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Motion Chapter 12 12-1 Frames of Reference I can explain why all motion is relative. When describing something that is moving, you are comparing it with something that is assumed to be stationary (not moving). The frame of reference is the background or object that is used for comparison. Ex: You are on a train that just left the platform. The people standing on the platform see you moving away. (earth) The person sitting next to you does not see you moving. (train) Frame of reference depends on the type of movement and position from which you are observing. An actor may be standing still and the background is moving, but to us we think the actor is going somewhere. We assume the background is stationary. Earth is the most commonly used frame of reference. 12-1 Frames of Reference I can explain why all motion is relative. Book Work 12.1 Section Review Page # 301 1-4 Vocabulary: 12.1 WS Frame of Reference 12.2 Measuring Motion I can define motion and speed. I can calculate speed, using the formula speed = distance/time. I can distinguish between constant speed and average speed. I can represent speed graphically as distance/time. I can distinguish between speed and velocity. Motion Motion is a change in position in a certain amount of time. When you say that something has moved, you are describing motion. In describing motion, you are comparing it with some frame of reference. Speed In a race, the runners had to move or change positions to get to the finish line in a certain amount of time. To describe motion you need to know: traveled (meters – m) how long it took to go that distance (seconds – s) distance Speed Speed is the rate at which an object moves. The faster a runner’s rate of motion, the faster the runner’s speed. Speed Units = distance/time = m/s Constant Speed Objects in motion that their speed does not change is moving at a constant speed. Total distance divided by total time give speed at any point in time. Graph is a straight line for constant speed. Problem At what speed did a plane fly if it traveled 1760 meters in 8 seconds? Steps: – Write a formula 2 – Substitute given numbers and units 3 – Solve for the unknown 1 Average Speed Not all objects move at constant speeds. The average speed also uses the formula speed = total distance/ total time Going to Columbus, you change speeds during the drive many times. So over all you travel at an average speed. Let’s Practice Calculating Motion #1. 800m, 60s 13.3 m/s #2. 472m, 15s 31.45 m/s #3. 2500m, 110s 22.72 m/s Velocity Velocity is speed in a given direction. It is also determined by using the distance from the starting position to the ending position, rather than the distance of the path taken. A runner moves eastward at 10m/s. speed is 10m/s velocity is 10m/s east Velocity is very important for airplane pilots, weather forecasters and anyone driving from one place to another. 12.2 Measuring Motion I can define motion and speed. I can calculate speed, using the formula speed = distance/time. I can distinguish between constant speed and average speed. I can represent speed graphically as distance/time. I can distinguish between speed and velocity. Book Work 12.2 Section Review Page # 308 1-4 Vocabulary: motion, speed, velocity Worksheet: 12.2 Review Lab 12.3 Changes in Velocity I can define acceleration and deceleration. I can calculate acceleration and deceleration using the given formula. I can interpret the distance/time graph for acceleration. I can describe circular motion. Acceleration The rate of change in velocity is known as acceleration. If something is accelerating, it is doing one of the following: speeding up slowing down changing directions Acceleration 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 = 𝒇𝒊𝒏𝒂𝒍 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚 −𝒐𝒓𝒊𝒈𝒊𝒏𝒂𝒍 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒕𝒊𝒎𝒆 Final = ending velocity Original = starting velocity It tells how fast something is moving and gives direction. Used when there are changes in velocity. Problem A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster? Steps: – write the formula 2 – substitute given numbers and units 3 – solve for the unknown 1 Deceleration When there is a decrease in velocity, the value of acceleration is negative. Negative acceleration = deceleration – time graphs for acceleration is always a curve. Distance Circular Motion In circular motion, the velocity is continuously changing because direction is continuously changing. An object in circular motion is accelerating even though its speed may be constant. Ex: Ferris wheel, traveling in a car turning a corner, or even as you sleep (the earth is continuously rotating) 12.3 Changes in Velocity I can define acceleration and deceleration. I can calculate acceleration and deceleration using the given formula. I can interpret the distance/time graph for acceleration. I can describe circular motion. Book Work Calculating 12.3 Section Review Page # Acceleration Worksheet 313 1-5 Vocabulary: 12.3 acceleration review worksheet 12.4 Momentum I can define momentum. I can calculate momentum, using the equation momentum = mass X velocity. I can explain the law of conservation of momentum. Momentum A 100kg fullback runs up the middle of the football field and collides with a 75kg defensive back running towards him. The more massive fullback is thrown back 2 meters. How can a 75kg defensive back stop a 100kg fullback? - The defensive back has more momentum. All moving objects have momentum. The more momentum, the harder to stop the object. Momentum depends on the mass of the object and the velocity with which it is traveling. Momentum Units = mass x velocity = kg-m/s Momentum Train has large momentum because of it’s mass. A bullet fired from a rifle also has large momentum but because of it’s very high velocity. Conservation of Momentum The total momentum of any group of objects remains the same unless outside forces act on the objects. If one object loses momentum then another object must gain momentum. Momentum is always conserved. Conservation of Momentum Total momentum of two billiard balls before they hit and after they hit must be the same. Individual momentum can change even though total momentum remains. Ex: if one ball speeds up after they hit, the other must slow down. Examples The momentum of a baseball bat is transferred to the ball when the bat and the ball meet. The act of throwing an object off a boat causes the boat to move in the opposite direction. The more massive the object and the faster it is thrown, the faster the boat will move away. 12.4 Momentum I can define momentum. I can calculate momentum, using the equation momentum = mass X velocity. I can explain the law of conservation of momentum. Book Work 12.4 Section Review Page # 316 1-5 Vocabulary: Worksheet momentum Chapter Review – Page 320 Multiple Choice # 1-5, 7-10 True/False # 1-5, 7, 8 Concept Master #3 Critical – Correct the false #1 Thinking