Ch 5 Section 1 David Fan Mr. Chesbro P-2 I.
Measuring Motion A. Observing Motion 1. Detecting motion requires observing the object in relation to an apparently stationary object called a reference point 2. An object in motion changes position over time compared to a reference point. B. Common Reference Points 1. Earth’s surface, nonmoving objects (buildings, trees, mountains) 2. Moving objects can be used too; bird changing position in relation to a moving balloon. Earth moving around sun C. Speed Depends on Distance and Time 1. Speed is the rate at which an object moves (R=D/T) 2. SI unit for speed is meters per second (m/s) D. Determining Average Speed 1. Average speed= total distance / total time E. Recognizing Speed on a Graph 1. Distance traveled every hour is different F. Velocity: Direction Matters 1. Speed of an objection in a particular direction is velocity 2. Speed does not require a direction G. Velocity Changes as Speed or Direction Changes 1. Velocity is the rate of change of an object’s position 2. An object’s velocity is constant if its speed and direction don’t change. A bus changes velocity if direction or speed change H. Combining Velocities 1. If you sit down in a bus traveling 15 m/s east, you too are. But if you are walking down the aisle, you aren’t. 2. Resultant velocity is the sum of two velocities in same direction 3. To combine two velocities in opposite directions, subtract the smaller velocity from the larger velocity I. Acceleration: The Rate at Which Velocity Changes 1. Acceleration is just a change in rate, regardless of faster/slower J. Defining Acceleration 1. Acceleration is the rate at which velocity changes 2. To accelerate means to change velocity. Velocity changes if speed or direction changes 3. Acceleration is not just how much velocity changes, but also how fast. The faster velocity changes, the greater the acceleration is K. Calculating Acceleration 1. Acceleration= Final velocity – starting velocity/ time it takes to change velocity 2. If you have an acceleration of 1 m/s/s, your southward velocity increases by 1m/s.
L. Examples of Acceleration 1. Acceleration in which velocity increases is positive acceleration 2. Acceleration in which velocity decreases is deceleration 3. Velocity changes if your direction changes Example of Acceleration How Velocity Changes A plane taking off Increase in speed A car stopping at a stop sign Decrease in speed Jogging on a winding trail Change in direction Driving around a corner Change in direction Standing at Earth’s equator Change in direction M. Circular Motion: Continuous Acceleration 1. If you stand on the equator, you are traveling in a circle as the Earth rotates 2. An object traveling in a circular motion is always changing its direction 3. Since its velocity is always changing, acceleration is occurring 4. Acceleration in circular motion is centripetal acceleration N. Recognizing Acceleration on a Graph 1. Positive acceleration has a line that slopes upwards. Negative acceleration has a line that slopes downwards