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Discussion and Debate
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Drill sergeants in classrooms?
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<blockquote data-quote="keith99" data-source="post: 76845292" data-attributes="member: 211648"><p>Since some have asked for real world illustrations of how knowing physics is useful here are a few. </p><p></p><p>Once upon a time playgrounds had little merry-go-rounds that you had to push. Understanding the conservation of angular momentum allowed kids to get it going faster than tehy could possibly push it, faster than they could run! Kids woudl push it and then jump on, near the edge, Then as they moved towards the middle it would rotate much faster. Pity the kid who was last to move to the center. </p><p></p><p>Knowing that the coeffecient of static friction is greater than the coeffecient of dynamic friction has many uses. Sliding that sofa, box or fridge really is easier once it starts moving, e.g. when things change from static to dynamic friction. The same thing happens with starting or stopping a car. Starting if the wheels spin the car actually accelerates less than it would otherwise. Stopping if you lock up the wheels and skid it actually takes longer to come to a stop than if the wheels keep turning and it is the coeffecient of static friction that matters. </p><p></p><p>If you lean a ladder on a wall or side of your house it is pretty obvious that the bottom of the ladder should bo a ways out from the wall at the bottom, otherwise you could easily fall backwards. At first glance it might seem that the farther away the better. That is not true. Too far back and the ladder can slide down if there is enough horizontal force at the base to overcome the static friction. Fortunately in most cases coeffecient is high enough that it is not a problem at any angle that is at all reasonable. But with a wood ladder on a slick tile floor it can easily happen. And if you think it could happen knowing that once it starts moving it is again the coeffecient of dynamic friction that matters shoudl alert yuo to the fact that once it starts it is too late to stop. So if in doubt it is wise to ahve someone keeping the ladder from starting to slide at all times. </p><p></p><p>Of course anything that is common has been 'solved' long ago and one can learn it by just imitating others or learning from others, who do not understand the physics behind it. But actually knowing the physics can often be what allows you to seperate fact from fiction in what others tell you.</p></blockquote><p></p>
[QUOTE="keith99, post: 76845292, member: 211648"] Since some have asked for real world illustrations of how knowing physics is useful here are a few. Once upon a time playgrounds had little merry-go-rounds that you had to push. Understanding the conservation of angular momentum allowed kids to get it going faster than tehy could possibly push it, faster than they could run! Kids woudl push it and then jump on, near the edge, Then as they moved towards the middle it would rotate much faster. Pity the kid who was last to move to the center. Knowing that the coeffecient of static friction is greater than the coeffecient of dynamic friction has many uses. Sliding that sofa, box or fridge really is easier once it starts moving, e.g. when things change from static to dynamic friction. The same thing happens with starting or stopping a car. Starting if the wheels spin the car actually accelerates less than it would otherwise. Stopping if you lock up the wheels and skid it actually takes longer to come to a stop than if the wheels keep turning and it is the coeffecient of static friction that matters. If you lean a ladder on a wall or side of your house it is pretty obvious that the bottom of the ladder should bo a ways out from the wall at the bottom, otherwise you could easily fall backwards. At first glance it might seem that the farther away the better. That is not true. Too far back and the ladder can slide down if there is enough horizontal force at the base to overcome the static friction. Fortunately in most cases coeffecient is high enough that it is not a problem at any angle that is at all reasonable. But with a wood ladder on a slick tile floor it can easily happen. And if you think it could happen knowing that once it starts moving it is again the coeffecient of dynamic friction that matters shoudl alert yuo to the fact that once it starts it is too late to stop. So if in doubt it is wise to ahve someone keeping the ladder from starting to slide at all times. Of course anything that is common has been 'solved' long ago and one can learn it by just imitating others or learning from others, who do not understand the physics behind it. But actually knowing the physics can often be what allows you to seperate fact from fiction in what others tell you. [/QUOTE]
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