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| http://www.ingridscience.ca/node/21 |
Materials:
For each catapult:
- foam core/very stiff cardboard in a square U shape - see notes on cardboard
- elastic band, #32 works well
- plastic spoon
- small piece of coffee stirrer stick
- piece of aluminum foil
- optional: masking tape to mark firing line
Procedure:
We will build a simple toy that works with the forces we have been talking about.
Students each build a simple catapult. (Stretch the elastic band over the arms of the foam core. Use the piece of stick to twist up the rubber band, then slide the spoon in, orienting it so that it acts as the arm of the catapult).
Once everyone is done, tell them the task: while staying behind a line, fire balls of tin foil as far as you can. What sized balls go the furthest?
After 5 mins, ask what they changed to make the balls go further. (Direction of the force, strength of the force by pulling the spoon back more or less, weight/size of the object being fired, strength of the force by twisting the rubber band more or less).
Then more time to try out other students’ suggestions. Ask them to think about the forces on the paper ball.
Discussion on the forces involved in each stage of the catapult firing (force from hand to pull back the spoon, force in the elastic band (potential energy), force as the elastic band unwinds and moves the spoon, force of the spoon on the foil ball, gravity pulling the foil ball to the ground).
Students each build a simple catapult. (Stretch the elastic band over the arms of the foam core. Use the piece of stick to twist up the rubber band, then slide the spoon in, orienting it so that it acts as the arm of the catapult).
Once everyone is done, tell them the task: while staying behind a line, fire balls of tin foil as far as you can. What sized balls go the furthest?
After 5 mins, ask what they changed to make the balls go further. (Direction of the force, strength of the force by pulling the spoon back more or less, weight/size of the object being fired, strength of the force by twisting the rubber band more or less).
Then more time to try out other students’ suggestions. Ask them to think about the forces on the paper ball.
Discussion on the forces involved in each stage of the catapult firing (force from hand to pull back the spoon, force in the elastic band (potential energy), force as the elastic band unwinds and moves the spoon, force of the spoon on the foil ball, gravity pulling the foil ball to the ground).
Students can measure and record on a graph how far their ammuntion goes.
