When is an object in motion, and how can you calculate speed?

How do you know when an object is in motion?

Science Standard 8.1.a: Students know position is defined in relation to some choice of a standard reference point and a set of reference directions. Science Standard 8.1.b: Students know that average speed is the total distance traveled divided by the total time elapsed and that the speed of an object along the path traveled can vary.

Science Standard 8.1.c: Students know how to solve problems involving distance, time, and average speed. Science Standard 8.1.d: Students know the velocity of an object must be described by specifying both the direction and the speed of the object.

motion: an object is in motion if its distance from another object is changing. reference point: a place or object used for comparison to determine if something is in motion. distance: the length of a path between two points. displacement: the length and direction that an object has moved from it starting point. vector: a quantity that consists of both a magnitude and a direction.

speed: the distance an object travels per unit of time. average speed: divide the total distance traveled by the total time. instantaneous speed: the rate at which an object is moving at a given instant in time. velocity: speed in a given direction. slope: steepness of a line on a graph.

Relative Motion An object is in motion if it changes position relative to a reference point. Whether or not an object is in motion depends on the reference point you choose.

Relative Motion Distance is the total length of the actual path between two points. Displacement is the length and direction of a straight line between starting and ending points.

Distance & Displacement

Calculating Speed To calculate the speed of an object, divide the distance an object travels by the amount of time it takes to travel that distance Speed = Distance Time

Calculating Speed If a distance runner runs 10 miles in one hour, what is her speed. Speed = Distance Time Speed = 10 miles = 10 mph (miles per hour) 1 hour

Calculating Average Speed To calculate average speed (v), divide the total distance traveled (d) by the total time (t). Average Speed = Total Distance Total Time

Calculating Average Speed A cyclist travels 32 kilometers during the first 2 hours. Then he travels 13 kilometers during the next hour. What is his average speed? Average Speed = Total Distance Total Time v= 32 km + 13 km = 45 km 2 h + 1 h = 3 h v= 15 km/h

Calculating Velocity Changes in velocity may be due to changes in speed, changes in direction, or both. Like displacement, velocity is a vector. It has magnitude and direction. A jet airplane’s velocity could be described as 700 miles per hour to the east.

Graphing Speed The slope of a distance-versus-time graph represents speed, that is, the rate that distance changes in relation to time. Time is shown on the horizontal, or x-axis. Distance, or position, is shown on the vertical, or y- axis. A point on the line represents the distance an object has traveled from the origin or a reference point at a particular time.

Graphing Motion You can use distance-versus-time graphs to interpret motion.

HOMEWORK CONNECTION  Read pages in your Science textbook.  Complete the Section 9-1/9-2 Review & Reinforce  Write a detailed SUMMARY of the section and complete the UNANSWERED QUESTIONS section of your notes.  Choose two of the remaining Depth & Complexity ICONS in your notes and explain how they relate to this section.