Describing Motion
Motion An object is in motion if its distance from another object is changing.
Reference Point 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
How does the description of an object’s position depend on a reference point? An object’s position is its in a certain from a reference point. distance direction Suppose your reference point changes… The description of the position will because the reference point is different, however the actual position change at all. change will not
Relative Motion Whether or not an object is in motion depends on the reference point.
To someone riding on a speeding train, others on the train don’t seem to be moving.
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Practice Test Answer
How would you describe your position? Distance and direction North Backward South East Left West Up Forward Right Down
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Displacement Vs distance
Distance vs Displacement The total length of the actual path from start to end. Displacement - Displacement is the length and direction of a straight line between starting and ending points. When would distance and displacement be the same? When an object moves in a straight line in one direction.
Distance and Displacement
Vector is a quantity that consists of both a magnitude and a direction. Usually represented on a graphic by arrows The length of the arrow represents magnitude Direction of arrow indicates direction of vector Must use vector addition to combine displacements
Combining Displacements Add the magnitudes of two displacement vectors that have the same direction. Two displacement vectors with opposite directions are subtracted from each other.
Combining displacements Vector addition is the combining of vector magnitudes and directions EX: 5km 10km 5 + 10= 15km 10km 3km 10 – 3= 7 km
Combining Displacements Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.
Combining Displacements Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.
Combining Displacements Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.
Combining Displacements Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.
Combining Displacements Measuring the resultant vector (the diagonal red line) shows that the displacement from the boy’s home to his school is two blocks less than the distance he actually traveled.
Vector Displacement is a vector, but distance is not. Point B Point A Point A
Assessment Questions A car is driving down the highway. From which frame of reference does it appear to not be moving? standing at the side of the road a car driving at the same speed but going the opposite direction sitting inside the car an airplane flying overhead
Assessment Questions A car is driving down the highway. From which frame of reference does it appear to not be moving? standing at the side of the road a car driving at the same speed but going the opposite direction sitting inside the car an airplane flying overhead ANS: C
Assessment Questions The metric unit of distance that would be most appropriate for measuring the distance between two cities is the meter. centimeter. kilometer. mile.
Assessment Questions The metric unit of distance that would be most appropriate for measuring the distance between two cities is the meter. centimeter. kilometer. mile. ANS: C
If you walk across town, taking many turns, your displacement is the Assessment Questions If you walk across town, taking many turns, your displacement is the total distance that you traveled. distance and direction of a straight line from your starting point to your ending point. distance in a straight line from your starting point to your ending point. direction from your starting point to your ending point.
If you walk across town, taking many turns, your displacement is the Assessment Questions If you walk across town, taking many turns, your displacement is the total distance that you traveled. distance and direction of a straight line from your starting point to your ending point. distance in a straight line from your starting point to your ending point. direction from your starting point to your ending point. ANS: B
Assessment Questions You travel 30 miles west of your home and then turn around and start going back home. After traveling 10 miles east, what is your displacement from your home? 20 km 20 km west 40 km 40 km west
Assessment Questions You travel 30 miles west of your home and then turn around and start going back home. After traveling 10 miles east, what is your displacement from your home? 20 km 20 km west 40 km 40 km west ANS: B