How is motion measured and described?
In this unit students investigate and describe the motions of people and objects in everyday situations such as sporting events. Initially, students measure the distance traveled during equal time intervals for objects traveling at a variety of constant speeds. Next, they measure the distance an object moves in equal time intervals when it is speeding up and slowing down. This distance and time data for various moving objects are used to make distance vs. time line graphs to represent these motions, along with motion diagrams, to show the positions at equal time intervals. These graphs are then used to develop the relationship between the slope of the graph and the speed of the object. Specifically, constant slope means constant speed and changing slope means changing speed. Students also use the formula for average speed to compare the motions that were measured. They then construct velocity vs. time graphs to represent these same motions and use given velocity vs. time graphs to construct verbal descriptions of motion. Last, students investigate circular motion by identifying and representing on diagrams the center seeking, or centripetal force, required to maintain circular motion in a frictionless environment. In each case, the primary objective is to develop the understanding that all motion is measured in terms of distance traveled in a fixed time interval and to relate this understanding to the concepts of average speed, constant speed, and acceleration.
STANDARD P2: MOTION OF OBJECTS The universe is in a state of constant change. From small particles (electrons) to the large systems (galaxies) all things are in motion. Therefore, for students to understand the universe they must describe and represent various types of motion. Kinematics, the description of motion, always involves measurements of position and time. Students must describe the relationships between these quantities using mathematical statements, graphs, and motion maps. They use these representations as powerful tools to not only describe past motions but also predict future events.
P2.1 Position — Time
P2.1A Calculate the average speed of an object using the change of position and elapsed time.
P2.1B Represent the velocities for linear and circular motion using motion diagrams (arrows on strobe pictures).
P2.1C Create line graphs using measured values of position and elapsed time.
P2.1D Describe and analyze the motion that a position-time graph represents, given the graph.
P2.1E Describe and classify various motions in a plane as one dimensional, two dimensional, circular, or periodic.
P2.1g Solve problems involving average speed and constant acceleration in one dimension.
P2.1h Identify the changes in speed and direction in everyday examples of circular (rotation and revolution), periodic, and projectile motions.
P2.2A Distinguish between the variables of distance, displacement, speed, velocity, and acceleration.
P2.2B Use the change of speed and elapsed time to calculate the average acceleration for linear motion.
P2.2C Describe and analyze the motion that a velocity-time graph represents, given the graph.
P2.2D State that uniform circular motion involves acceleration without a change in speed.
P3.4 Forces and Acceleration
P3.4D Identify the force(s) acting on objects moving with uniform circular motion (e.g., a car on a circular track, satellites in orbit).
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- How do scientists describe the motion of objects?
- How can the motion of objects be represented by line graphs, motion diagrams, and formulas?
- How are average speed, distance traveled, and acceleration calculated using appropriate formulas and graphs?
- What causes objects to move in circular paths?
graphs of motion
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