Vocabulary

Chapter 11 > |||| **Figure 3**  When motion is in a straight line, vectors add and subtract easily. **A** Add the magnitudes of two displacement vectors that have the same direction. **B** Two displacement vectors with opposite directions are subtracted from each other. > >, is the total distance traveled, //d,// divided by the time, //t,// it takes to travel that distance. This can be written as an equation: >
 * VOCABULARY**
 * To describe motion accurately and completely, a frame of reference is necessary. The necessary ingredient of a description of motion—a **frame of reference**—is a system of objects that are not moving with respect to one another.
 * **Relative motion** is movement in relation to a frame of reference. For example, as the train moves past a platform, people standing on the platform will see those on the train speeding by. But when the people on the train look at one another, they don't seem to be moving at all.
 * **Distance** is the length of a path between two points. When an object moves in a straight line, the distance is the length of the line connecting the object's starting point and its ending point.
 * Displacement is an example of a vector. A **vector** is a quantity that has magnitude and direction. The magnitude can be size, length, or amount. Arrows on a graph or map are used to represent vectors. The length of the arrow shows the magnitude of the vector. Vector addition is the combining of vector magnitudes and directions.
 * |||| [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsp00414c04.gif]] ||  ||
 * The vector in red is called the **resultant vector**, which is the vector sum of two or more vectors.
 * **Speed ** is the ratio of the distance an object moves to the amount of time the object moves. The SI unit of speed is meters per second (m/s). However, just as with distances, you need to choose units that make the most sense for the motion you are describing. The in-line skater in Figure 5 may travel 2 meters in one second. The speed would be expressed as 2 m/s. A car might travel 80 kilometers in one hour. Its speed would be expressed as 80 km/h.
 * **Average speed **,
 * **Average speed **,
 * The car's speedometer gives your instantaneous speed. **Instantaneous speed **, //v,// is the rate at which an object is moving at a given moment in time. For example, you could describe the instantaneous speed of the car in Figure 6 as 55 km/h.
 * Together, the speed and direction in which an object is moving are called **velocity **. To determine how long it will be before the cheetah reaches the antelope, you need to know the cheetah's velocity, not just its speed. [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsps_key_bodytext_logo.png caption="Key Concept"]] Velocity is a description of both speed and direction of motion. Velocity is a vector.
 * The rate at which velocity changes is called **acceleration **. Recall that velocity is a combination of speed and direction. [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsps_key_bodytext_logo.png caption="Key Concept"]] Acceleration can be described as changes in speed, changes in direction, or changes in both. Acceleration is a vector.
 * An example of acceleration due to change in speed is **free fall **, the movement of an object toward Earth solely because of gravity.
 * The velocity of an object moving in a straight line changes at a constant rate when the object is experiencing constant acceleration. **Constant acceleration ** is a steady change in velocity.
 * Figure 16 is an example of a **linear graph **, in which the displayed data form straight-line parts. The slope of the line is the acceleration.
 * [[image:file:hsp00432c04.jpg]][[image:hsp00432c04.jpg]]


 * * In a **nonlinear graph **, a curve connects the data points that are plotted. Figure 18 is a distance-time graph. The data in this graph are for a ball dropped from rest toward the ground. ||
 * [[image:http://www.pearsonsuccessnet.com/ebook/products/0-13-069977-2/hsp00434c04.gif]] ||  ||
 * **Figure 18** A distance-time graph of accelerated motion is a curve. ||

Flashcards for [|Force and Motion]