The Physics of Trick or Treating
Halloween should really be a celebration of physics. I mean you couldn't ring the doorbell without pushing it and this action right here my friends is called a force. And when the person opens their door they too are applying a force. Their door would choose to stay at rest but because it was acted upon by a net force- the person pushing it open- it opens instead. Now let's get to the most important part: the candy. When the person drops candy into your bag, the candy is in free fall. You can even calculate the final velocity of the candy as it hit the other pieces of candy in your bag. Lets suppose the person's hand is .10 meters above your candy bag. and since the candy is in her hands it starts with a velocity of 0. and since gravity pulls things down at 9.81 m/s2 this would be the acceleration if we call downward the positive direction. Using the formula
vf2 = vi2+ 2ad we can substitute with units and solve to get the the final velocity of the candy vertically is 1.4 m/s. And we can also figure out how long it takes for the candy to fall to the bottom of the bag so you can hurry up and go to the next house using the formula, d= vit + (1/2)at2 which can be rearranged to t2 = 2d/a since our initial velocity equals zero. and when you substitute with units you will find that time =.14 seconds. Meaning it only takes .14 for the piece of candy to fall to the bottom of your bag. And you can thank physics that this candy stays in your bag. The force of gravity is pulling your candy down but the bag, the normal force and your arms which act as tension are acting in opposition to the force of gravity and preventing your candy from ending up on the floor. When you run door to door you are accelerating. And when you stop quickly so that you don't collide with the door you have a negative acceleration. and if someone ask you if walking 10 block to collect candy was worth it just tell them "what are you talking about i started at home and ended at home so really my displacement was zero so yeah it was worth it"
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