Balancing the see-saw

Balancing the see-saw

Pencil and paperOnline interactive
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This task is about levers and balance.

Question Change answer

Sam and Terry, decided to sit on a see-saw. Sam is twice the weight of Terry. After some experimentation they sat on the see-saw so that it balanced.
 
a) On the diagram below, draw stick figures to show where Sam and Terry would need to be sitting so that the see-saw would balance. Remember to label the stick figures!

Question 2Change answer

b)  Explain why, with Sam and Terry in these positions, the see-saw will balance.
Task administration: 
This task can be completed with pencil and paper or online.
Level:
5
Curriculum info: 
Science, Knowledge, Physical World
Keywords: 
physics concepts, forces, levers, balance, fulcrums
Description of task: 
Task: Complete a diagram to show where two people will sit on a seesaw to balance it, and explain answer.
Curriculum Links: 
 
Answers/responses: 
   

Y10 (09/1997)
a) Sam must sit half the distance from the centre (fulcrum) than Terry does. easy
b)
As Terry is lighter than Sam he needs to sit further away from the midpoint (or vice versa). To balance the see-saw, the distance of Terry from the fulcrum for Terry needs to be twice that of Sam. (Turning moment of Sam's force must equal the turning moment of Terry's force as shown by the equations and diagram below.)

Therefore

F1 * R1 = F2 * R2
 (Sam)      (Terry)

because

F1 = R2
F2 = R1

 2 correct –
very difficult

1 correct –
easy