Motion, Speed, and Velocity Physics Motion, Speed, and Velocity

SC Standards Covered PS-5.1 PS – 5.2 PS – 5.6 Explain the relationship among distance, time, direction, and the velocity of an object PS – 5.2 Use the formula v=d/t to solve problems related to average speed or velocity PS – 5.6 Represent linear motion of objects on distance – time graphs

Motion When an object changes its position, motion has occurred. Distance- How far an object has moved. Displacement- How far an object has moved in relation to its starting point. Consider direction Example: Two runners travel along the same straight path in a straight line for 500 meters. At the end of the run their distances are the same but their displacements are different. How can this be so?

Speed- Distance an object travels per unit of time Relationships between speed, distance, and time: Speed = Distance/ Time = d/ t Constant Speed- speed does not change over time Average Speed- speed of motion when speed is changing Avg Speed = Total Distance/ Total Time Instantaneous Speed- speed at any given moment in time (speedometer)

Speed The units for speed: meters/second (m/sec) kilometers/hour (km/hr) Speed that does not change is constant speed

Graphing Motion Graph distance on the y-axis and time on the x-axis Slope = rise = distance = speed run time

Distance - Time Graph If something is not moving, a horizontal line is drawn. If something starts out slow and then speeds up, its change in speed can look like this.

Learning Checkpoint This graph shows several stages of motion: Stage 1: 100 m in 10 s Stage 2: 50 m in 10 s Stage 3: 150 m in 20 s Calculate the speed as indicated by each of the colors. Calculate the average speed. What is the total distance? What is the displacement?

Solution Stage 1: S= d/ t 100 m/ 10 s= 10 m/s Stage 2: S= d/t Ave Speed= Tot d/ Tot t 300 m/ 40 s= 7.5 m/s Distance = 300 meters Displacement = 0 meters

Velocity The speed and direction of an object’s motion. 88 km / hr southwest

Acceleration The change in velocity Acceleration is measured in m/sec/sec or m/sec2 Formula is: (final velocity - original velocity)/time

Deceleration vs. Acceleration A decrease in velocity is deceleration or negative acceleration A distance-time graph for acceleration is always a curve

Centripetal Acceleration Acceleration directed toward the center of circular path

Frames of Reference The object or point from which movement is determined Movement is relative to an object that appears stationary Earth is the most common frame of reference