Frame of Reference Demo Stand at the front of the room turned sideways and toss an object up into the air and catch it. Ask students to describe the path of the ball (should say it goes up then down). Tell them that to you it also appears to be going up and down. Now slowly walk across the classroom and toss the object as you do. Ask the students to describe the path of the object. They should say that the ball is traveling at an arc forward. But to you the ball appears to simply be going up and down…same as before. Elaborate that the description of motion depends on the frame of reference.

Bell-Ringer Frame of Reference Probably Means Frame of Reference Actually Means

Distance and Displacement Ch. 11.1

Motion Before you can discuss distance and displacement you have to understand motion. To describe motion you must state both direction and speed of an object You must also tell its location at a certain time

Frame of Reference Frame of Reference – a system of objects that are not moving with respect to one another. To describe motion accurately and completely, a frame of reference is necessary. Think about this: If you are riding a train and look at the other passengers do they appear to be moving? How about to someone on a platform watching the train pass by?

Relative Motion How fast the passengers on a train are moving depends on the frame of reference chosen to measure their motion. Relative Motion – movement in relation to a frame of reference As the train moves past a platform, people standing on the platform will see those on the train speeding by. When the people on the train look at one another, they don’t seem to be moving at all. https://www.youtube.com/watch?v=oWgyye8YVzc

Measuring Distance Distance – the complete length of a path between two points. When an object moves in a straight line, the distance is the length of the line connecting the object’s starting point and end point. What is the distance traveled by the boy from his home to school?

Measuring Displacement Displacement – the direction from the starting point and the length of a straight line from the starting point to the ending point. Displacement describes and object’s position relative to a given point.

Vectors To add displacements we use vector addition. Vector – a quantity that has magnitude and direction Magnitude can be: size, length, or amount

Displacement Along a Straight Line When two displacements, represented by two vectors, have the same direction, you can add their magnitudes. If two displacements are in opposite directions, the magnitudes subtract from each other.

Combining Displacements The magnitude of the two displacement vectors have to same direction so you ADD them. What is the displacement for scenario A?

Combining Displacements The magnitude of the two displacement vectors have opposite direction so you SUBTRACT them. What is the displacement for scenario B?

Combining Displacements The vector sum of two or more vectors is known as the resultant vector. The resultant vector points directly from the starting point to the ending point. The resultant vector is depicted by the red line.