How to Do a Friction Science Experiment
Friction is something we experience everyday, but understanding it, let alone explaining it, gets tricky. These experiments will help teach the concept of friction and make it easier for kids to understand.
Test which surfaces create more friction, see how strong friction is, learn how to reduce friction, and even discover the side effects of friction.
Four Types of Friction
- Fluid friction - friction that happens when an object moves through a liquid or gas.
- Sliding friction - friction that occurs when two surfaces slide over each other.
- Rolling friction - friction that is produced when a circular object rolls over another surface.
- Static friction - friction that is applied to an object that isn't moving.
Ok, What Is Friction Anyway?
Most people have a hard time understanding friction because the term is used to describe a force that works in a wide variety of ways.
- Without getting too technical, friction is simply a force that reduces the motion between objects that are in contact with each other. So friction stops or slows down movement.
- In general, the smoother an object, the less friction it will create. The rougher the surface of an object is, the more friction will be produced. The angle of the surface and the weight of the object can also affect friction.
- There are times when more friction is best, like when you are pressing the brakes in a car. And there are times when you want less friction, like when you are going down a water slide.
Now that we have talked about what friction is, let's investigate how it works with the following experiments.
Phone Book Friction Experiment
Stronger Than Glue
Phone Book Friction
- 2 Phone books about the same size (2 books with soft covers will work)
This experiment was tested on the show Mythbusters. The phone books wouldn't come apart using all the Mythbusters' gadgets and even attaching the phone books between two cars. It took two tanks to pull the books apart. That's how strong friction can be.
Phone books are what is usually used for this experiment, but any books with lots of pages (100+) and soft covers will work. Textbooks work great as well. The main thing you want is two books of about equal size.
- Before you begin, just half the books and put them together to show how easily they will come apart that way.
- Now, interlace the pages by alternating a page from each book. The pages of the books will be woven and the spines will be facing out. Make sure several inches of the pages overlap. So you'll lay down the cover of book A, then the cover of book B over it. Then the back page of book A and the back page of book B. Then the next page and so on until the books' pages are woven together.
- You don't actually have to do every page for the experiment to work. You can weave a few pages at a time so it won't be an all day process.
- Now grab one of the book spines and have a friend grab the other spine. Pull on the books to see if you can pull them apart. Have a game of tug of war with the books.
The books will stick together like glue because each page is exerting friction against the page from the other book. When the combined friction from each of the pages is added up, it equals a big force.
Do some tests with interlacing the pages. What if you only weave every ten pages or every twenty? Is the force still as strong? What is the least amount of weaving necessary to produce the glue-like effect?
When you are done with the experiment, just unlace the pages one by one to release the books. They don't have to stay stuck forever!
Which piece will float the best?
Floating Paper Air Fricton
- Two pieces of paper
- Timer (optional)
Air friction (air resistance or drag) is a type of fluid friction. This is a very easy way to show friction in action. The shape of the paper will determine how much friction is caused as it falls.
- Wad one of the pieces of paper into a ball. Leave the other piece of paper like normal. Have someone ready with a timer if you want to make measurements.
- Hold the pieces of paper above your head.
- Drop the pieces at the same time.
The wadded piece will fall to the ground immediately. The flat piece of paper will flutter down more slowly because it has more surface area to create friction or drag on the air as it drops.
You can also try dropping the pieces of papers from a higher spot, like while standing on a table or over a balcony. Does the time difference become more noticeable this way? Try other shapes of paper. What differences do those make? How can you make drop faster? How can you make it drop slower?
Holding Up Rice with Friction
It Floats!Click thumbnail to view full-size
Sticky Rice Friction
- Bottle (about 20 oz size)
- Dry rice
You can't hold up a bottle of rice with a just a chopstick, right? Well, actually you can if you know the trick to friction.
- To begin, fill the bottle with rice. Try sticking the chopstick down into the bottle. When you grab the chopstick and pull up, what happens? The stick should just come right out.
- How do you make the rice stick to the chopstick so you can just pick it up? You've got to add more friction. Here's how: Put the lid on the bottle and tap the bottom of the bottle on a hard surface. Do this a few times to compact the rice and get rid of the air pockets. Now you should have room to add a bit more rice to the bottle.
- Once you've added a bit more rice, stick the chopstick back into the bottle. This time, when you pull up on the chopstick, you should be able to pick up the whole bottle.
- If it still doesn't stick, try tapping the bottom again. You may have to add more rice as well. Sometimes letting the rice settle for about an hour will help if it doesn't seem to be working.
How does it work? Compacting the rice and adding a bit more created more friction when you put the chopstick back in. So the rice had a firmer hold on the stick.
- Slide (or ramp)
- Items to be tested (toy car, shoe, paper, book, ball, block, etc.)
- Water (optional)
You can test how much friction an item will produce by heading to a playground. You could also do this experiment on a ramp.
- Gather some items to be tested. You want a wide range of materials like a toy car, ball, book, shoe with rubber sole, a wooden block.
- Put each item at the top of the slide or ramp and let it fall down on its own. Don't give it a push. Measure how far it went.
- You could try wetting the slide and then retesting the items to see if they went farther than before. You could tape sandpaper to the slide or ramp and see how that affects the distance the items go. Spraying or rubbing oil onto the slide is another good way to test friction.
Which items slide the best? What materials slide the worst? What does this tell you about friction?
Static Friction Experiment
Static Friction Experiment
- Rubber band
- Ruler or measuring tape
- Weight (something to put in the shoe to make it heavier, like rocks)
- Aluminum foil (optional)
- Cooking spray or oil (optional)
This is a good project for older kids who are studying the forces of friction and motion in more depth. It is easy to do, but can teach a lot.
When an object isn't moving, it has static friction. It will take a certain amount of force to get the object moving. The amount of force it will take depends on the surfaces and the weight of the object, among other factors.
To test how much force is needed to overcome static friction, you can try dragging a shoe over various surfaces.
- Cut a rubber band in half.
- Tie one end to a shoe.
- Tug on the other end of the rubber band until the shoe starts moving.
- Measure how far the rubber band had to stretch in order for the shoe to move.
- Now put something in the shoe to make it heavier, like rocks or small pieces of wood. Try pulling the shoe to see how far the rubber band has to stretch before the shoe starts moving.
- Tape some aluminum foil to the ground. Drag the shoe over it and measure the rubber band. Try oiling the aluminum foil. How hard do you need to pull the rubber band now?
- You can also try dragging the shoe over salt or grass or other types of terrain to see how easy or hard it is to get the shoe moving.
- You can even try testing ice. Fill a cookie sheet with water and carefully place it in the freezer for several hours. When it is a solid sheet of ice, try dragging the shoe across it.
What happens if you try a shoe with a different type of sole? What does this tell you about traction and friction?
Can you make fire?Click thumbnail to view full-size
- 2 Sticks
When two objects are rubbed against each other, the friction can produce heat. You can demonstrate this by rubbing two sticks together. This is an old-fashioned way to make a fire.
- Take two sticks and rub them together in a back and forth motion, kind of like sawing.
- Rub as quickly as you can for about 30 seconds to a minute.
- Use your hand to feel where the sticks rubbed against each other. You will be able to feel warmth.
You are probably not going to be able to make fire this way, but you can understand friction from it. The friction will even rub part of the bark off the stick. It's a good way to demonstrate how friction can heat up objects as they come into contact with each other and how friction can wear away objects after a time.
If you really want to make a fire with friction, you can try some of the methods at campfiredude.com.
Salt and Marble Puzzle
Up to the Top!Click thumbnail to view full-size
Reducing Friction with Salt and a Marble
- Test tube with a lid (or an elongated bottle or jar with a lid)
- Marble or gumball
We've tested the friction produced by surfaces and seen ways to increase friction. Well, here is an experiment that reduces friction.
- Put the marble (or gumball) into the bottom of the bottle or tube.
- Fill the tube about 3/4 of the way full with the salt.
- Screw the lid on tightly.
- Try to get the marble to the top of the bottle. Easier said than done, right?
- The trick is all in how you move the bottle. Try shaking the bottle straight up and down. Watch for the marble to work its way to the top.
It works because the friction is reduced when the bottle is shaken. All of the particles are moving around and the marble is free to move.
You can try getting the prizes out of cereal boxes the same way. Shake the box straight up and down until the prize works its way to the top of the box.
What friction experiment are you going to put into motion?
More Friction Experiments
- Learn about friction with moving parts by making ball bearings.
- Find friction lessons and play interactive computer games with friction.
- Test friction in everyday life with these simple activities:
- Hold your hand out the car window when it is moving. How does moving your hand in different positions effect the fluid friction or create drag?
- Try sliding on the floor in socks. Why doesn't sliding on the floor work with most types of shoes?
- Use friction to create static electricity by rubbing a balloon on hair. What other types of materials create static electricity when you rub the ballon on them?
- Erasers work by friction. Get some erasable pens and explore how friction wears away surfaces.
- Head to a playground an slide down the fire pole. Try it with pants on and then with shorts so that your bare legs are against the pole. Why does it make a difference?