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| *Vultures Knob>>>Street Bike |
Science--Motion and Friction..Help!? |
On a level street why does it take more force to start the bike moving than it does to keep it moving? energy is not created or destroyed. when you are staying still on a level street and have to start pedaling there is currently no energy forcing that bike to get it going excpet for the energy you are forcing onto it but once it gets going fast with foward momentum it gains kinectic energy. the more mass an object has the more energy it will take to get it going. but at the same time the more mass an object has the more kinectic energy it will gain when it get moving. an object in motion stays in motion until some kind of force acts upon it. an object at rest stays at rest until a force acts upon it. you see you cannot create or destroy energy. if you wanted to ride a bike uphill you would have to use alot of energy to get up that hill and once you got to the top you would be exhasuted. but wait you will be rewarded or your hard work because you put that energy into going up the hill you will get it back going superfast back down the otherside of the hill without having to pedal. you just experienced kinetic energy going down that hill. and it was alot easier going down that hill then it was when you first started going up it. this same concept appplies to riding a bike on level ground. all it is is that when you first start you have to use alot of energy to get the object moving but once it gets moving it will get kinetic energy from graivty and it will keep going. see if you were on level ground and pedaled as fast as you can for 5 seconds then stopped pedaling your bike would keep coasting along ways. say 40 ft maybe more.....why because.....energy is not created or destroyed. your body turned chemical energy into force that got the bike moving and that energy will be converted into kinectic energy wind energy and friction. because of the enrgy you had to use to move the mass of yourself and your bike if you were to stop pedaling that energy would still exist in the form of kinectic energy. so tou answer your question in short. it is because you used enrgy to get the bike moving and that energy will never be destroyed so it will be turned into kinectic energy. which is the bike moving itself by the force of gravity. because gravity acts on all objects the higher the mass the higher the kinectic energy This is because the coefficient of static friction (to get the bike moving) is higher than the coefficient of kinetic friction (to keep the bike moving) therefore, the force of friction would be higher because of the equation : Force of Friction = (coefficient of static/kinetic friction) x (The Normal Force). Hope I helped. AP Physics Class Gotta disagree with Lindsey. It's because when starting the bike moving you need to accelerate it and yourself. F = ma. Besides that you have some friction in the bike and your knees etc to overcome. Once you're just maintaining a constant speed, you don't need any force to go to acceleration - just overcoming friction. |
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