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Every time an object moves on earth it is rubbing against something else; another object, the ground, a tabletop, etc. Whenever two objects rub against each other friction happens because objects are not slick. If you look at objects under a microscope they are actually very bumpy. When the microscopic bumps on objects rub together, friction happens and the object that is moving slows down and eventually stops.
Gravity holds objects on the earth and friction keeps objects from sliding all over the place. Zero gravity looks fun when astronauts get to float but zero gravity makes things hard too. What if everything floated? We would be chasing objects all the time. Now think about what life would be like if there was no friction. You could just slide along the sidewalk with no effort at all…but it would be really hard to steer and stop…kind of like roller blades. The wheels on roller blades help reduce your friction so that you can glide across the ground, but as you know, it is tricky to steer and stop.
Do you know how to shuffle playing cards? You hold the card deck in one hand and then use your other hand to pull random numbers of cards off the bottom and put them on the top – an example is the blue card deck on the right. When you pull the cards up, it’s hard – because of friction. All of the cards are rubbing together. However, if you make a bridge, like the red card deck on the left, the cards easily fall back into place in one pile. When you make the bridge the cards bend so that less surface area of the cards is touching each other. Less touching=less friction.
What You Need:
- 2 Thick Books
This experiment will show you just how influential friction can be. Phone books work great for this but any two thick books will do. Place the two books on a table. Push them apart – they slide across the table easily. However, if you overlap some of their pages…it’s not NEARLY as easy.
Open two books and overlap each page of the two books. About half of the page of one book is laying on top of about half of the page of the other book – like your are shuffling playing cards. Now try to pull the two books apart. Can you?
This video will show you just how much strength it takes to pull two phone books apart. Friction is no small force!
- The Guardian: Phone Book Friction Factor
- Physics4Kids: Friction
- BBC School Science Video: Friction
- Sid the Science Kid: Fun With Friction
- Steve Spangler Science: Friction Fire
Here are some books that will help you understand friction and give you some more friction experiment ideas.
- Gizmos and Gadgets Chapter “Get a Grip” about Friction (Pages 28-48).
- Mythbusters Science Fair Book – Is It Possible to Pull Apart Two Phone Books That Are Laid Down With Alternating Pages? (Pages 110-111)
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