Is it magic or is it gravity?
Image: Kagen McLeod
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Gravity's Engines
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Key concepts
Gravity
Friction
Inertia (Newton's First Law of Motion)
From National Science Education Standards: Position and motion of objects
Introduction
Have you ever seen a magician sweep a tablecloth quickly off a table and leave all the plates and glasses still in place? The trick isn't magic at all—it's science! And you can use the same principle (without breaking any plates) to make a coin fall into a small container.
A coin resting on a countertop isn't likely to do much—unless you or someone else does something to move it. If you give it a gentle push, which way does it go? What about if you drop it from the height of a few inches? The coin is acting the way most solid objects do—it stays at rest until you do something to it. But can you make something go where you want it to while it's at rest? Look like a magician by making a coin fall from its balancing point on top of a paper loop into a small container—with little more than gravity helping you out.
Background
The key to the famous tablecloth trick is also crucial to make this activity work: speed. By using one swift, smooth motion, you are overcoming the resistance of friction (the slight grip) that occurs between the paper and the coin. The quick move gives gravity a chance to overpower the friction—and demonstrate inertia.
Inertia, explained by Sir Isaac Newton and now known as Newton's First Law of Motion, says that an object at rest will stay at rest (and an object in motion will remain in motion) until acted on by another force, such as gravity—or you!
Materials
• Coin
• Bottle, jar or canister with a small top opening (larger—but not too much bigger—than the coin)
• 3- by-5-inch note card or other sturdy piece of paper
• Scissors
• Tape
• Pen or pencil
• Water (optional)
Preparation
• Carefully cut the index card lengthwise into a strip about 3/4 inch wide.
• Tape the card’s ends together and shape it into a ring that will balance on top of the container's small opening.
• Fill the container part of the way up with water if your container is not heavy enough to be stable on its own—or if you just want to see your coin make a splash!
• Balance the paper loop with the broad side on top of the container's opening so that the ring's open center is facing you.
• Balance the coin on the very top of the loop—directly above the container's opening. This balancing might take a few tries, and if it is too difficult, try using a larger piece of cardstock to make a bigger loop.
Procedure
• Can you get the coin into the container without using your hands?
• Place the pen or pencil horizontally inside the loop. Slowly pull the loop off the top of the container. What happened to the coin?
• Set the loop and coin back up on top of the container.
• Now try a fast motion: insert the pen or pencil into the center of the loop and quickly pull the loop to the side (be careful with the sharp tip of the pen or pencil). Where did the coin go this time? Did it fall closer to—or inside—the container?
• If the coin didn't fall into the container, observe how much closer it came than the slow push, and try it a few more times.
• What is the slowest you can pull the loop away and still have the coin fall into the container?
• Extra: What happens when you use a bigger or smaller paper loop?
• Extra: Try turning this into a version of the magician's tablecloth trick. Place a flat index card over the opening of the bottle. Place a coin on top of the index card so that it is directly over the opening. As fast as you can, try sliding the index card away. Can you get the coin to fall into the opening below?
Read on for observations, results and more resources.
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10 Comments
Add Comment"Have you ever seen a magician sweep a tablecloth quickly off a table and leave all the plates and glasses still in place? The trick isn't magic at all—it's science!"
Reply | Report Abuse | Link to thisOf course it is not science. Science may well try and explain it but it simply reality.
Isn't science "real"??? And if it is not science, what "un-scientific" (but "real") explanation(s) would you propose?
Reply | Report Abuse | Link to this"The quick move gives gravity a chance to overpower the friction—and demonstrate inertia."
Reply | Report Abuse | Link to thisReally? Do you read your own stuff?
Sorry, but gravity is too weak to "overpower" friction and demonstrate inertia in this case. Gravity's pull on a table cloth is enormously weak. What is being demonstrated is the difference between a strong (or weak) lateral force (the pull on the cloth), and the sliding coefficient of friction between the table cloth and; the plates, glasses and silverware. The lateral force must be very large compared to the friction, in order to work.
Reply | Report Abuse | Link to thisYou're both right. Since science is the study of what's real, it is both reality and science.
Reply | Report Abuse | Link to thisSimple, gravity and therefore the weight of the coin hugs
Reply | Report Abuse | Link to thisthe table cloth. Friction comes to play only when we pull on the table cloth. The friction force acting on the coin starts it to move across the table. But the table cloth is yanked so fast away from the coin the coins inertia cannot be overcome that fast, leaving the coin behind.
DURGADAS DATTA published a paper in ASTRONOMY.NET in year 2002 which has given a direction to new thinking to understand DARK ENERGY and DARK MATTER. The paper is--MISJUDGEMENTS BY NEWTON AND EINSTEIN. We live in a matter universe surrounded by antimatter universe on opposite entropy path. The common boundary is violent due to annihilation of matter and antimatter. GRAVITOETHERTONS or five god particles are produced and injected into our universe as DARK MATTER AND DARK ENERGY. EARLIER DAYS WE USED TO CALL IT ETHER. But our universe is non uniform field density of gravitoethertons soup and as such NEWTONS LAW WILL BE ...F=P.G.M.m/R.R WHERE P IS PERMEABILITY OF THIS SOUP. IN THIS NON UNIFORM UNIVERSE ,NEITHER NEWTON NOR EINSTEIN IS CORRECT. The five GOD PARTICLES are --four for four fundamental forces and one for mass creation. GRAVITY IS THE EFFECT OF MONOMAGNETIC COUPLING EFFECT OF GRAVITON--THE GRAVITY FORCE PARTICLE . So gravity is a push not pull. WE SEE CENTER OF EARTH / CENTER OF GALAXY ALL VERY HOT OR BLACKHOLE DUE TO FOCUS OF GRAVITOETHERTONS. DUE to monomagnetic coupling ,the earth , stars,galaxy ..all magnetic and we also live in magnetic universe. But we do not exactly see these god particles except their effect --gravity etc etc. SOON LHC AT GENEVA will/ may see these force particles . Our solar system may prove NEWTON AND EINSTEIN CORRECT but larger universe is where we will observe all laws and constants varying due to this non uniform universe and we have to be careful. I suggest NASA and LHC,CERN should jointly look into a different physics and try to develop string theory on spherical coordinates taking time as non dimensional. BALLOON INSIDE BALLOON THEORY OF MATTER AND ANTIMATTER UNIVERSE ON OPPOSITE ENTROPY ALSO SUGGESTS--that one universe will reach a tends to zero entropy and a big bounce will occur --again two universes on CP VIOLATION. Again matter universe will form on seeds of remaining big black holes escaped full evaporation to give a universe by chance tuned to laws for formation of lfe and again we will come back to ponder about universe--may be many many billion years after as this re cyclic is again and again for eternity. THIS IS THE ACTUAL RE CYCLIC MODEL NOT AS DESCRIBED BY DR.ROGER PENROSE. SO READ THE THEORIES OF DURGADAS DATTA TO UNDERSTAND PRESENT DAY ACCELERATING COSMOS WITH DARK ENERGY--MATTER--FLOW ETC ETC.
Reply | Report Abuse | Link to thisdebu got all of that from an elementary school demonstration of Newton's 1st Law of Motion? I can only imagine what debu might come up with if he or she were allowed to watch the Big Bang Theory on CBS on Thursday evenings.
Reply | Report Abuse | Link to thisThere seems to be a general misunderstand of what I was trying to say. Let me try again.
Reply | Report Abuse | Link to thisScience is a methodology which is used to make sense of reality. When we say something happened in a particular way because it is scientific then we are getting things in the wrong order.
So events happen and science attempts to understand it. Now the other way which is to say science made that happen that way which is clearly incorrect.
Indeed the scientific method is really all about being sceptical of itself.
o Use your experience
o Form a conjecture
o Deduce a prediction from that conjecture
o Test it.
So it understands doubt and we can never say that science understands something. At best we can say we have not found a test to make us doubt the given conjecture.
Matt knows better from a higher elementary laws of motion.We expect him to share some thoughts on gravity.
Reply | Report Abuse | Link to this