Frame of Reference, Speed, Velocity, Acceleration Motion Frame of Reference, Speed, Velocity, Acceleration

Motion Motion = change in position relative to a frame of reference Something assumed to be stationary Used to judge motion

Ways to measure motion: Distance = how much change in position (key words….how far) Time = how long it took (key words….how long) Speed = how much distance is covered per unit of time (key words…..how fast) Direction = N, S, E, W, Up, Down

Calculating Speed: Speed = distance per unit of time …..so Time = distance/speed Distance = speed * time Units = cm/s m/s mi/hr km/hr

Average Speed for a trip DO NOT add all the speeds and devide by how many there are!!!!!!! DO total distance/ total time (yes it will come out differently) Try….. Use average speed = total distance total time

Calculate the average speed for the entire trip Leg of Trip Time (hours) Distance covered (km) Speed for that Leg of the Trip (km/hr) First leg 2 150 Second leg 3 300 Layover 1 Third leg 4 200

Average speed = 650km/10hrs = 65km/hr NOT: (75 + 100 + 0 + 50 =225/4 = 56.25km/hr) Leg of Trip Time (hours) Distance covered (km) Speed for that Leg of the Trip (km/hr) First leg 2 150 150/2 = 75 Second leg 3 300 300/3 = 100 Layover 1 Third leg 4 200 200/4 = 50 totals 10 650 650/10 = 65

Constant Speed Speed stays the same Graph of distance vs. time is a straight line

Horizontal lines show… No change in position so no distance covered but… Time is passing so the object is… Standing still speed = 0

Steeper lines show…. More distance covered per unit of time so.. faster speed. A = slow B = stand still C = fast

Slope of distance time graph Slope = rise so slope = distance run time distance = m so is speed time S Fast speed = more distance in same time or same distance in less time

Position vs. Time have Negative slopes Negative slope means you are coming back toward the starting point.

Velocity = speed in a direction 25 m/s is a speed 25 m/s West is a velocity Constant velocity = speed and direction stay the same. If you go 50 mph around a race track.. Is this constant speed? Is this constant velocity?

Velocities can be combined Velocities in same direction …. add Velocities in opposite direction…. subtract

Acceleration How quickly speed changes + acceleration = increasing speed - acceleration = decreasing speed Acceleration = change in speed/time

Calculating Acceleration Vi = initial velocity (starting speed) Vf = final velocity (ending speed) t = time it took for the speed to change a = Vf-Vi t

Graphing Acceleration