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1-2 Measuring Motion. What is Motion?. A change in position in a certain amount of time When you describe movement, or motion, you are comparing it with a frame of reference. What is speed?. Speed is the rate at which an object moves. The faster the rate of motion the faster the speed.
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What is Motion? • A change in position in a certain amount of time • When you describe movement, or motion, you are comparing it with a frame of reference.
What is speed? • Speed is the rate at which an object moves. The faster the rate of motion the faster the speed. • In order to solve for speed you need to know the distance traveled and the time. • The formula for speed is Speed = distance time
What are the units for speed? • Distance is measured in meters or kilometers • Time is measured in seconds or hours • So the unit for speed is meters/second (m/s) or kilometer/hour (km/hr) • From the sun’s frame of reference Earth is orbiting 30 kilometers per second (30 km/sec)
Constant speed • Speed that does not change is called constant speed. • A graph of constant speed is a straight line (through the origin) A car travels 150 km/s in 5 seconds. What is the speed of the car?
Average Speed • When the speed of a moving object is not always constant you calculate the average speed. • To calculate average speed you divide TOTAL DISTANCE by TOTAL TIME Average speed = total distance / total time
Velocity • Velocity is speed in a given direction. • Mrs. T runs 10 m/s east. • What is her speed? • What is her velocity? • Mrs. McD. jumps 2 m/s up • What is her speed? • What is her velocity?
Combining Velocities • If two object are moving in the same direction in relation with each other (such as a river and boat ) there velocities combine. • If you are rowing a boat downstream at 10 km/hr and the river is also moving at 10 km/hr downstream, then you are actually travelling at a rate of 20 km/hr
Combing Velocities • If two object are moving in different direction in relation with each other (such as a boat traveling upstream on a river) there velocities subtract. • If you are paddling a boat upstream at 6 km/hr and the river is traveling at 16 km/hr, then you are actually traveling at 10 km/hr.