Motion Intro with Tim and Moby Intro with Tim and Moby

Describing Motion Whether or not an object is in motion depends on the reference point you choose. Reference point (Frame of reference): background used to tell if an object is moving(Frame of reference)

Average Speed Speed is the rate at which an object moves. To find speed you need two bits of information Total Distance the object moves Total Time it takes to move that distance

Calculating average speed Formula for speed Key: s = speed d = distance t = time

Calculating Speed (a.k.a Average speed) A car travels 150 kilometers in 3 hours. What is the average* speed of the car? Formula: Substitutions: Answer (with units!): –*average means the car goes slower sometimes, faster sometimes, and may even stop during the trip

Velocity Speed in a given direction –Mostly used for airplanes to include direction and speed –“450 km/hr NORTH” –Example: Storm movements to know how fast and what direction they travel “storm moving at 10 km per hour from the west” Velocity video clipVelocity

Acceleration The rate at which speed changes –“–“How fast is the speed changing?” Acceleration is a change in speed –P–Positive acceleration is an increase in speed –N–Negative acceleration is a decrease in speed (deceleration)

Calculating Acceleration To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time. Starting velocity V s Final velocity V f

Calculating Acceleration a = v f – v s t a = acceleration v f = final or ending speed v s = starting speed t = time Acceleration = Final Velocity – Starting velocity time Acceleration is always expressed in units with velocity (ex. Meters per second, km/hr, etc.) over time (seconds, minutes,etc). Acceleration is the change in velocity over a period of time

An airplane takes off down the runway. It started at 0 m/s and accelerated to 24 m/s in 3.0 seconds time. How fast did it accelerate? What information is given? Starting (initial) velocity of 0 m/s Final velocity of 24 m/s Time of 3.0 seconds What is being asked? Find the acceleration. What formula will solve this? a = Final – starting time a = 24 m/s – 0 m/s 3.0 s a = 24 m/s 3.0 s a = 8 m/s or 8 m/s/s or 8 m/s 2 s

What is being asked? –Find the acceleration. What formula will solve this? a = v final – v starting t a = 18m/s – 4 m/s 2.0 s a = 14 m/s 2.0 s a = 7 m/s or 7 m/s/s or 7m/s 2 s What information is given? Starting (initial) velocity of 4 m/s Final velocity of 18m/s Time of 2.0 seconds A roller coaster accelerates from 4 m/s to 18 m/s in 2 seconds. How fast did it accelerate?

Negative Acceleration (Deceleration) The same roller coaster comes back into the start house and stops. If it started at 18 kilometers per hour and took 6 seconds to come to a complete stop, what is its acceleration? Formula: Substitutions: Answer (with units!):

Gravity accelerates all objects towards the Earth at the same rate (9.8 meters per second per second) (that’s 32 feet per second per second) Free Fall: the only force acting on an object is gravity as it accelerates towards earth Gravity and acceleration

Air resistance Opposing force of air on an object –A type of friction Also known as “drag” or air friction Terminal Velocity: the greatest velocity a falling object can reach due to drag free fall down = air resistance upward Mythbusters:Feather and Hammer video An elephant and feather fall at the same rate (9.8 m/s/s) with no air friction With air resistance:

Summary How fast = velocity. How far = distance. How quickly “how fast” changes = acceleration