# PHY 125 – Lecture 5 – Instant Velocity, Average velocity and Acceleration

Published on: Thu Feb 04 2010

When an object is traveling at a constant velocity, it is special. It’s **Instantaneous Velocity** and **Average Velocity**are the same, and the position of the object can be stated by:
Read this: *“The position of the object is at point x which is equal to the origin position plus Velocity times Time.”*
The slope between two positions of the object tells us the average velocity. Slope can be in meters per second or seconds per meter, but it should have a unit attached to it, in the form of Unit per Unit. On a graph of velocity, time would occupy the x axis, and position would occupy the y axis.
**Instantaneous Velocity** can be thought of as constant velocity between two very close positions. So this starts to get into Calculus, which I need to review, but expressing Instantaneous Velocity is really just the same as average velocity as the x axis approaches 0. (Since x is Time, as the time is shorter the closer you are to an instant)
**Acceleration** tells you about how fast the velocity of an object is changing. There is also an Average and Instantaneous Acceleration. When speaking about acceleration, velocity is along the x axis and Time and along the y axis. The basic formula is the same as velocity, with the only difference the axis of the graphs.
The second half of the class the Professor spoke about some special equations for objects with a ** constant acceleration**. You can use these to get the Average Velocity or The Position or Time, depending on what you have to work with!
x = position
v = velocity
t = time
a = Constant Acceleration
**A note on Speed:**
Speed is the same as velocity, but it does not tell about direction! A car going -30mph is traveling at a speed of 30 miles per hour somewhere, but a car at a velocity of -30mph is going in reverse at a speed of 30 miles per hour.