Speed Velocity CMS Georgia Davis Speed Speed is

Speed & Velocity CMS Georgia Davis

Speed • Speed is the rate at which an object moves. • To calculate speed you must know the distance and time • The equation for speed is: speed = distance/ time or s = d/t • For example: a cyclist might travel 30 kilometers in 1 hour or 30 km/h • We read the product as 30 kilometers “per” hour.

1. Suppose you walk 10 m down a hallway in 2. 5 s. What is your average speed? Answer: 4 m/s

Average Speed • The speed of most moving objects is not constant. • To calculate average speed we use the equation: Average speed = total distance/ total time • Example: Total distance = 32 km + 13 km Total time = 2 h + 1 h Average speed = 45/3 = 15 km/h

Graphing Speed • Suppose you watched a dog walk beside a fence. • A graph can show the total distance walked in 10 seconds. • The line will not be straight because dogs do not walk at a constant speed.

What is the average speed of the dog? 8 Dog Walk 7 Distance (m) 6 5 4 Series 1 3 2 1 0 1 2 3 4 5 6 Time (s) 7 8 9 10 11

Velocity • Two birds leave the same tree at the same time. They both fly 10 km/h for 5 min but do not end up in the same place. Why not? • They flew in different directions. Both had different velocities. • Velocity is speed plus direction.

Changing Velocity • Velocity changes when speed changes, direction changes, or both changes. Situation What Changes Raindrop falling faster and faster speed Runner going around a turn on a track Car taking an exit off a highway Train arriving at a station Car stopping at a traffic light Baseball caught by catcher Baseball hit by a batter speed & direction

Acceleration • Acceleration is the rate at which velocity changes. • Therefore an object accelerates if the speed (increase or decrease), direction, or both changes.

• An increase in speed is referred to as positive acceleration. • A decrease in speed is referred to as negative acceleration or DECELERATION. • An object traveling at a constant speed accelerates if it changes direction.

Accelerating? • • • Car traveling at constant speed of 65 mi/h. Runner rounding a turn. Baseball pitched. Stopping for school bus. Swerving to miss a dog in road. Riding the Ferris wheel at the county fair.

Calculating Acceleration • Acceleration = Final speed – Initial speed Time Speed’s unit is m/s & time’s unit is seconds. Acceleration is change in speed/ time, therefore the unit is m/s/s or just m/s 2

You try… • An airplane accelerates on a runway to 40 m/s after 5 seconds. What is the acceleration?

• As a roller coaster car starts down a slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its speed is 22 m/s. What is its average acceleration? • 22 m/s - 4 m/s 3 s • 18/3 = 6 m/s 2

Slope =Rise/Run 4 m/s 2 s = 2 m/s 2

Fill in the graphic organizer for a car that starts from one stop sign and approaches the next stop sign. Use the following terms: velocity, positive acceleration, deceleration, and at rest.