© The Norwood Science Center 2004
The Norwood Science Center
Forces
Grade 3
Background Information:
In this lesson, students will construct and manipulate a lever.
As they investigate the use of this simple machine, they will identify
variables that affect its performance.
A lever is a rigid bar that is free to turn around a pivot point.
The pivot point is called the fulcrum. A force is applied to one end
of the lever. This force causes an object on the other end of the lever
to move. The object to be moved is called the load. A seesaw is a
type of lever. The plank of the seesaw is the rigid bar. The support
for the plank is the pivot point, or fulcrum. The force is the person on
the end of the seesaw that is up in the air. The load is the person on
the end of the seesaw that is on the ground.
There are three classes of levers. The students will be
investigating a first-class lever. A seesaw is an everyday example
of this class of lever. In first-class levers, the fulcrum or pivot point is
located between the force and the load as shown below.
http://www.fog-ware.com/ScienceAtHome/images/Lever1A.jpg
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© The Norwood Science Center 2004
TITLE:
LEVERS
PURPOSE:
Construct a first-class lever
Test hypotheses related to a first-class lever
MATERIALS:
(per pair)
One pencil
One 3-oz. paper cup with string handle
S-hook
One plastic ten gram mass
Bag of gram cubes
Half-meter stick with string loop at 50 cm end
Pencil
Science journal
Two (2) worksheets
PROCEDURE:
01.
Ask students, How could you lift your science teacher? Permit
them to speculate and share their ideas.
02.
Write the word work on the board. Ask students the following
questions:
What is work?
Would it take work to lift your science teacher?
03.
Explain to students that work is done when a force (push or
pull) causes an object to move or change direction.
04.
Point out to students that a seesaw is a machine that could be
used to lift your science teacher. If certain changes were made
to the seesaw, you could lift Mrs. Ross – even Mr. Haffey!
05.
Arrange the students in teams of two. Distribute a worksheet to
each student and staple the worksheet in his or her notebook.
06.
Explain to students that we will be constructing a simple
machine called a lever that will look very similar to a seesaw.
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© The Norwood Science Center 2004
07.
Distribute half-meter stick to each team.
08.
Students are to place the half-meter stick horizontally on one
desk so the 50-centimeter end is hanging over the edge at the
45-centimeter mark.
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© The Norwood Science Center 2004
09.
Distribute the pencil.
10.
Students should place the pencil under the half-meter stick at
the 30-centimeter mark. Explain to students that the pencil will
act as the pivot point or fulcrum because their lever can move
around this point.
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© The Norwood Science Center 2004
11.
Provide each team with an S-hook.
12.
Have students place the S-hook on the string loop found at the
50-centimeter end of the half-meter stick.
13.
Distribute one 3-oz. paper cup to each team.
14.
Instruct students to hang the cup onto the S-hook using the
string handle.
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© The Norwood Science Center 2004
15.
Distribute the 10-gram plastic mass.
16.
Students should place the 10-gram mass on the half-meter
stick at the zero-end placing the mass so it is completely on the
stick.
17.
Distribute a bag of gram cubes and worksheets to each team.
18.
Students are to add gram cubes ONE AT A TIME to the cup
until the end of the half-meter stick where the 10-gram mass
rests lifts off the table.
19.
Students are to record this Effort (number of gram cubes) on
their worksheets.
20.
Instruct students to remove the gram cubes from the cup and
place them back in the bag.
21.
Have the students carefully move the fulcrum to the 29-cm
mark and repeat steps #18 and #19.
22.
Students should continue this process until the fulcrum is
placed at the 25-cm mark.
23.
(optional): If time permits, students could repeat the
experiment to obtain a second set of data.
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© The Norwood Science Center 2004
CONCLUSION:
01. Ask students if they notice any change in the Effort (number of
gram cubes) needed to lift the Load (10-gram mass) as the
fulcrum is moved closer to the Load (10-gram mass). Hopefully
they will recognize as the fulcrum moves to the Load, the Effort
decreases.
02.
Have students write the following in their notebook:
Load = the item to be lifted (the 10-gram mass)
Effort = the amount of force needed to move the load (gram
cubes)
Fulcrum = pivot point (pencil)
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© The Norwood Science Center 2004
Distance
Effort
Distance
Effort
Load to Fulcrum
(g)
Load to Fulcrum
(g)
(cm)
(cm)
30
30
29
29
28
28
27
27
26
26
25
25
Distance
Effort
Distance
Effort
Load to Fulcrum
(g)
Load to Fulcrum
(g)
(cm)
(cm)
30
30
29
29
28
28
27
27
26
26
25
25
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