You will need:
- A hammer (make sure that the handle is tapered towards the head of the hammer)
- String
- A ruler
- A desk
- Scissors
Cut about 20 cm of the string with your scissors.
Tie one end of the string tightly around the hammer handle. Make sure that the string can’t slip off the handle.
Tie the other end of the string to your ruler.
Firstly, check that the floor under your table can handle the hammer to fall on it without breaking. You don’t want to break your kitchen tiles or dent a wooden floor!
Resting the hammer handle on towards the tip of the ruler, place the hammer’s head under the desk and the other end of the ruler on the desk surface. Whilst supporting the hammer, slide the string along the ruler until you can feel that the ruler can support the hammer’s weight. Carefully take your hand away from under the hammer and you should find that your contraption balances itself!
Going further
How far can you move the ruler towards the end of the desk? Do you have to adjust the string’s placement? Why?
Get the Unit of Work on Forces here!
- Push, pull
- Friction & spin!
From inertia to centripetal force, this unit covers many concepts about Newton’s Laws!
Includes cross-curricular teaching ideas, student quizzes, a sample marking rubric, scope & sequences & more
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What is going on?
You found the centre of balance!
The weight of the hammer’s head pulled downwards on the ruler end. You would expect that this would make the ruler fall of the table, however that force was transferred back towards the table. As gravity pulls down on the hammer’s head, the handle pushes back upwards on the ruler (you can think of it like a see-saw, where one side goes down and the other side goes up). The string helps this to happen as it acts as fulcrum or pivot point for the hammer to turn on.
By having the majority of the weight of the hammer underneath the table, you were able to balance the hammer as the centre of balance of the whole contraption is under the table rather than off to the side of the table.
Variables to test
- What happens if you use a flexible ruler?
- Can you use different length strings?
- What about different size and shape hammers?
Forces, Friction & Movement
Years K to 6
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School workshop
60 or 90 minutes
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