Toy Fish That Swims in Water Updated

Toy Fish That Swims in Water

Make a Newspaper Fish Swim with Surface Tension

A pond science projection

Make a Paper Fish Swim with Surface Tension — Can you make a toy fish that swims along--with physics? Try this high-tension activity and find out! Credit: George Retseck

Cardinal concepts
Physics
Forces
Molecules
Surface tension

Introduction
Have you lot ever wondered how water droplets form on a window on a rainy day, why some bugs can walk on water or why you lot employ soap to wash your hands? All of these things are related to the phenomenon called surface tension. In this activeness y'all will learn how you can apply surface tension to make a fish cutting from a slice of paper seem to swim around on its own!

Background
Whether riding in a auto on a rainy solar day or spilling water on the kitchen counter, you take probably seen water droplets form. What holds these water aerosol together—sometimes in nearly spherical shapes? Why don't they spread out evenly or fall apart into even smaller drops? They are held together by something called surface tension. Water molecules are slightly attracted to one another; at the surface of a water droplet, they are more than attracted to the other molecules around them than to the air higher up. This forms a thin "pare" of strongly attracted water molecules that are difficult to break through.

Sometimes loftier surface tension tin exist beneficial—such equally for insects that walk on water. Other times nosotros want to lower water's surface tension—for instance, when we are doing laundry or washing dishes. This is considering there are lots of tiny holes in between pieces of dirt or vesture fabric, and high surface tension tin can make it hard for h2o to seep into those holes. Calculation lather or detergent decreases h2o'southward surface tension, making it easier to penetrate all those lilliputian nooks and crannies. Exercise y'all think you can brand apply of this change in surface tension to make an object skim across the surface of the water? Effort this project to observe out!

Materials

Shallow tray
Tap water
Slice of paper
Scissors
Medicine dropper
Soap
Workspace that can tolerate soapy h2o spills

Preparation

Cut out a pocket-size "fish" shape from your piece of paper. Brand sure the fish has a 5-shaped notch in its tail.
Make full your shallow tray partially with h2o and bring information technology to your workspace.

Procedure

Carefully identify the paper fish on the surface of the water at one finish of the tray with its tail facing outward and its head facing into the tray. Brand sure the fish floats and you do not button it underwater.
Use the medicine dropper to carefully place a single drop of soap on the water in the 5-shaped notch of the fish's tail. What happens?
Empty, rinse and dry the tray; cut out a new newspaper fish and endeavour over again. Exercise y'all get the same result?
Endeavor reusing i of the paper fish with fresh water, reusing the tray of water with a new paper fish or both. Tin you get it to work a second fourth dimension? Why or why not?
Extra: Attempt cutting out and testing some unlike shapes. Practice the shapes accept to be "streamlined" like a fish? What if the shape is symmetric like a circumvolve or blocky like a square?
Actress: Attempt the activity with dissimilar liquids you have in your kitchen, such as vegetable oil or juice. Practise any liquids have the same outcome as soap? Practise any of them not piece of work? Why practice you recall this happens?

Observations and results
When yous identify the newspaper fish on the h2o's surface and information technology floats, the surface tension of the water pulls at information technology from all sides. Because it is completely surrounded past water, surface tension pulls evenly in every management, and information technology does not motility. When y'all add a drib of soap to one side of the fish, the surface tension on that side suddenly becomes lower so the fish is non pulled as hard in that direction, and it moves in the other direction. This is a keen instance of Newton'south first law of movement! The fish is initially at rest and the forces on it are counterbalanced so it remains at rest. When yous add the soap, the forces on it become unbalanced so it accelerates.

You will probably detect it is difficult to either reuse a paper fish or a tray of water. Once the fish and/or water are "contaminated" with some lather, the soap spreads and the surface tension is lowered everywhere, rather than on just one side of the fish, so y'all can no longer make information technology movement. You can probably notice, nevertheless, the effect does work with many other shapes—fifty-fifty squares! Yous might also observe that other liquids, such equally oils (which accept a lower surface tension than water) work just as well as lather, merely liquids such equally juices (which are mostly water) do not.

Cleanup
Clean up any spilled liquids.

More to explore
Surface Tension, from Hyperphysics
Build a Raft Powered by Surface Tension, from Science Buddies
Measure Surface Tension with a Penny, from Scientific American
Scientific discipline Activities for All Ages!, from Scientific discipline Buddies

Nigh THE AUTHOR(S)

Ben Finio is a senior staff scientist at Science Buddies and a lecturer at the Cornell Academy Sibley School of Mechanical and Aerospace Technology. Follow him on Twitter @BenFinio.