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Describing and Measuring Motion Objects in motion may not be as they appear, or are they? ?
MOTION Motion is defined as the change of position over time. A change in position is evidence that motion has happened.
Reference Points A reference point is a place or object used for comparison to determine if something is in motion. An object is in motion if it changes position relative to a reference point. Objects that we call stationary—such as a tree, a sign, or a building—make good reference points.
Relative Motion How do you know if you are moving? It’s all relative to your reference point. If your chair is the reference point, then all of you are NOT moving, BUT…. …suppose you choose the sun as a reference point? If you compare yourself to the sun, then you are moving quite rapidly. This is because you, and your chair are on Earth, which moves around the sun. Earth moves about 30 kilometers every second.
Choosing a Reference Point to Determine Location 1. You may choose a specific stationary location. For example, you might say; Freehold Borough is 20 miles West of Ocean Township. Amy’s house is 1 block south of John’s house. Jane is sitting 10 feet North of the big Oak tree in the field.
OR…… 2. You may use the Longitude and Latitude System, where location is described by how many degrees north or south it is from the equator and how many degrees east or west it is from the prime meridian. The reference point is 0 degrees longitude and 0 degrees latitude. All global locations can be determined using this system.
Moving Reference Point You probably know what happens if your reference point is moving. Have you ever been in a car and feel like you are moving backwards, but, then you realize that it is the other car that is moving? ? ? Your car seemed to move backwards because you were using the other car as a reference point.
Figure 1 Reference Points The passenger can use a tree as a reference point to decide if the train is moving. A tree makes a good reference point because it is stationary from the passenger’s point of view.
The apparent motion of an object depends on the observer’s motion. p. 8
Think about it… If Kyle walks 3 blocks south from his home to school, and Jen walks 2 blocks north from her home to Kyle’s home, then how far, and in what direction is the school from Jen’s home?
SPEED Average speed = How far you have traveled in a given amount of time. Speed = Distance Time Instantaneous Speed = speed at that very moment in time
Calculations…. . Pay Attention to your Units! You have driven 100 miles in 2 hours what is your speed? You have been driving for 20 minutes and have gone 60 miles, what was your speed. It has taken you 12 minutes to go 72 kilometers, How fast are you moving? Speed = Distance Time
Speed Calculations: What is Mr. Brovak’s speed if he has traveled 200 kilometers in 20 minutes? Ms. O’Rourke is rowing a boat, what is her speed if she has gone 56 meters in 8 minutes? Mrs. Cholak is chasing Ms. O’Rourke down the hallway to get one of her awesome cupcakes, how fast is she going if she has run 60 meters in 12 seconds Ms. Michel has run out to go to the mall. What is her speed if it takes her 25 minutes to go 400 meters?
Velocity = Speed in a given direction Example: The car is traveling 55 m/h North The plane is flying 1200 kilometers/minute East