# Mechanics

## Sand Lever

As you pull down on the rope a force is applied downward that lifts the sandbag on the other end of the lever. This downward force is called Torque. As you apply torque at a further distance from the fulcrum, it becomes easier to lift the bag of sand.

## Hula Hoops

Hula hooping is a perfect example of balancing different forces in nature by simply using a person’s body. A person is able to keep a hula hoop spinning around the waist by applying an upward force and a turning force (torque), maintaining the centripetal force of the hoop.

## Coriolis Carousel

The two riders sit on the apparatus that is rotated about its center. Since they are in a rotating reference frame, when they try to throw balls at each other, the balls are deflected due to the Coriolis force.

## Lazy-susan & Hand Weights

This classic demonstration of angular momentum needs only a rotating stool and two hand weights. Start by spinning on the stool with the weights far from the axis of rotation, giving you a large moment of inertia. As you bring the weights closer to the axis of rotation, your moment of inertia decreases. By conservation […]

## Galileo’s feather and coin

Intuitively we know that if we drop a feather and a coin from the same height, the coin will reach the ground first. However, this is due to the difference in air resistance between the feather and coin. When placing these items in a vacuum, removing the air, we see that the feather and coin […]

## Egg Roll

When rolling a hardboiled egg and an uncooked egg down a slope, the raw one will reach the bottom first. This is because the hardboiled egg requires a lot of rotational energy as the shell, egg white, and yolk need to be set in rotation. On the other hand, only the shell of the uncooked […]

## Downhill race with cookie cans

One of the cookie cans has weights around the edge while the other has weights concentrated in the center. The one with weights around the edge have a high moment of inertia and therefor resistant to turning quickly resulting in the cookie can with the weights in the center to win.

## Balancing Forks (WITH SKYHOOKS)

By positioning forks together such that their center of mass is at just the right spot between them, they can balance on a toothpick with ease.

## Balancing bird (center of gravity)

Because of the way that the balancing bird is spreading its wings, it is able to distribute its weight in such a way that it creates a center of gravity right below the beak. Having the center of gravity below the beak allows the bird to be balanced on a finger.

## Bed of nails

A person can be able to sit on a bed of nails without being injured. This is because the pressure that the nails create is inversely proportional to the area in which a force is spread along.

## Nose basher with croquet ball

Through the conservation of energy, once the croquet ball is released at a certain height the potential energy is converted to a combination of kinetic and potential energy. As long as no additional velocity was added to the system in the beginning, the ball should return at the same point at the end of it’s […]

## Moment of inertia rods

Objects with a higher moment of inertia resist the change in angular velocity. A comparison can be felt when rotating a rod with weight in the center on weights around the edges. Weights around the edges result in a high moment of inertia and therefore harder to turn.

## Brazil Nut Effect (WITH SKYHOOKS)

Granular material of varying sizes, like sand with nuts in it, are all placed in a container the center of mass of the system is likely not at the lowest point. When the container is disturbed from shaking the larger particles like the nuts tend to be displaced towards the top so that most of […]

## Phonebook Friction

If the pages of two phonebooks are stacked with one another connecting the two books, it becomes seemingly impossible to pull the books apart. The harder you try to pull the two books apart, the harder the stacked pages in the middle are squished together, increasing the normal force and thus the overall force of […]

## Elliptical Pool Table

Given a pool table in the shape of an ellipse with a single pocket placed at one of the ellipse’s foci, the cue ball will always go directly into the pocket, no matter the direction it is hit in, so long as it is hit from the other focus.

## Hoberman Angular momentum

Once the sphere is set in motion, it has a fixed angular momentum. Pulling the string makes the sphere smaller so that it’s moment of inertia decreases. Since angular momentum is conserved, its angular velocity increases to compensate.

## Galilean cannon

When dropping a singular ball, it can be seen that it does go as high as it was dropped from. When stacking them however, once they all hit the ground, the linear momentum of the bottom ball transfer to the next ball and continues until all the linear momentum of the system is in the […]

## Magic Bubbles

This demonstration is simply an empty aquarium filled with dry ice. With time the dry ice will sublimate into gaseous CO2, which is denser than air, that fills the aquarium. Blowing bubbles into the aquarium, you can see that the bubbles will float due to the buoyant force of the dense CO2 gas giving the […]