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This chapter covers motion diagrams, coordinate systems, velocity, and acceleration. It includes a mini-lab on measuring constant speed and modeling real-life situations. The concepts of vectors, scalars, displacement, time intervals, and velocity are discussed.
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Chapter 3 Describing Motion
3.1 Picturing Motion • Motion Diagrams • A series of images of a moving object that records its position after equal time intervals. • The Particle Model • Replacing the object with a single point.
Mini-lab • Using the ticker-tape timer, determine the constant speed you are able to pull the tape. • Repeat the lab but this time slowly increase the speed with which you pull the tape. What do we call this type of motion? • Plot the distance from the starting point to every sixth dot on the tape (1/10 of a second for each sixth dot).
Review • Answer the following questions in your lab book. • 1. What did you notice about the shape of the graphs? • 2. Why were they not an exact fit to the line generated? • 3. Describe how we could use this to model real life situations? • Compare your answers with your groups’ and whiteboard group consensus.
3.2 Where and When • Coordinate systems • Tells you where the zero point is located. • Vectors and Scalars • Something that only tells you the magnitude is a scalar quantity. • A vector has both magnitude and direction
Time Intervals and Displacements • Displacement defines both the distance and direction between two positions and is therefore a vector. • ∆t is the time interval(t1 – t0) • ∆d is the change in displacement (d1 – d0)
3.3 Velocity and Acceleration • Velocity • Average velocity vis the change in position divided by the time it took to make the change. • v≡∆d/ ∆t = d1 – d0 / t1 – t0 • Instantaneous velocity • The velocity at any given point in time. • Average velocity motion diagrams
Acceleration • An object whose velocity is changing is said to be accelerating. • Average acceleration • a≡∆v/ ∆t = v1 – v0 / t1 – t0
PSS 1. Sketch the problem. Establish a coordinate system and add it to your sketch. Reread the problem and make a list of unique symbols to represent each of the variables that are given or known. Decide which quantities are unknown and give them symbols. Create a physical model. Use this as a motion diagram.
2. Calculate your answer. Use the physical model as a guide to the equations and graphs you will need. 3. Check your answer. Did you answer the question? Does the answer appear reasonable?