Friction - "Invisable Deck"

Standards -NSES Content Standard B -Physical Science: Motions and forces -Grades 9-12

Between any two charged particles, electric force is vastly greater than the gravitational force. Most observable forces such as those exerted by a coiled spring or friction may be traced to electric forces acting between atoms and molecules.

Misconceptions

• Friction is a force like gravity and magnetism

• Friction always hinders motion, thus reducing friction is always desired

• Sliding objects come to a stop because of an absence of applied force

• Friction cannot act in the direction of motion

• Only active agents exert force

• Motion implies active force while no motion implies no force

• Mass makes things stop

• Frictional forces are only due to irregularities in surfaces moving past one another

Magic

There are two specific magic illusions that cause students to focus on friction. The first is “Invisible Deck” (Magicity.com, product number 13-0830, $14.99). In “Invisible Deck,” the magician hands an invisible deck (hence the name) of cards to the volunteer and asks them to shuffle the deck, choose a card, put the card back into the deck, and place the invisible deck on the table. The magician then takes a deck from their pocket, opens the deck and fans through the deck until one card, face down, is found. The card, once revealed, is the same card the volunteer has chosen.

The illusion is very powerful and direct and demands no slight of hand and very little practice. The cards are paired together to equal 13, and diamonds are paired with clubs and hearts with spades. Therefore, if you were looking for the seven of clubs, it would be behind the six of diamonds. The cards are held back to back with a powder that increases the friction between them.

It's not magic, it's science!

This "trick" focuses students' attention on the ideas that friction can be a good thing, its reduction can hinder activities, and that it exists even while objects are not in motion because it is a fundamental property of materials in contact.