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## Chapter 2 Displacement and Velocity

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**Frame of Reference**- In order to measure the distance of an object we must use a frame of reference. Point A --------> Point B - These are usually distinct points on the Earth's surface or distinguishing points in the sky.**The perception of motion depends on the observer’s frame**of reference • Describe the motion observed by one of the boys in the drawing, how does the motion appear to be different to the other boy?**The perception of motion depends on the observer’s frame**of reference • Imagine you are the girl observing the bus, describe the motion of each object that you can see**Distance is a scalar quantity and tells you only the**magnitude (number sum only) of a path taken.**Displacement is the shortest distance between the starting**point and the end point.**You drive the path, and your odometer goes up by 8 miles**(your distance). Your displacement is the shorter directed distance from start to stop (yellow arrow). What if you drove in a circle? Distance vs. Displacement start stop**Speed is the distance traveled**by a moving object over a period of time**Constant speed**• A moving object that doesn’t change it’s speed travels at constant speed • Constant speed means equal distances are covered in an equal amount of time**Calculating Speed**• Speed = Distance Time • If a runner travels 100 m in 10 seconds what was his average speed? • Probably not constant • Can solve for the other pieces too • Distance = speed x time • Time = Distance Speed**Velocity is speed in**a given direction**instantaneous velocity - the velocity that something has at**any one instance • (The terms instantaneous speed and avg. speed may also be used)**The average velocity for a trip might be 53 miles/hour.**However, during this trip your instantaneous speed might have been 0 miles/hour at a stoplight or 70 miles/hour on the open road.