C Kitchens Physical Science E06 Measuring Motion: Distance, Displacement, Speed and Velocity C Kitchens Physical Science E06 thecancermademedoit.com

Motion Motion is a change in position in a certain amount of time To accurately describe motion, one must first consider the frame of reference Frame of reference = a system of objects that are not moving with respect to one another

Motion Relative Motion = an objects motion depends on the frame of reference…so it is relative to the frame of reference. For example, people moving in a car do not seem to be moving in reference to each other, but are moving at a definite speed in reference to people standing on a sidewalk. You must choose a frame of reference that allows you to give a clear and relevant description of the motion. schoolphysics.co.uk

Motion Distance is the length of a path between 2 points The SI unit for distance is the meter (m). For longer distance, the kilometer (km) is often used. For smaller distances, you might see the centimeter(cm) or millimeter(mm). googlesystem.blogspot.com

Motion Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.  Displacement is an example of a vector, which is a quantity that includes magnitude and direction. Displacements in the same direction are added Displacements in the opposite direction are subtracted. en.wikipedia.org

Practice Problem A cross country runner leaves school for a 10-mile run. They end their run at a Dairy Queen one mile from school. What is the total distance they ran? What is their displacement?

Practice Problem An RV travels 45 km east and stays the night at a KOA. The next day it travels for 3 hours to the north, traveling 110 km. What is the displacement over the two days for the RV?

Motion Displacement vectors that have different directions can be combined by graphing, with the vector that shows the sum of the displacements being called the resultant vector. physicsclassroom.com

Practice Problem If Vx = 6.8 units and Vy = 7.40 units, determine the magnitude of the displacement vector. Draw a diagram.

Motion 123rf.com Speed is the rate at which an object moves, or the ratio between the distance and time of movement.   Speed = distance v = d time t The SI unit of speed is meters per second, m/s

Practice Speed The Midnight Express heading west from Chicago to Albuquerque travels at 100 mph for 160 miles. How much time does this take?

Motion Constant speed is the speed that does not change. A graph of constant speed is a straight line. racebrakes.co.nz giganticinflatables.com

Motion Average speed is the total distance divided be the total time. Average Speed is computed for the entire trip, and instantaneous speed is for a particular instant. A graph of average speed is not a straight line. (flat line shows that the object is stopped) www.allthink.com

Average Speed Problem #1 A student practicing for a track meet ran 250 meters (m) in 30 seconds (s). What was her average speed?

Average Speed Problem #2 Goliath chased a squirrel through the backyard. He followed the squirrel’s scent for 10 minutes and traveled 900 feet. He lost the scent and stood for 2 minutes while he tried to find it again. Once he found the scent, he ran 300 feet in 1.75 minutes. What was Goliath’s average speed while he chased the squirrel?

Motion Velocity is speed in a given direction ex. 10 m/s, west Velocities in the same direction are added. Velocities in opposite directions are subtracted. www.clccharter.org  www.physicsclassroom.com

Practice Velocity An aircraft carrier traveled 4,727 kilometers east in 83 hours. What was the ship’s velocity in kilometers per hour?

Motion Velocities in 2 directions that are at angles can be used to calculate the resultant velocity by setting them up end to end and then solving for the 3rd vector. (a2 = b2 + c2) A motorboat traveling 4 m/s, East encounters a current traveling 7.0 m/s, North. What is the resultant velocity of the motorboat? If the width of the river is 80 meters wide, then how much time does it take the boat to travel shore to shore? What distance downstream does the boat reach the opposite shore?

Answer: The resultant velocity can be found using the Pythagorean theorem. The resultant is the hypotenuse of a right triangle with sides of 4 m/s and 7 m/s. It is [ (4 m/s)2 + (7 m/s)2 ] = 8.06 m/s b. The time to cross the river is t = d / v = (80 m) / (4 m/s) = 20 s c. The distance traveled downstream is d = v • t = (7 m/s) • (20 s) = 140 m