ingridscience

Draw/write something on the piece of paper.

Place the drawing behind the card so that it is not visible.
Find the place to hold the mirror so that you can see around the card at your drawing.

Stick the drawing on the underside of a table.
Find the place to hold the mirror so that you can see under the desk at your drawing.

Play around with other ways of using the mirror to see around corners/behind you etc.

To make the catapult arm:
Tape the short popsicle stick to the spoon handle, to reinforce it.
Lay the end of the spoon handle over a silver handle of the binder clip, and temporarily open up the binder clip, so you can tape them together tightly with duct tape.
Use a small loop of tape to secure the min cup cake holder in the scoop of the spoon - this makes a deeper bucket for the ammunition.

To attach the catapult arm:
Clip the spoon handle with its binder clip to one lip of the tin can, so that the catapult arm can swing up to the other side of the can.
Attach the second binder clip to the other side and the other end of the can.
Loop an elastic band over the scoop of the spoon, across the can, and behind the inside handle of the second binder clip. The catapult arm should be pulled up against the rim of the can.
One of each of the binder clip handles can be flipped back, to make the attachment more secure.

To fire the catapult:
Make ammunition from balls of aluminium foil.
Load the ammo in the bucket, while tilting the catapult backwards, so the ammo doesn't fall out.
Pull back the arm of the catapult by the reinforced handle, while moving the can back to its horizontal position.
Let the arm go. The ammunition should fly several metres.
(In the classroom students can fire the catapult without any ammunition, to understand how it works.)

Discuss the forces and energy transfers:
When you pull the arm back, energy is stored in the elastic band. As the arm is released, the elastic band contracts again, exerting a force on the catapult arm and pulling it forward again. The bucket of the catapult exerts a force on the ammunition, pushing it forward with it. When the arm hits the can, the ammunition has no force to stop it from moving, so it continues to project forward. Gravity pulls the ammo downwards as it moves, so it makes an arc across the room.
The catapult is a class 3 lever, with the effort (the elastic band pulling on the catapult arm) between the fulcrum (the binder clip hinge) and the load (the bucket). The bucket moves further than the spoon handle, but experiences less force at one time (though has plenty of force to move the ammo forward).

Discuss Newton's Laws in the catapult:
1st Law: Focus on the ammo - catapult arm makes it move. Gravity makes it fall. Air slows it down. The ground pushing up makes it stop.
2nd Law: F=ma. A greater force (stronger band/pulled back more) will make it go further. A larger mass will go less far.
3rd Law: At each step there is a force pushing back on the ammo, even when it is still. When one force is greater than the other, the ammo moves or slows down.

Take the students outside to fire their catapults.
Scrape out lines in a gravel field or chalk up concrete, to provide the students with metre marks from a firing line. Students can stand on the line and measure how far their ammo flies each time.

Change the forces:
Ask students how they can make their catapult fire further (also helps students that are having trouble). Ideas: make the elastic band stronger by doubling it up, or switch for a stronger elastic band. I use three elastic sizes, #32 to start with, then add in #16 and #64. The sizes do not matter, but these bands do work.

Graph the results:
Ask students to record their distances for each sized ammunition.
Graph the data, with students initialling their places on the graph (see photo).
Note that I have not been able to make any consistent pattern from graphing whole class distances, either from different sized balls or different elastic bands. Neither is there no clear correlation between the distances fired and different elastics when used by the same student with only a few data points.
It is still OK to graph and see that there is no distinct pattern - opportunity to ask what other variables there might be, and how to test for these. Also an opportunity to explain that sometimes we need more data to see if there are any patterns. I want to try students each graphing their own data - and collecting around 10 data points each. (I think they will also more naturally want to collect more data to find a pattern.)

Introduction:
I have seen this called a "viking catapult", based on how it is made up of rods lashed together.
The skewers model tree trunks, the elastic band models rope and animal sinews.

Procedure:
Clip the sharp tips off the bamboo skewers. Cut one of the skewers in half.

Refer to the image to see the final shape of the scaffold, and follow this order of construction if you like:
Use an elastic band to secure three skewers together at one end.
Use another elastic band to secure the other end of one of these skewers to two more skewers (at their end).
Take one free skewer end from each bundle, and bind them together - this should make a triangle.
Take the last free skewer end from each bundle, and bind them together - this should make a second triangle. The two triangles you just made have one skewer in common.
Hold the two triangles apart from each other and brace them open with the two short skewers, using elastic bands at each joint, as in the photo.

To make the ammunition pouch:
Loop an elastic band through each of the holes.
Two of these elastic bands can hook over the upright struts of the catapult.
The third elastic band should be secured to the bottom skewer with one or two half hitches.

Make ammunition from balls of aluminium foil.
Hold the ammo in the pouch as shown in the second photo, then release. It should go several metres.

Show students how to read their thermometer, making sure not to cover their hand over the bulb.
Students make temperature measurements at different places in the pond. They record each temperature measurement on correct location on the map.

Discussion: was there a change in the pond temperature?
We found the shady spots were a little lower in temperature.

Using a paint stick (good for lower primaries)
The fulcrum can be a pencil or short dowel. Find the balance point for different sized balls of play dough on each end. Younger students can add in lego or other classroom objects. Give a set of challenges (see photo) and/or Encourage investigation with questions: How does moving the fulcrum change how they balance? Can a small ball lift a large ball? How small can a small ball be to do this? Where does the fulcrum have to be to make them balance each other?
Discuss the pushes and pulls that keep it balanced: gravity pulls on the weights, to make them push down on the stick. When the pushes on each side of the balance point are equal, the stick will balance.

Using a ruler, and adding measuring
The same activity as with the paint stick can be conducted with a ruler, and the markings used to record how far a mass is from the centre and how this affects the balance point. Graph the results and the points should make a straight line (though data will be more messy than this). To graph the data from multiple students on one graph, make sure they have the same sized play dough.

More free exploration
Students can also use paint sticks and be given additional materials to try lever free experimentation, for some less structured exploration of levers and balancing, probably best done after these more structured activities, to ensure some focus.

Using a long stick
More dramatic, but more chaotic with many long sticks in use.

Balance the stick on one finger.
The balance point should be half way along.
This is because the mass of the stick is the same on each side, so gravity pulls down on each side with equal force. As the stick is an even width, the balance point will be in the centre.

A trick to find the balance point of any stick:
Start with the stick resting on a finger at each end, then slowly slide the fingers together along the underside of the stick. The rod will slide over the fingers, then stop moving over them, in turn, as the weight on each finger changes. The fingers will end up meeting at the balance point in the middle of the stick. See http://www.exploratorium.edu/snacks/center-gravity

Now add some play dough to one end of the stick, and find the new balance point.
It should be nearer the weight.

Now experiment with adding different sizes of play dough to different places along the stick.
The balance point will move depending on the relative weights and their positions out on the stick.
The lighter weights need a longer length of stick to balance a heavier weight. The further out the mass is, the greater force it exerts (actually torque as the force is exerted on a rotating lever arm). The mass has more of an effect when it is further away (the torque is greater).
Students can draw what they find in each case (see photo and attached worksheet).