Speed, Velocity, and Acceleration Motion Speed, Velocity, and Acceleration

Frames of Reference The object or point from which movement is determined An object is in motion if its position changes relative to another object Movement is relative to an object that appears stationary Earth is the most common frame of reference

Questions How do you determine if an object is in motion? If it changes position with respect to a reference point. Why are reference points that are stationary best to use? If the reference point is moving, it is difficult to determine in what direction the object is moving, or if moving at all

Motion Motion is a change in position relative to a frame of reference Speed is the distance traveled in a given amount of time Speed=distance time

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

Solve these speed problems: If a cyclist is traveling at a constant speed of 10m/s, how long does it take her to travel 400 meters? Speed= distance convert to time = distance __________ __________ time speed 400 m ______ = 40 s 10 m/s

Average speed Total distance divided by the total time Formula:

Solve these average problems: Leg 1 Swimming Total distance: 3.0 km Triathlete A’s total time: 0.8 h Triathlete B’s total time: 1.0 h Triathlete A’s average speed?? Triathlete B’s average speed?? Triathlete A= 3.8 km/h Triathlete B= 3.0 km/h

Leg 2 Biking Total distance: 50.0 km Triathlete A’s total time: 3.0 h Triathlete B’s total time: 2.5 h Triathlete A’s average speed? Triathlete B’s average speed? Triathlete A= 16.7 km/h Triathlete B = 20.0 km/h

Leg 3 Running Total distance = 12.0 km Triathlete A’s total time = 1.2 h Triathlete B’s total time = 1.0 h What was total distance of all 3 legs? Triathlete A’s total time? Triathlete A’s average speed? Triathlete B’s total time? Total distance= 3.0 km + 50.0 km + 12.0 km = 65.0 km Triathlete A’s total time = .8 h + 3.0 h + 1.2 h = 5.0 h Triathlete A’s average speed = 65.0 km/5.0 h = 13 km/h Triathlete B’s total time = 1.0 h + 2.5 h + 1.0 h = 4.5 h Triathlete B’s average speed = 65.0 km/4.5 h = 14.4 km/h

Velocity Speed in a given direction When you know both the speed and direction of an object’s motion, you know the velocity Velocities in the same direction combine by adding Velocities in different directions combine by subtracting

Questions How is velocity different from speed? Which two factors determine an object’s velocity?

How do you graph motion? You use distance vs time graphs Time is shown on x-axis; distance is shown on y-axis The steepness of a line on a graph is called slope (slope = rise/run) You can tell how fast or slow something is traveling by the steepness of the slope.

Acceleration The change in velocity (increasing speed, decreasing speed or changing direction) 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

Questions What is acceleration? What is the shape of a distance-time graph for acceleration?