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 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?
51N
- 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.
A. What force is required to lift a 50-N load with this pulley system? 25N
B. What is one advantage of using a pulley system?
The weight is easier to lift
Activity A:
Mechanical advantage
● 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?
Less force will be needed
- 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.
Pulley system Weight (N) Minimum input force (N) 1 fixed 60 N 61 N 1 fixed, 1 moveable 60 N 31 N 2 fixed, 2 moveable 60 N 16 N 3 fixed, 3 moveable 60 N 11 N
- Summarize: How does the minimum input change as you add more pulleys to the system?
The minimum input went down by a little more than half, as more pulleys were added.
- Analyze: Compare the input force to the number of pulleys in each system. Do you see a pattern? If so, describe it:
When more pulleys are added, the input force is divided almost in half
- Apply: How much force do you think would be needed to lift a 100-N load with a pulley system composed of
two fixed and two moveable pulleys? 26 N
Check your answer with the Gizmo. How much force was actually needed? 26 N
Activity B:
Work and energy
● Select the 1 fixed pulley. ● Set the Weight to 80 N and Efficiency to 100%. ● You will need a calculator for this activity.
Introduction: The law of conservation of energy states that in a closed system the total energy is constant. In other words, energy is neither created nor destroyed.
Question: How does a pulley system demonstrate conservation of energy?
- Observe: Lift the 80-N load with different pulley systems. Notice the length of the rope pile. How does adding pulleys affect the distance you have to pull the rope to lift the object?
the more pulleys you add the less you have to pull
- Gather data: Lift the 80-N load to the top with eachpulley system. In each case, record the input force, input distance, output force, and height. Include units.
Pulley system Input force (N)
Input distance (m)
Output force (N)
Height (m) 1 fixed 80 8 80 8. 1 fixed, 1 moveable 80 16 160 8. 2 fixed, 2 moveable 80 26 320 6. 3 fixed, 3 moveable 80 25 480 4.
- Calculate: When a force is exerted over a distance, work is done on an object. Work is measured in joules (J) and is equal to the product of force and distance: W = F • d. For each pulley system, calculate the input work (input force • input distance) and the output work (output force • height). Units of work are newton-meters, or joules (J).
Pulley system Input work (J) Output work (J) 1 fixed 81 x 8 = 708 J 81 x 8 = 708 J 1 fixed, 1 moveable 41 x 16.8=688 J 82 x 8.4=688 J 2 fixed, 2 moveable 21 x 26 = 562 J 84 x 6 = 562 J 3 fixed, 3 moveable 14 x 25.8=361 J 84 x 4.3=361 J
- Analyze: Work is a measure of energy. Look at each pair of input-output values. How do pulley systems illustrate conservation of energy?
more pulleys =more distance but less work
Extension:
Friction and efficiency
● Select 1 fixed pulley, and set the Weight to 40 N. ● Select the Standard pulleys (5 N). ● You will need a calculator for this activity.
Introduction: So far you have studied “ideal” pulley systems. In the real world, friction reduces the advantage of any pulley system. Efficiency is a measure of how much friction is present.
Question: How does friction affect the mechanical advantage of a pulley system?
- Observe: Use the fixed pulley to lift the 40-N load. Vary the efficiency of the pulley. How does the efficiency of the pulley affect how much force is needed to lift the 40-N load?
once it gets off the ground there is even less force required to move the object
- Gather data: Use the 1 fixed pulley to lift the 40-N load at the following efficiencies. In each case, record the input force and output force shown at bottom right.
Efficiency Load (N) Input force (N) Output force (N)
Ratio (Output ÷ Input)
100% 40 N 41 41 1 75% 40 N 54 40. 67% 40 N 60 40. 50% 40 N 81 40.
- Calculate: Divide each output force by the input forceto find the ratio. Fill in the last column. How does the ratio of output force to input force compare to the efficiency of the pulley?
Ration= efficiency
- Make a rule: Given the input force and output force of a fixed pulley, how do you calculate efficiency?
output/input
- Challenge yourself: An ideal system with one fixed and one moveable pulley has a mechanical advantage of two. Suppose a real system with one fixed and one moveable pulley had an efficiency of 80%. (Recall that a standard pulley has a weight of 5 newtons.)
A. Using this system, how much force will be needed to lift a 45-N load? 33
B. Check your answer using the Gizmo. How much force was needed? 33
C. Modify your efficiency equation from #4 above to factor in mechanical advantage.
output/input+
Lesly loja - Pulley Lab physic science
Course: Science Student Teaching Seminar 1 (SEED 4481)
University: Brooklyn College
