Levers and Pulleys
Expectations
Your behavior should mirror the behavior of a scientist this week.
You will be graded on:
Your notes
Your ability to work successfully with a partner
Your scientific behavior during the labs and experiments
The reading and answering questions
Your final test
Remember, if I have to speak to you about your behavior, that is minus 10 points from your behavior grade each time!
Thoughts about levers and pulleys
Archimedes, a Greek mathematician (287-212 B.C.E) worked with levers and pulleys. He said, "Give me a place to stand and a lever of sufficient length and I will move the Earth."
Your mission
How can I lift my teacher in the classroom only using one hand?
Write a hypothesis for your mission in your science notebook.
Review: what is a hypothesis?
Real World Levers
Can you lift me off the floor using only one hand?
Can you crack a walnut, cut paper, or open a bottle or can with your bare hands?
The answer is...not likely without the help of some tools.
Many of the tools I've shown you are called levers.
Science Notes:
Levers are tools that people use to make work easier. Levers are used to lift things or to overcome resistance. Levers give us an advantage by making work easier.
Today we will use levers to find out how they make work easier.
Lever Set Up (pg. 13)
Lever arm = stick or beam, free to pivot at a point
Fulcrum = point around which the lever arm pivots
Load = mass lifted by the lever
Effort = force (push or pull) needed to lift or move the load
Work in pairs.
Getter needs:
dowel
2 pieces of duct tape
binder clip
half meter stick
eraser
load
rubber band
10 minutes to set up and explore with your partner.
Day 2: Lever Challenge
Set up a lever system with the load hanging at 15 cm.
-Can you lift the load using only one finger?
-Does it always take the same amount of force to lift the load?
-Where should you press to lift the load with the least force?
Explore with your partner for 10 minutes.
-What advantage can be gained by using a lever to lift a load?
-How can you measure the advantage provided by a lever?
Did anyone think about using a scale?
Spring scales can be used to measure how much effort is needed to lift the loads.
Notes: Effort is a force, and force is measured in newtons.
Rules for spring scales:
-Always zero the scale before starting.
-Always use the scale right side up, never upside down.
-Pull until the lever arm is level, then read the effort.
-Always stop before the scale goes past the 10 N limit.
Getter can get one spring scale per pair.
Spring scales (pg. 16)
How to read a Spring scale.
Your job: use the spring scale to find out if the load is easier to lift when the effort is applied close to or far from the fulcrum.
Don't move your load! Move the scale and read the effort for 20, 15, 10, 5, and 2.5 cms.
Question: How can you use a lever to get the greatest advantage?
Read pages 1 -4 and do # 1 - 10.
Day #3
Review:
What are the 4 parts of a lever system?
In what ways can a lever provide an advantage?
What is the relationship between the load and effort that gives a lever user the greatest advantage?
What do we measure force in?
Getter can get materials for a lever system. Set up your system and review its parts for a few minutes. Remember to zero out your scale each day!
LEVER EXPERIMENT A SHEET
The load always stays at 10 cm. The load does not move.
The effort moves. It is applied at various 5 cm intervals from the fulcrum.
Directions for experiment:
Record the effort needed to move the load in the chart.
Teacher demonstration and scale discussion(pg. 21)
LEVER EXPERIMENT A GRAPH
What is the x axis showing? The y axis?
What interval should we use for x? For y?
Let's graph our data, then connect the data points to make a curved line.
What can you state about the graph?
What is the relationship between the load and the effort in a lever system?
After experiment discussion:
Did the lever give you any advantage?
Notes: Advantage = any benefit you can get from using a lever.
Did the amount of force needed to lift the load change when you moved the position of the effort?
What is the relationship between the position of the effort and the amount of effort needed to lift the load?
Look at "Response Sheet - Levers" and complete with your partner.
read pages 5 -6 and do #1-10
Day #4: Lever Experiment B
Review yesterday's experiment:
What is the relationship between effort and load?
What are the 4 parts of a lever system?
What advantage do levers provide?
What if we changed yesterday's experiment?
What would happen to the effort needed to lift the load if...
-the scale stayed in one place, and
-the load moved farther and farther from the fulcrum?
Would the result be the same as moving the location of the effort (like we discovered yesterday)?
So in today's experiment, the scale will stay in one place and the load will move. Share your hypothesis.
Lever Experiment B
Let's form our graph.
What does the x axis represent? the y axis? Let's label our intervals.
Remember, in today's experiment the LOAD moves. Graph what you find. Be sure to add 0.5 N. Draw a line connecting your data points when you have finished the experiment.
After the experiment, compare Lever Experiment A and B graphs. How do they compare?
What is the relationship between the location of the load and the effort it takes to move it?
Notes: The effort needed to lift the load decreases as the load gets closer to the fulcrum. The effort increases as the load gets farther from the fulcrum.
Read pages 7-9 and answer the questions #1-6 in your packet.
Day #5
Discussion (pg. 10)
Prepare your lever arm. This lever has the fulcrum right in the middle of the lever arm. Is the fulcrum always right in the middle of the lever arm? What might happen of the fulcrum was not in the middle? Would it still be a lever? Is there any advantage of moving the fulcrum?
Explore these questions with your partner.
What did you discover?
We've been working with class 1 levers.
See diagrams page 11.
Work with your partner to see if you can set up a different kind of lever system. Try to find out what advantage (if any) it provides.
Lever diagrams.
Practice setting up each of the 3 classes of levers. Does one provide a greater advantage?
3 classes of levers
F = fulcrum L = load E = effort
"FLE - 1-2-3! It's easy as 1-2-3!"
The F, L, and E, stand for the part of the lever system that is in the middle of the lever.
Notes:
Class 1 levers have the fulcrum in the middle and the load and effort at the ends.
Class 2 levers have the load in the middle and the fulcrum and effort at the ends.
Class 3 levers have the effort in the middle and the load and fulcrum at the ends.
Read pages 10 and 11 and answer questions #1-5.
Day #6
Review: How many types of levers are there? Why do we use tools?
"Levers at Work" page.
What happens to the effort required to lift a load as the load moves closer and closer to the fulcrum in a class 1 lever, a class 2 lever, and a class 3 lever?
"Lever Pictures A and B" page.
Read pages 12 - 13 and do # 1-3, and pages 14 and 15 #1-4.
Day #7
Think: If you were on a construction site and needed to lift a steel girder to the fifth floor of a building, you would need the world's biggest lever. Not too practical! Levers provide an advantage, but they aren't appropriate for all jobs. It would make more sense to use a pulley.
Getters need:
heavy book from your desk
binder clip
half meter stick
1 piece of duct tape
1 looped rope
1 pulley
1 load
Investigate: Can a pulley be used to lift a load?
Single fixed pulley vs. single moveable pulley (pg. 12)
Which pulley system provides an advantage? How can we measure it?
"Pulley Diagrams" sheet. Discuss (pg. 13)
Getter: get a spring scale.
Your job is to build a fixed pulley system AND a moveable pulley system, measure the effort, record it, and answer the question in part 1.
Notes
Pulley = a wheel with a grooved rim in which a rope can run to change the direction of the pull (force) that lifts a load.
Fixed pulley = has a wheel that is attached to something above the load
Moveable pulley = has a wheel that is attached to the load.
Mechanical advantage = reduces the effort (force) needed to lift a load
Directional advantage = a change in direction that results from passing a rope through a pulley
Day #8
Review:
How are fixed and moveable pulleys the same?
What kind of advantage is provided by each pulley system?
In what ways are pulleys and levers the same?
Is there any advantage to using 2 pulleys at the same time?
Getters: please get:
a heavy book from your desk
1 half meter stick
1 binder clip
1 rope
2 single pulleys
load
duct tape
Need a hint? (pg. 18)
"Pulley Diagrams" sheet part 2. (pg. 19)
Notes:
Levers and pulleys are examples of simple machines.
Simple machines are devices to make work easier.
The 6 simple machines are:
levers
pulleys
inclined plane
wedge
screw
wheel and axle
Simple Machine: GEARS
Gears are similar to pulleys, but with teeth. They can change direction. They have an axle and can be simple or compound. They provide mechanical advantage.
Be sure to watch "The Science of Disney Imagineering - Levers and Pulleys" (located in the P drive, Maloney, science)