Unit 2: Motion-- Speed and Velocity and Acceleration

1. Unit 2: Motion-- Speed and Velocity and Acceleration

2. What’s the difference between distance and displacement? • Distance: the total magnitude traveled (length without direction) • Displacement: the shortest distance from the starting point to the ending point • Position: where an object is, including direction, compared to where it was • Ladybug Example

3. What is speed? • Speed–The rate of change in distance with respect to time. • Non moving objects: speed = 0 m/s • Units: m/s, cm/s, mph • Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity.  • Scalar Quantities carry no direction information with them.

4. What is Velocity? • The rate of change in displacement with respect to time.  • Since displacement is a vector quantity, then velocity is also a vector quantity.  • v=d/t • v= velocity (m/s) • d= distance (m) • t= time (s) D T V

5. Speed & Velocity Examples • Speed is distance divided by time • 2 cm/s • Velocity includes the direction • 2 cm/s west West

6. What is the difference between average velocity and instantaneous velocity? • Average Velocity: The longer the time period measured, the more it leads to calculating an average velocity. • Instantaneous Velocity: The shorter the time period measured the closer it brings you to calculating an "instantaneous velocity".  Only if the time period becomes zero would we truly have an instantaneous velocity. 

7. Acceleration “Acceleration” occurs when your speed changes up or down (or when you change direction). • It is the rate speed changes • Level ground- no acceleration due to gravity • Steep down hill- acceleration due to gravity • Steeper hill= more acceleration • Deceleration is slowing down • Zero acceleration is at a constant speed AND not changing direction

8. Acceleration • Can use a graph to show acceleration • + slope = +acceleration (speed up) • - slope = - acceleration (slow down) • 0 slope = no acceleration • Acceleration= change in speed (cm/sec) time (sec) • a = vf-vi • t • Units: cm/sec*sec or cm/sec2

9. Free Fall- • Drop straight down • Acceleration due to gravity 9.8 m/sec2 • Terminal Velocity- • Highest velocity reached by a falling object • When an object stops accelerating, but continues to fall • When air resistance balances the pull of gravity

10. Projectiles • An object that is sent through the air is a projectile • The path of a projectile is called a trajectory • In the absence of air resistance, all objects fall with the same uniform acceleration = 10 m/s2 • Two objects of different sizes and weights, dropped from the same height, will hit the ground at the same time.

11. Resolving Vectors • To add vectors (going in same direction): line up tail to tip and add the numbers & keep the direction the same. • Ex: 4 m N + 3 m N = 7 m N • To subtract vectors (going in opposite directions): Subtract smaller # from larger # and keep direction of the larger #. • Ex: 15 m S - 3 m N = 12 m S • If the vectors are at right angles to each other, line up tail to tip and find the hypotenuse (Remember a2 + b2 = c2 and then solve for c) and combine the directions • Ex: 3 m N + 4 m E = 32 + 42 = c2 25 = c2 5 m NE = c