MOTION MOTION Motion is the change in an

MOTION

MOTION • Motion is the change in an object’s position (or location) relative to a reference point. • A reference point is an object that appears to stay in place. • Sometimes the change in distance from a reference point to an object can be measured. • That would make the motion of the object quantifiable. • Quantifiable: able to measured in numbers.

SPEED • Speed is the distance traveled divided by the time interval during which the motion occurred. • Speed = Distance ÷ Time • Speed Units are always (Distance Units) ÷ (Time Units) • Miles/Hour (Mph), Feet/Second (fps), Kilometers/Hour (Kph) • Speed is always positive. • Speed does not include a direction. • This makes speed a SCALAR quantity • A SCALAR quantity is described only by a numerical value.

AVERAGE SPEED • Most objects do not travel at a constant speed • When you are walking somewhere you will change speeds often due to many different factors, terrain, obstacles, distractions, etc. • When driving or riding in a car or other vehicle your speed will also vary due to these different factors. • This makes calculating the average speed a very useful tool. • Average Speed = Total Distance ÷ Total Time

AVERAGE SPEED VS INSTANTANEOUS SPEED • Average speed is an average that can only be measured by using the formula Total Distance ÷ Total Time • Instantaneous speed is a measurement of the actual speed something is moving in “that moment” or “that instant” • Instantaneous speed is measured by using instruments like speedometers or radar guns.

SAMPLE AVERAGE SPEED PROBLEMS • A quarterback can throw a football 40 meters. It takes the ball 2 seconds to travel that distance. What is the Average Speed in Meters per Second? • Now the quarterback throws the ball 40 meters in 2 seconds and then the ball is intercepted and runback 10 meters in another 2 seconds. What is the average speed of the ball now?

DISTANCE VS TIME ON A GRAPH

VELOCITY • • • Velocity is the speed of an object in a specific direction. Velocity is a VECTOR quantity. This means that velocity is described using a numerical value and a direction. Velocity can be negative or positive. Velocity units are the same as speed units only with a direction added in. Mph north, Kilometers per hour south, fps up, meters per second down, etc. • An objects velocity will change if either its speed or its direction changes.

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ACCLERATION • Acceleration is the rate at which velocity changes. • Acceleration occurs if an object’s speed, direction, or both its speed and direction change. • Acceleration can be positive or negative. • When an object’s velocity increases it is considered to be a positive acceleration. • When an object’s velocity decreases it is considered to be a negative acceleration or deceleration. • Acceleration is also a measure of how fast an object’s velocity changes. • The faster an object’s velocity changes the greater the acceleration is.

CALCULATING ACCELERATION •

MORE PRACTICE • A runner finishes the last stretch of a race in 4 seconds. During that time the runner sped up from 5 m/s to 9 m/s. What was the runners acceleration during the last stretch of the race? • After crossing the finish line the same runner takes five seconds to come to a complete stop. What is the acceleration of the runner from the time he crossed the finish line until he came to a complete stop?