Speed velocity and acceleration Physics 100 Chapter 2

Speed, velocity and acceleration Physics 100 Chapter 2

speed distance traveled speed = v = elapsed time Hawaii Kai Haleiwa In one hour 50 km v = 1 hr = 50 km/hr 50 km This is the average speed over 1 hour. For shorter time intervals it can be higher or lower.

Earth’s motion around the Sun r=1. 5 x 1011 m V = 2 pr 1 year distance elapsed time = 1011 m = 9. 4 x 8760 hrs = 11 m 2 x 3. 14 x 1. 5 x 10 = 365 days x 24 hrs/day 9. 4 x 1011 m 8. 76 x 103 hrs = 1. 1 x 105 km/hr = 1. 1 x 108 m/hr 70, 000 mi/hr

Velocity = speed + direction v 6 months later speed = same different direction r=1. 5 x 1011 m velocity is a “vector”: a quantity that has both magnitude and direction Length of the arrow = speed Direction of arrow same as direction of the motion

Scalars and Vectors Simple numbers: Number + direction Speed v Temperature T Velocity v relative positions r Force F Acceleration a r PSB Campus Center

Acceleration ( changes in v) change in velocity acceleration = elapsed time a = change in v elapsed time

Change in V = 100 km/hr Elapsed time = 3 sec a= change in v elapsed time 103 m = 100 km/hr = 33 km/hr s 3 s 3600 s =3. 6 x 103 s = 33 x 103 m 2 = 9. 1 m/s 3 3. 6 x 10 sxs “This baby goes from 0 to 100 km/hr in only 3 seconds”

Different ways to change V v v a Car speeds up v Car slows up v scree c h! a

Accelerations (continued) v v Car turn s a In all three cases, v changes. Therefore these are all examples of accelerations

Free Fall

t=0 5 m v 0=0 dist 5 m vavg = = = 5 m/s time 1 s 0 + v v + v 1 = v 1 1 = vavg = 0 2 2 2 v 1 = 2 vavg t=1 s = 10 m/s v 1=? V 1 = 10 m/s

Free-fall acceleration 10 m/s change in velocity acceleration = elapsed time 1 s 10 m/s ga = 1 s = 10 m/s 2 This is called the “acceleration due to gravity” and given the special symbol: g=10 m/s 2 Actually g=9. 8 m/s 2. But 10 m/s 2 is close enough for us.

Free fall from greater heights t = 0 s V 0 = 0 5 m 5 m t = 1 s V 1 = 10 m/s Total distance 15 m 20 m t = 2 s V 2 = 20 m/s 1 gt 2 2 25 m t = 3 s 45 m V 3 = 30 m/s 35 m t = 4 s V 4 = 40 m/s 80 m

Upward toss t = 4 s t = 3 s 80 m V 4 = 0 V 3 = 10 m/s 5 m 75 m 15 m t = 2 s Total height V 2 = 20 m/s 60 m v 0 t- 1 gt 2 25 m t = 1 s V 1 = 30 m/s 2 35 m t=0 V 0 = 40 m/s 0 m

Simple rule for free fall aka: projectile motion When Earth’s gravity is the only force involved: actual height = height for no gravity – ½gt 2

Horizontal toss t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s 5 m 20 m 45 m 80 m

upward toss t = 3 s t = 2 s 20 m t = 0 s t = 1 s 5 m 45 m t = 4 s 80 m

Shoot dead white communist the European monkey male

Shoot the DWEM: Slower bullet

Very fast horizontal toss t = 0 s V=8 km/s t = 1 s x= 8 km 5 m t = 2 s x=16 km 20 m t = 3 s x=24 km 45 m

Orbital motion is free fall

Artificial satellite

Turning car An object free to slide on the dashboard, tries to follow a straight line path