Matter in Motion Motion may be described, measured and predicted.

Measuring Motion Name something in motion that you cannot see moving? You cannot see Earth moving. Yet, we know it moves (revolves) around the sun

A. Observing Motion by Using a Reference Point An object in motion is moving in relation to an object that appears to stay in place. You can use – north, south, east, west, up or down- to describe the direction of an objects motion. -This is called a reference point. The surface of Earth is a common reference point.

B. Speed’s Dependence on Distance and Time The speed of an object depends on the distance traveled and the ______ taken to travel that distance. The motion of any object can be described by The SI unit for speed is ____________________ time - And speed -Direction of motion -The objects position (m/s) meters per second.

1. Determining Average Speed total distance Average speed = total time Average speed is useful because objects do not travel at a constant speed.

When driving a long distance over 4 hrs the distance and speed traveled each hour will be different. (Due to weather, traffic, etc…) What would the average speed be for a 360 km trip over a period of 4 hrs? 360 km Average speed = = 4 h 90 km/h

Velocity: Direction Matters The speed of an object in a particular direction. Example: speed = 600km/h velocity = 600km/h south

Changing and Combining Velocity Constant velocity = no change in speed or direction Changing velocity = a speed or direction change Velocity is combined when an object is moving in/on another moving object. – Objects moving in the same direction – add velocities – Objects moving in opposite directions – subtract velocities

Acceleration An object accelerates if its speed, direction, or both change. Positive acceleration = increase in velocity Negative acceleration = decrease in velocity Acceleration depends on how much as well as how fast velocity changes.

Calculating Average Acceleration final velocity - starting velocity Average acceleration = time it takes to change velocity Acceleration is expressed in Example: 5 m/s – 1 m/s Average acceleration = = 1 m/s 2 south 4 s m/s 2

Did acceleration occur? You are riding your bike at 9km/h. Ten minutes later, your speed is 6km/h. You ride your bike around the block at a constant speed of 11 km/h. You ride your bike in a straight line at a constant speed of 10km/h. Yes, speed decreased Yes, direction changed No, speed nor direction changed.

On a graph: – positive acceleration will show a line that moves upward – Negative acceleration will show a line that moves downward An object traveling in a circular motion is always changing direction = velocity is always changing and the object is accelerating. Centripetal acceleration: acceleration in a circular motion. – Example: Ferris wheel, windmill, moon’s orbit