Velocity + Acceleration

SI units  SI units needed  Time = seconds (s)  Other common units are the minute, hour, microsecond and nanosecond  Distance = meters (m)  Other common units are the centimeter, millimeter, kilometer, nanometer and picometer

Distance vs. Displacement  Distance is equal to the total amount of space something moved  Displacement is the space moved from the initial position.

Speed  Lunar recession = 1.3x10-9  Snail= 1x10-6  Man = 10m/s  Cheetah = 30 m/s  Sound at S.L. = 340 m/s  M-16 bullet= 975m/s  SR-71 Blackbird = 981m/s  Apollo =11082 m/s *record  Earth orbit = m/s  Solar system orbit = 2x10 5 m/s  Light= 3x10 8 m/s  Speed: Rate of change in position or how fast something is going  Given in distance per unit of time  m/s km/h mph  In physics magnitude of velocity vector  Average speed – total distance/ total time  95 miles in 1:20 What is the average speed?

Instant speed  Instantaneous speed – speed at an exact moment in time – speedometer in a car  Constant speed – objects with no variation in speed – vehicles rarely travel at constant speeds

Velocity  Calculating speed: s = d/t  Velocity : speed and direction of something  V=d/t  2 people traveling at 60 km/h in different directions don’t have the same velocity  Thought Question: Does constant speed necessarily imply constant velocity?

Calcultions  You travel from Mandan to Fargo in your ‘87 Oldsmobuick, the trip of 210 miles takes you 2 hours 40 minutes. What was your average velocity.  How long would it take you to travel to Minneapolis 66O km if you drove at 115 km/h. How far is the nearest star if it takes you 2.7 years traveling at the speed of light to reach it.

Problems  Speed and velocity are often used interchangeably but it is important to remember that velocity implies a direction of travel. This is especially important when it comes to the forces and energy that cause changes in motion.

Graphing  urces/bu_semester1/c2_twocars_graphs.html urces/bu_semester1/c2_twocars_graphs.html  What do the slopes of each graph represent?

Acceleration  Acceleration is the change in velocity over time. Constant speed does not imply constant velocity  Positive acceleration- Acceleration in the same direction as velocity  Negative acceleration- acceleration in the opposite direction of velocity

Acceleration  How many ways can you accelerate in your car?  1.  2.  3.  So your car has 3 accelerators  Calculate acceleration : 

Acceleration formulas  To calculate acceleration  Calculate the change in velocity and divide by the change in time.  a =( final velocity – initial velocity) / time for the change to take place  a= vf – vi/t or a =  v /t

Acceleration Problem  If you drop a penny off of the Empire State Building and it reaches a speed of 29.4m/s after 3 seconds, what is its average acceleration?  How long would the penny have to fall to reach a speed of 100m/s?