Physics 101: week 2, 8/23
Physics 101: week 2, 8/23 Physics 101
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This 3 page Class Notes was uploaded by Kate Worley on Tuesday August 23, 2016. The Class Notes belongs to Physics 101 at University of Tennessee - Knoxville taught by Kranti Gunthoti in Fall 2016. Since its upload, it has received 101 views. For similar materials see How Things Work in PHYSICS (PHY) at University of Tennessee - Knoxville.
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Date Created: 08/23/16
Physics 101 Notes: 8/23 Skates o Riding a skateboard allows you to move freely, with ease and simplicity, without the constraints of friction o The skates support you vertically, because the ground supports the skates and the skates support you. But unlike shoes, the skates move freely back and forth o Skating is an example of the principle, Inertia: an object at rest tends to remain at rest, and object in motion tends to stay in motion. Why does a stationary skater remain stationary? o An object at rest tends to stay at rest (inertia) o Question: “A rotary lawnmower spins its sharp blade rapidly over the lawn and cuts the tops off the grass. Would the blade still cut the grasses if they weren’t attached to the ground? Yes, because even though it is not attached to the ground, it will stay in place because of inertia, allowing the blade to cut the grass. Why does a moving skater tend to keep moving? o An object in motion tends to remain in motion (inertia) o Inertial objects: inertial objects move in a straight line with a steady pace. o Objects at rest are still at a steady pace of motion (steady pace is 0) Newton’s First law of Motion o “An object that is free of external influences moves in a straight line and covers equal distances in equal times.” o Question: Which one of the following is moving according to Newton’s first law of motion? A. A skater moving straight toward a flagpole and speeding up B. A skater moving straight forward and slowing downC. A skater moving in a circle at a steady speed D. A skater who is experiencing zero force Position o The measure of an object’s location in space o For position, you need: Reference point Distance from the reference point Direction from the reference point o S.I unit of distance is meter o “Physical quantities like position have both amount and direction” Vector quantities Speed o Rate at which an object covers distance o S= d/t (distance divided by time) o Dividing the total distance travelled by the object, by the total time it travelled, will give you the speed, or velocity, at which the object is travelling o If you travel 60 miles in 2 hours, then you average speed is 30 miles per hour (60/2=30) o Based on the information given to you, you can reword the equation in different ways If we know the car is travelling at 55 miles per hour and it travelled for 3 hours, you divide speed by time to get the distance (d=s/t). So you know the car travelled for 165 miles. If you know the car travelled for 220 miles at 55 miles per hour, you divide the distance by the speed to get the time. (t=d/s). So you know the car travelled for 4 hours. o The units are always carried along the calculations and treated as algebraic quantities o Units are standard quantities such as seconds, meters, or miles o The most common units are those of the international system (SI), which contains meters, seconds, and kilograms Velocity o The rate at which the position of an object changes o Velocity is a vector quantity (direction), speed is a scalar quantity (no direction) o Measured with distance/time (miles/hour) o Average velocity of an object: “the displacement of the object divided by the time at which the displacement occurred “ (v=Dx/Dt)=((x2-x1)/t2-t1)). The x’s are the starting and end points, t’s are the starting and end times. o A runner runs a mile around the track in 5 minutes. What is his average velocity? What is his average speed? Velocity: the velocity is zero, because he did not cover any distance because his starting and ending points were the same Speed: 1 mile/5 min 12 mi/ 60 minutes (1 hour) 12 miles per hour In order to convert to miles per hour, you had to multiply 5 min by 12 to get to 60 minutes, or one hour. Because you did that, you also have to multiply 1 mile by 12, which leaves you with 12 miles per hour. o A car drives north for 35 minutes at 85 km/hour and stops for 15 minutes. He continues, traveling 130 km in 2 hours. What is the total distance? What is his average velocity?
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