PhysicsPhysics: 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/sCheetah: 27 m/ssound: 343 m/slight: 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 south35 m/s west85 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