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Tower of Coins

Sent in by:
Layne and Sam of Suffolk, VA

TIMBER! Can you keep a stack of nickels from toppling?

## Materials Needed

• 12 nickels
• 12 pennies
• 12 large washers
• 12 checkers
• flat metal spatula
• rubber spatula
• fork
• butter knife
• table

## Instructions

1. Stack the 12 nickels on a table.
2. Try to get the bottom nickel out of the stack without making the tower of nickels tip over.
3. You can use a flat metal spatula, a rubber spatula, a fork, or a butter knife to help you do it.
4. After some practice, you'll see that if you use just the right amount of force, you can always push the bottom nickel out!
5. Here's why this works. Take a look at the stack of nickels -- they are at rest, or not moving. Objects at rest don't move unless you push or pull them. So, to make the bottom coin move, you need to push or pull it. To make it move without knocking over the whole stack, you need to push or pull quickly. Why? Because of friction. Friction is a "sticky" force that appears when two objects (like coins) rub against each other. If you push the bottom nickel slowly, friction helps pull the stack along with it by "sticking" the coins together. If you push the bottom nickel quickly, the coins still rub, but the friction force doesn't have time to get the stack moving. So, the coin shoots out without pulling the stack with it.

Now it's time for you to experiment. What happens if you stack other objects like checkers, washers, or pennies? Or what happens if you stack more than 12 nickels? Try using other tools, such as a playing card or a ruler, to remove the bottom object. Choose one thing to change (that's the variable), and predict what you think will happen. Try it out and then share your results with the world in our fabulous ZOOMsci feedback area.

Jioko, age 14 of TX wrote:
it never fell untill 2 hours

Julie, age 9 of San Jose, CA wrote:
It was 25 inchs but it still holds

Mackenzie, age 10 of Cleveland, OH wrote:
I need more nickles.

Joan, age 14 of Yardley, PA wrote:
It was a great experiment! The coins stayed where they where and it was a great way to demonstrate inertia!

Sierra, age 13 of Cantin, CO wrote:
i got 80 coins thay fell down.

Katie, age 12 of Crowley, LA wrote:
the coins went up to almost a foot it was amazing but you have to be very steady

Taylor, age 8 of Kingsport, TN wrote:
They really did'nt fall down I just kept stacking!

Max, age 8 of Vancouver, WA wrote:
i counted each coin so I know the exact number of coins I stacked. I stacked50 nikels on top of each other it was cool but it woud've been more cool if you guys where there.

Jocelyn, age 10 of New York, NY wrote:
when I did the tower of coins it was cool but it took me half an hour just to do 50 coins in one tower but arter a while my brother knocked it down.

Sierra, age 8 of Stanton, CA wrote:
It did not fall for 84 hours!

Cassandra, age 10 of Clair, NB wrote:
Stacking coins Isinte as easy as it looks they falls over the side of the table and you lose them but for me it works out well

Tess, age 8 of Patrica, AB wrote:
When I made the tower of coins I made it 15 inches hi I put 2 more on I tried to catch it from falling and I put 1 more on and then it came falling down and I tried to make a new one higher and it fell down at the same size.

Tynisha, age 13 of Philadelphia, PA wrote:
When I did it they fell, and after they fell I put them back up, and they stayed I was so excited/shoked that they stayed up!!

Ellana & Raven, age 8 of Dublin, CA wrote:
Me and my sister, we made a tower of coins but sooner my cat rocco he knocked it down so we strated to laugh but we did it again.

Abigail, age 12 of Fond Du Lac, WI wrote:
The butter knife worked really well. We took a while to get the hang of it but eventually the phemoneon worked!!!

Kaley, age 8 of Winnipeg, MB wrote:
I did this with 21 pennies. It was hard but I did it with the butter knife. The force slowly pushed it out. It was so fun!

Brandi, age 14 of Rio Rancho, NM wrote:
When I did this I used 20 pennies and a knife I got through all of them without spilling any and after that I tried a fork but that didnt work for me they all fell.

Ari, age 6 of Marietta, GA wrote:
The fork worked and the flat spatula worked on quarters and nickels, this was super cool.

Dipika, age 8 of Highlands Ranch, CO wrote:
To cool! I tried it with nickels and a metal spatula, it worked. Way coool!

Valerie, age 10 of Florida wrote:
The ones that did not fall were the checkers with the fork and metal spatula.

Cody, age 10 of Newton Falls, OH wrote:
First I used a spatula to try to move a coin, and it did not work. Then I used a card to move a coin and it worked perfectly. I also tried to use checkers, but they were too light. You have to go very quickly to make this experiment work.

Jeremy, age 10 of Leavittsburg, OH wrote:
I first tried using a spatula to push the bottom coin and it failed. Then I used a card and it worked. Then I tried the spatula again and it worked. I noticed you had to push really hard. I also tried checkers too. They were too light.

Maggi, age 10 of Braville, OH wrote:
It was really, really hard! Mine fell down alot we even tried checkers. It didn't work! Then we used playing cards to knock down the tower.

Carissa, age 11 of El Cajon, CA wrote:
With the fork they all fell over. I think the fork was too thick. One of the spatulas were too thick, but the other got the bottom one out the 5th time. The BEST one, though, was the butter knife. I hit the bottom one with the side of the knife and it shot out and it was like nothing happened!

David, age 9 of St. Joesph, MO wrote:
I used 17 pennies, and I used a plastic spatula. At first I could get the two bottom pennies and then I got the bottom one.

Rina, age 8 of Elkins Park, PA wrote:
The points on the fork it helped the coins not to fall. With the midium and big size spatula the coins fell down. With the small and rubber spatula the coins stayed up.

Kyle, age 6 of Superior, CO wrote:
At first, the stack fell down because we pushed too slowly. Then we pushed faster and the bottom coin came out. (Evan got 3 coins to come out).

Dominique, age 8 of Vernon, CT wrote:
The first time I did it penny, nickel, dime, quarter ect. until I got to 12 then I tried largest to smallest and it worked. It almost fell on the 1st nickel.

not yet implemented