Motion Describing Position How would you tell someone

Motion

Describing Position • How would you tell someone where our school is located? In all ways you would be stating its location relative or compared to something else. Ex. GMS is located next to GHS. It is 6 miles north of the city of Madison. It is off the exit before you get to Nissan. The particular point you used to describe GMS’s location is your REFERENCE POINT. A position is the object’s distance and direction from the reference point.

Describing Position • Since position is the distance and direction of an object from a reference point if the reference point changes, the distance and direction from the reference point might change. • See figure 1 page 340

Describing Position A complete description of an object’s position includes: • A distance • A direction • A reference point -Examples of describing position in the real world: • Surveyors • GPS

Describing Changes in Position • Motion is the change in position in a certain amount of time. • We describe motion with words such as speed, velocity and acceleration.

Speed - DISTANCE an object travels Per unit of TIME You calculate speed by dividing the distance by the time. 50 meters/2 seconds

Units used to measure speed • Meters/seconds • Kilometers/hour ******remember we use the metrics in science******

Roller Coaster • https: //www. bing. com/videos/search? q=short+video+of+a+roller+co aster&&view=detail&mid=9 D 29 EA 852 CD 8 A 512684 C&&FORM=VDRVRV

Types of Speed • Constant Speed-when an object travels the same distance each second. An example of this is when the “cruise control” is used. • See figure 6 on page 348

Types of Speed • Instantaneous speed-the speed of an object at an exact instant in time. You see instantaneous speed on the speedometer in a car. • See figure 6 page 348

Types of Speed • Average Speed-the total distance traveled by the total time it took to travel that distance. • This is how we normally travel-you speed up and slow down often. Imagine walking in the hall during class change. You would find your average speed.

Calculating Average Speed • It takes Chris 60 seconds on his bicycle to reach his grandmother’s house 300 meters away. What is his average speed?

Calculating Average Speed • It takes Chris 60 seconds on his bicycle to reach his grandmother’s house 300 meters away. What is his average speed? Distance = 300 meters Time =60 seconds D/T 300 m/60 s=5 m/s Answer-the average speed is 5 meters per second.

Distance-Time Graphs that compare distance and time are called Distance-Time Graphs. Constant Speed is shown as a STRAIGHT line on the graph. See figure 7 page 350 The measure of steepness of the line is called the slope. The steeper lines on distance-time graphs mean faster speeds. See figure 8 page 351

Distance-Time Graph and CHANGING Speed Notice the RED line-it is not a straight line because this is not constant speed but shows how speed changes as we travel. When the line is HORIZONTAL it indicates there is no motion so no distance traveled during that time. You could find the AVERAGE SPEED of the object indicated by the red line. See Figure 10 page 352

Velocity Sometimes speed is not enough to describe the motion of an object. Sometimes it is important to also know the object’s DIRECTION. Velocity is speed in a given direction. Think of a tornado. It is very important to know what SPEED it is moving and in what DIRECTION it is traveling. Example-80 m/s West

Velocity • Velocity changes any time speed or direction change. So if the object speeds up, slows down, or changes directions the velocity changes. • An object traveling at a constant 30 m/s in a circle IS changing its velocity because even though it is not changing its speed IT IS changing direction.

Acceleration The rate(time) at which velocity changes is Acceleration. So if you speed up, slow down or change direction you are accelerating.

Acceleration is the change in velocity divided by the time it takes to change the velocity. It is expressed as m/s/s or Meters/second or m/s 2 Remember velocity is speed in a given direction-so there is the m/s. But acceleration is the TIME it takes to CHANGE velocity, so you add another unit of time (s) which makes it s 2.

Calculating Acceleration Final speed – initial (beginning) speed Total time A plane sped up from 500 m/s to 900 m/s in 2 seconds. What was the acceleration of the plane? Final speed was 900 m/s. Initial speed was 500 m/s. Time this took was 2 seconds total. So FIRST subtract the speeds. 900 -500 = 400 m/s. THEN divide that answer by the time it took-2 seconds. Answer is then 200 m/s/s. The plane accelerated 200 meters each second for 2 seconds.

Acceleration • Positive acceleration is speeding up • Negative acceleration is slowing down or speeding up in REVERSE

Speed-Time Graph • A speed-time graph measures speed and time instead of distance and time. Always look at your x and y axis! • A speed-time graph shows how speed changes over time.

Different Graphs Look at the first two graphs on the left. The top one shows a horizontal line to show an object not moving because the distance does not change. But on the bottom graph, the speedtime graph, the horizontal line is at zero because if the object is at rest (not moving) then its speed is zero.

Different Graphs The second set of graphs shows objects at constant speed. The third set of graphs shows objects speeding up. The last set of graphs shows objects slowing down.