Sample Lesson from Build It Up
What Can You Do With a Lever?
Introduction
In this lesson: Children study common levers and identify
how they make work easier for people.
Specific Expectations
Children will have opportunities to:
•
describe, using their observations, the changes in
the amount of effort needed to lift a specific load
with a lever when the position of the fulcrum is
changed (3s75)
• describe, using their observations, how simple
levers amplify or reduce movement (3s76)
• communicate the procedures and results of
investigations for specific purposes and to specific
audiences, using demonstrations, drawings, simple media works, and oral and
written descriptions (3s82)
• design and make a levered mechanism (3s85)
• identify a number of common levers and describe how they make work easier
(3s92)
Also: 3s80
Assessment
•
•
•
•
Invite children to find a lever at home and explain to their family what it does and
how it makes work easier. Ask children to bring their levers to school, if possible.
(3s82, 3s92)
Children can use Reproducible 12A: Life With a Lever on page 70, to describe
how they would lift three people on a seesaw. Do they understand how changing
the location of the fulcrum in a lever changes the effort required to lift a load?
(3s75, 3s76)
Ask children to draw a picture of the lever they studied in the Exploration, and
ask them to label the fulcrum and lever arm. Invite them to describe, in pictures
or words, how the lever helps people do work. (3s80, 3s92)
In Extending Learning, children can design and build a balance. Reproducible
12B: Design and Build a Balance on page 71, will help them follow the steps in
the design process. Invite them to explain their balance to a friend. (3s85)
Getting Organized
Materials: levers
Suggested Grouping: class and small groups
Suggested Time: Activate, 20 minutes; Explore, 20 minutes; Apply, 15 minutes
Advance Preparation: For Activate, work outdoors with a real seesaw, or make a
seesaw in class: tape a can or rolling pin to a desk and place a piece of wood or
cardboard on it. Use soup cans or books as weights. For Explore, collect a number of
common levers.
Safety
Establish safety procedures before distributing levers. For example, children should
ensure that no one's fingers are near the lever before they use it. Use your discretion in
deciding whether children can safely use certain common levers, e.g., nutcrackers.
Content Background
Levers are simple machines (tools) that help people do work. Every lever has a rigid
arm and a fulcrum (or pivot). The fulcrum is a stationary point either on the lever or at
the place where the lever rests. The rigid arm moves around the fulcrum. To make a
lever work, the person using it does work. This work is called the effort. The load I what
the lever helps a person to move or to overcome. In a balance, the load is the object
being weighed. In a nutcracker, the load is the resistance of the shell to cracking.
Levers can amplify force or movement. It takes a great deal of effort to remove the cap
from a bottle with your hands. Think of how much easier it is when you use a bottle
opener. The bottle opener takes your effort (pushing up) and amplifies it to overcome
the resistance of the bottle cap.
Levers can also reduce force of movement. When you use tweezers, a small movement
of your fingers produces a longer movement of the tweezer tips, to grab and remove the
hair.
Many everyday items, such as scissors, pliers, tongs, and tweezers, have to lever arms.
They are called compound levers. The fulcrum in these items is the place where the two
lever arms are joined.
All levers fall into three basic classes. Lever classes are characterized by the position of
the fulcrum, load, and effort. For example, all first-class levers have the fulcrum located
between the load and the effort. First-class levers include seesaws, balances, and
crowbars.
When you move the fulcrum, you change the amount of effort needed to do work. You
can move or lift a greater load with the same effort if the load is closer than the effort to
the fulcrum. For example, a person on a seesaw can lift two people if the two people sit
closer to the fulcrum than the single person. Wheelbarrows help us to lift heavy items
because the load is closer than the effort (our hands) to the fulcrum (the wheel). The girl
in this picture could lift a bigger rock with the same effort if she moved the fulcrum
closer to the rock.
Activate
Use a playground seesaw to explore how levers work. Ask two children to get on and
demonstrate how the seesaw works. Then invite different children to get on in different
combinations, and see what happens. Ask,
•
What happens if one very small student, and one very tall student get on?
•
What happens if two students get on one side and one student sits on the other
side? How can the single student lift the other two students?
Introduce the terms lever and fulcrum. Point out the fulcrum in the seesaw and help
children to see that to lift a heavier weight, you need to move the weight closer to the
fulcrum (i.e., you change the position of the fulcrum).
Look at the photographs and read the captions on page 26. Reinforce the idea that the
items pictured are all levers. Even though they do not look the same, they all help us to
do work. Ask children to identify some of the levers you have collected, and which they
will be using the Exploration.
Considering the ESL Learners
Have as many actual levers on hand as possible. Hold up each lever when you are
discussing it. To help children understand what a fulcrum is, point out the fulcrum in the
different levers or ask children to identify it for you.
Preconceptions
Children may think that a lever is a specific item, such as a seesaw. Doing the
Exploration will help them to understand that many items are levers.
Explore
Read the Exploration together. As a class, choose one lever and examine it together.
Do steps 1-3 of the Exploration together: answer the questions asked in each step and
record the answers in the class Science Journal. The questions are:
• What is the lever? Who uses it?
• What does the lever do? Can you do the same things without using your lever?
• Which parts of your lever move when you use it? What do you do when you use
a lever (do you push, pull, lift)?
Exploration: See how levers work.
1-3. Distribute a different lever to each group and ask children to answer the Exploration
questions for their lever. You may have to help some groups with step 2: identifying
what their lever does and thinking about how they can or cannot do something without
using it. For example, can they crack a nut without using a nutcracker? Ask children to
record the answers to the questions in their Science Journals.
4. Invite each group to explain their lever to the rest of the class. Discuss how the
different levers help us do work.
Exploration Results
After examining and using their lever, children should be able to explain what that lever
does and how it helps make work easier.
Apply
Review with children what a fulcrum is and ask them to identify the fulcrum in the lever
they studied in the exploration. If children have not noted the two lever arms in some
levers, point them out now. Compare the different levers. Ask: How are these levers the
same? How are they different? Children should notice that all levers have a fulcrum and
that they all help us do work. Accept any other answers that children can justify. Among
the differences, children may mention shape, colour, and size. They may also notice
that people do different kinds of work when they use a lever (e.g., pushing, squeezing),
and that they position of the fulcrum and the effort change.
Introduce the terms effort and load and identify together the position of the effort and the
load in the levers children used.
Curiosity Place
The shadoof is a levered water-lifting machine invented hundreds of years ago and still
used in simple irrigation systems near the Nile River in Egypt. It is composed of a long
suspended rod with a bucket on one end and a weight on the other end.
Extending Learning
Invite children to design and build a simple balance. First, look at the classroom balance
and ask children to explain how a balance works, and how it is a lever. Invite them to
point out the lever arm and the fulcrum. Distribute Reproducible 12B on page 71 to
remind children of the stages in the design process.
Think!
To help children answer this question, ask them to lift a thick book or dictionary without
bending their elbow. Now ask them to lift it with a bent elbow. Which way is easier?
(lifting with a bent elbow) How does their arm feel when they lift the book the easier
way? (they should feel the muscles in their arm squeezing) When you bend your elbow,
your arm works like a lever and it is easier to lift the book. Your muscles provide the
effort, your elbow acts as a fulcrum, and the books are the load.