Lesson Four: Friction
Did you ever notice that it is much easier to ride your bike down a smooth hill than a bumpy one? In both scenarios, gravity is the force pulling you down the hill. But what is the force that is slowing you down? Friction! Friction is the force that slows or stops moving objects. Friction occurs when objects rub up against one another.
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Activity: Put the palms of your hands together and rub back and forth for 20 seconds. How do you palms feel? The friction in your hands is causing them to feel heated. Now, put lotion on your palms and rub together for 20 seconds. How do your palms feel this time? Was it easier to move them back and forth this time? The lotion acts as a lubricant, reducing the friction between your hands and therefore, making it easier to move them.
Watch this friction investigation. Here you will see how objects move differently over different surfaces. Which surfaces have the least amount of friction? The most?
Now, try it for yourself. Click on the link below and follow the site’s instructions in order to see how a car travels over various surfaces, each with a different amount of friction.
What did you notice about each surface? Which was the car able to travel over fastest? Slowest? What caused the variation of speed?
Although it causes things to slow down or stop, friction isn’t always a bad thing. We need friction to keep our car tires from sliding all over the road and our feet firmly on the sidewalk. Just the same, friction can cause things to not work properly, say in a car’s engine. Sometimes we need to reduce friction to keep everything running smoothly. Read the four pages of the site linked below. While you read, think about how friction can be both advantageous and unfavorable.
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Game time! It's a race - use your knowledge of friction to get MI High's Carrie to the Invigatron before Beryl 'The Beefcake' Bagshot steals it! Follow the directions on the site listed below to play the interactive friction. (*Note: it takes about 30 seconds to load. When it says 2 of 2 complete, drag your mouse over the green screen and click “play”. )
Try this interactive activity! Test the variations of a traveling cart when different amounts of mass, friction, and acceleration are applied to it by adjusting the newtons and objects being carried on the cart. You may also try the "Net Force" activity where you choose the amount of people on each side of a tug-of-war to see how force impacts this classic game.
*Note: Newton - the unit of force that is of such size that under its influence a body whose mass is one kilogram would experience an acceleration of one meter per second per second
Now that we have learned all about friction, let’s test our knowledge. Click on the link below to take an online quiz. Be sure to click “Check Score” at the end to see how well you understand our newest force, friction!