
Secrets of Lost Empires I—Obelisk


Classroom Activity

Objective
To investigate how levers can be used to lift objects.
 copy of "Lever Loads" student handout
(PDF or
HTML)
 two rulers, 30 cm (12 in.) plastic or lightweight wood
 pencil
 five weights (such as washers or coins)
 tape
 sheet of paper
Let students investigate how levers can be used to lift objects in this activity.
Distribute materials and copies of the "Lever Loads" student handout to
pairs of students.
In Part I students will discover that the amount of
force needed to lift a load changes depending on where the fulcrum is placed.
In Part II students repeat the investigation, this time comparing the
distance the load is lifted to the distance they push down the other lever arm.
After completing the activity, ask students to think about how NOVA team
members used levers to raise the twoton obelisk. Where did they place the
fulcrum (the pivot point) in relationship to the obelisk (load)? Why did the
team need to pack stone and earth underneath the lever to support it?
Archimedes (287212 B.C.E.) understood levers well enough to claim, "Give me a
lever long enough and a place to stand, and I could lift the world." Discuss
this quote with students. What does Archimedes mean by a lever "long enough"?
Where might he place the fulcrum?
In Part I, students will notice that the closer the fulcrum is to the load, the
less force is required to lift the load. There is a point where the fulcrum is
so close to the load that it appears no force is required at all. The weight of
the lever itself (in this case, the ruler) is actually providing the needed
force. This is one reason why crowbars are very heavy.
In Part II, students should note that the position of the fulcrum also affects
how far you push down and how far the load is lifted up. Levers trade force
(how hard you push) for distance (how far you move the load). For example, when
you apply a small force over a long distance, you move the load a small
distance.
Students should notice that when they use less force to lift the load, the
distance they push the lever arm down is larger than the distance the load is
lifted. When they use more force to lift the load, the distance they push the
lever arm is smaller than the distance the load is lifted. When the fulcrum is
placed in the middle of the lever, the distance the load is lifted is about
equal to the distance that the other end of the lever is pushed down. In this
situation there is essentially no mechanical advantage—the distance over which
the force is applied equals the distance the load is lifted.

