Challenge your students to put a penny in a cup without touching it.

The solution is to use inertia to your advantage by taking the playing card out of the way as quickly as possible.

This is a simple (and less costly!) way to practice the "waiter's trick" of pulling a tablecloth out from under a plate. This is a demonstration they can easily recreate at home without breaking all of the dishes!

A full explanation of the physics involved is included in the Pull the Tablecloth resource.

### Objectives

• Describe a scenario that demonstrates the property of inertia.

### Materials

• Per student or small group:
a cup
a penny
playing or index card (stiff paper)

### Key Questions

• Before the demonstration is performed, what forces are acting on the cup?
• Before the demonstration is performed, what forces are acting on the card?
• When you flick the card, what forces are acting on the penny?
• Does this trick work with a lighter object (like a cotton ball)? Why or why not? Experiment and see how light an object can be for the trick to work.

### What To Do

1. Have students set up a playing card over the mouth of a cup, and place a penny on top, directly over the centre of the cup.
2. Challenge them to figure out how to get the penny in the cup without touching the penny or lifting the card.
3. Once they have found the solution, have them try with a stack of pennies. How many pennies can they drop into the cup at once?

• Solution: Students should flick the card swiftly with their finger, to send it out from under the penny, allowing it to drop into the cup.

Survivors

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Egg BB

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Geodessy

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.