ingridscience

Activity video on YouTube.

Stick, clay and styrofoam sculpture
For older students, hand out the materials and challenge them to balance the toothpick on their finger. Show them that it is impossible with just a toothpick, but tell them that they have other materials to add to the toothpick to help them. Give them time to try. If necessary, give them clues that there needs to be most of the mass of their sculpture under the point of the toothpick, and then that the skewers can help to add the mass of the clay low down.
Encourage students to borrow each other's ideas, and that no idea is a bad idea. Encourage students to experiment with various configurations of the materials and see how their new models balance, or not (e.g. what happens if you remove one skewer, what happens if you change the position of the skewers, does it work without the clay at the end of the skewers?...) Tell them to try their sculptures on other things in the classroom.
For younger students show them how to make a simple sculpture: push the toothpick into the styrofoam, then add a skewer with a clay ball, as shown in the second photo. Ask them to try, then modify the sculpture if they like. Encourage students to balance their sculpture on other things in the classroom.

If pushed to one side, the sculpture can right itself.
The sculpture can be rocked back and forth.

Fruit sculpture
Quick to set up.
Try and balance the small end of a grape on your finger. It's pretty much impossible.
Add some mass below the grape, using forks, or other heavy objects, stuck into the grape at an angle.
If the forks are heavy enough an apple will work too.
A banana with a curve can be balanced on your finger if it curves downwards, as the curve puts some mass below the balance point, making it more stable.

Explanation in terms of force and centre of mass
The sculpture balances because the average position of all the mass ("the centre of mass") is underneath the balance point (the point of the toothpick). When gravity exerts a force on this centre of mass, it is pulling underneath the point of the toothpick (not above or to one side of it), therefore the toothpick is stable.
If the sculpture is tipped to one side, gravity pulls the weights back down to the lowest position, bringing the centre of mass below the toothpick once again. As long as the centre of gravity is below the balance point, any sculpture is stable.

Applications of this concept:
Engineers try to design a sports car's centre of gravity as low as possible to make the car handle better.
When high jumpers perform a "Fosbury Flop", they bend their body in such a way that it is possible for the jumper to clear the bar while his or her centre of mass does not.
When balancing on a beam, we stretch out our arms and move them around, to keep our centre of mass over our feet - not as stable as having the centre of mass below our feet, but better than having our arms by our side. Tightrope walkers have a long pole with weights on the end, which lowers their centre of mass, making them more stable.
Astronomical objects in motion are balanced around a centre of mass, forming stable coupled orbits (until a collision or other event moving one of them will make them realign around a new centre of mass).

Sit in the chair.
Hold the cans in outstretched arms, and ask someone to start the chair spinning (or spin it with your feet). It does not need to be going super fast.
Bring your arms inwards, and feel yourself speed up.
Play around to experiment with the forces you are experiencing.

Explanation for younger students:
When the heavy cans change place, the speed of the chair spinning must also change. This is because the amount of force stays the same in the whole system (the chair, you and the cans). With arms outstretched a lot of force is needed to move the mass at the end of your arms, so there is less force to turn the chair. When your arms are pulled in it takes less force to move the weights, so more force can go into spinning the chair and it spins faster.

Explanation for older students:
A rotating object has a constant angular momentum (unless it is acted upon by an outside twisting force).
Angular momentum is the product of mass, the distance to the centre of the circle (radius), and angular velocity = vmr
When the mass is far from the centre of the circle, r is larger.
When the mass moves inwards, r gets smaller. As the mass is the same, the velocity must increase to keep the angular momentum the same.

Discussion on sports: this phenomenon is why an ice skater or a dancer doing a pirouette draw their arms and legs in to spin faster. Also used by divers or gymnasts when they go into a tuck position to flip or twist at a faster rate.

Adapted from the Exploratorium snack https://www.exploratorium.edu/snacks/strange-attractor

Lay the 3 identical magnets in a triangle under the support.
Hang the hole magnet so it is suspended between these 3 magnets, and is attracted to them, but does not touch them.
Gently swing the suspended magnet so that it moves irratically between the other 3 magnets.
Adjust the height and position of the suspended magnet, and the positions of the other 2 magnets until you get best results - the suspended magnet can swing for quite a while before it finds a stable position.

Show all the students the different cards and demonstrate and practice the noise for each one.
Whale sounds can be found online, though note that often the sounds are played faster so that we can hear them e.g. http://www.nefsc.noaa.gov/psb/acoustics/sounds.html (This site indicates how much the sound is changed). The humpback and blue whale are the classic whale sounds.

Play one round with all students blue whales. They can hear each other's noises and respond to each other.
Then distribute all cards, and ask blue whales to find each other, with all the other noises going on - it is much harder.

This is what whales face with the increased noise pollution from man, along with the noise pollution already there from other natural phenomena e.g. ice cracking in their environment.