1. Distance and Velocity Chapter 11.1 Notes

2. Objects in Motion Motion is all around us—from a car driving in a straight line to a satellite circling the earth; describing motion in science requires certain vocabulary We observe the motion of an object in relation to other objects that do not move, called reference points The frame of reference is used to describe the motion of an object relative to the reference points When an object changes position with respect to a frame of reference, the object is in motion You can describe an object‘s motion with direction, such as, north, south, east, west, up, down, etc.

3. Distance vs. Displacement In order to correctly describe the motion of an object, you need to know its direction and how far the object moves Distance is a measure of the length of the path the object took Displacement is a change in the object’s position—if a student runs around a soccer field, the distance is the total length of the path traveled; the displacement is only the difference between the starting and ending points

4. Distance vs. Displacement

5. Distance: measures how far an object moves along a path The distance between your home and school is 12 blocks Distance is a scalar—it can be described with only numerical values Displacement: measures how far it is between an object’s starting and ending points Often shorter than distance Requires a direction: you walk 12 blocks towards the school Displacement is a vector—it has both a magnitude (number) and direction

6. Speed vs. Velocity Speed describes how fast an object moves Velocity describes an objects speed and direction of motion Direction is described as positive or negative along the line of motion; so if an object is moving in one direction it will have positive velocity, if it is moving in the opposite direction it will have negative velocity Moving to the right or up are usually positive, moving to the left or down are usually negative

7. Calculating Speed To calculate speed, you need to know the distance traveled and the time it took to travel that distance The SI unit for speed is meters per second (m/s) Speed=distance/time Velocity is an objects average speed—remember, velocity has to have a direction! Velocity=displacement/time Units are still m/s Instantaneous speed is the speed at a given time—the speed measured over a very small time interval

8. Graphing Motion Motion can be shown on a graph by placing distance on the y-axis and time on the x-axis The dependent variable is on the y-axis; the distance traveled depends on how much time there is The independent variable is on the x-axis; time will pass whether an object moves or not The slope of a distance vs. time graph is equal to the speed If an object is moving at a constant speed, the graph is a straight line The steeper the slope, the faster the speed of the object