Physics Physics: The study of forces, motion and energy Motion: Change in position over time compared to a reference point Reference Point: object used to determine motion or position of an object ( can be non-moving or other moving objects) Speed: Distance an object travels over a certain time period Formula: speed = distance time Common Units = Miles = mi/hr or mph, kilometers = km/hr, meters = m/s hour hour second Common Speeds: Kangaroo: 15 m/s Cheetah: 27 m/s sound: 343 m/s light: 3 million m/s

Speed: 2 ways to describe speed: Instantaneous speed: Speed at any given moment Police officer clocks a car going 85 miles per hour, the officer has measured the car’s instantaneous speed. A car’s speedometer also measures instantaneous speed. Average Speed: Total distance traveled divided by the total time. Most objects do not travel at a constant speed. Example: Suppose a cheetah ran 270meters in 10 seconds. What is his average speed? Average speed = 270m/10s = 27 m/s Velocity: Speed in a given direction Formula = Distance (with direction) Time Examples: 7 mph south 35 m/s west 85 km/hr north

Acceleration How quickly speed or velocity changes Occurs when an object speeds up, slows down (decelerates) or changes directions Formula = final velocity – Initial velocity time it took to change velocity Common units= m/s/s, mi/hr/s, km/hr/s Example 1: A car can travel from 0 mph to 60 mph is 3 seconds, what is its acceleration? Acceleration= 0 mph –60mph = - 60mph = -20mph 3 s 3 s s Example 2 : A car was traveling at 60 mph and stopped in 3 seconds. What was the car’s acceleration? Acceleration= 60 mph – 0mph = 60mph = 20mph 3 s 3 s s