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Distance and Displacement. Physical Science Unit 2. Frame of Reference. To describe motion accurately and completely, a frame of reference is necessary f rame of reference is a system of objects that are not moving with respect to one another.
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Distance and Displacement Physical Science Unit 2
Frame of Reference • To describe motion accurately and completely, a frame of reference is necessary • frame of reference is a system of objects that are not moving with respect to one another. • Ex. A butterfly flying up and down in front of a person • Relative motion is movement in relation to a frame of reference. • Ex. A car driving by someone standing on the side of the road
Measuring Distance • Distance is the length of a path between two points. (only numerical) • Distance from Madison to Flowood (not a straight line) • The SI unit for measure distance is meter (m) • For larger measurements of distance the kilometer (km) is used.
Measuring Displacement • To describe an object’s position relative to a given point, you need to know how far away and in what direction the object is from that point. • Displacement is the direction from the starting point and the length of a straight line from the starting point to ending point (straight line distance). • Numerical value and a direction
Vectors • Displacement is an example of a vector • Vectors are quantities that have magnitude and direction. • The magnitude can be size, length, or amount • Vector addition is the combining of vector magnitudes and directions
Displacement Along a Straight Line • When two displacements represented by two vectors, have the same direction, you can add their magnitudes.
Continued….. • When two displacements are in opposite directions, the magnitudes subtract from each other
Questions • What is a frame of reference? How is it used to measure motion? • How are distance and displacement similar and different? • How are displacements combined? • A girl who is watching a plane fly tells her friend that the plane isn’t moving at all. Describe a frame of reference in which the girl’s description would be true. • Is displacement more like the length of a rope that is pulled tight or the length of a coiled rope? Explain
Questions • Would you measure the height of a building in meters? Explain your reasoning. • Should your directions to a friend for traveling from one city to another include displacements or distances? Explain • The resultant vector of two particular displacement vectors does not equal the sum of the magnitudes of the individual vectors. Describe the directions of the two vectors