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See Saw

Change the position of the fulcrum in a large see saw and feel how the forces change.
Science content (2016 curriculum): 
Physics: Motion and Forces, Newton’s Laws, Gravity (K, 2, 6)
Physics: Simple and complex Machines (5)
Science topic (2005 curriculum connection): 
Physical Science: Force and Motion (grade 1)
Physical Science: Forces and Simple Machines (grade 5)
Lessons activity is in: 
  • lever arm: long plank of wood. 1m long is more manageable and several can be set up in a classroom. Long plank e.g. 2x6 is dramatic, but is harder to manage.
  • load: brick for shorter levers; heavy concrete block/crate containing concrete blocks for longer levers
  • if necessary, duct tape to secure brick/concrete block to the end of lever
  • fulcrum: paint roller for shorter levers, a split log of wood for longer
  • optional: ruler or tape measure

Before class, set up the see saw with the fulcrum positioned so that students will just about be able to tip the load up.

Ask a pair of students to experiment with the see saw. (The objects are heavy, so the students should work slowly and carefully with good communication within the pair). Prompt the students to move the fulcrum and see what difference it makes.
They should find that when the fulcrum is near the load, it is easy to push it up in the air, but when it is far from the load, it is very hard (if not impossible).

Students can draw what they discover using standard notation:
The lever arm (plank of wood) is drawn as a straight line, and the fulcrum is a triangle under the line in the correct position. Use arrows to show where force is applied (at one end of the see saw - also called the effort), and where the resulting force is felt (under the concrete weight - also called the load).

Ask the students how the height of the ends of the see saw varies as the fulcrum is moved. They can measure the distances for more accurate recording of the results.
Less force over a greater distance (with the fulcrum near to the weight) is an easier way to lift the weight. However, in this case the weight will not move as high.
The amount of work balances: less force over a greater distance (at one end of the lever) balances more force over a smaller distance (at the other end).

In afterschool science, we used the principles of the see saw to move a giant rock.


Turn into a second class lever by taping one end on the ground, lifting the other, and moving the load up and down the plank.

Grades tested: 
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 7
Despina Petrellis
Ebru Montagano
Lindsay Izat
Teaching site: 
Bayview Elementary
Carnarvon Elementary
Eton Arrowsmith Camp
General Gordon Elementary Science Club
ingridscience afterschool
Kerrisdale Elementary
Activity originally developed and delivered: 

Gordon Elementary Science Club