CALCULATING SPEED AND ACCELERATION Chapter 11

Speed  Speed = distance/time  Velocity is speed with direction!  When an object covers equal distances in equal amounts of time, it is moving at a constant speed.  Instantaneous speed: speed at a given time  Car Speedometer

Acceleration  Acceleration = (final velocity – initial velocity) time  What is true of an object’s acceleration if it is moving in a circle at a constant speed (no change in speed)? Why?  An object is moving with a constant velocity. What is the objects acceleration?

Calculating Speed  To calculate speed, you must measure two quantities : the distance traveled and the time it took to travel that distance.  Average Speed:  SI unit for speed: meters per second (m/s)

Calculating Speed EquationGives you…If you know…. v = d/tspeed distance and time d = v x tdistancespeed and time t = d/vtimedistance and speed

Let’s Practice!!!  Find the velocity in meters per second of a swimmer who swims 110 m toward the shore in 72 s. Looking for:Solution: Given: Relationship:

Let’s Practice!  A train travels 225 kilometers in 2.5 hours. What is the train’s average speed? Looking for:Solution: Given: Relationship:

You Try It!  An airplane travels 3,260 kilometers in 4 hours. What is the airplane’s average speed?  A person in a kayak paddles down river at an average speed of 10 km/h. After 3.25 hours, how far has she traveled?

Calculating Acceleration  To calculate acceleration, you must measure three quantities: the initial velocity, final velocity and time it took to change velocities.  Average Acceleration:  SI unit for Acceleration: meter per second per second (m/s^2)  NOTE: Rest in word problems => v = 0 m/s (could be final or initial depending on situation)

Calculating Speed EquationGives you…If you know…. a =(Δv) t acceleration Initial and Final v Time Final v = (a x t) + initial vFinal v Acceleration Initial Velocity Time Initial v = final v – (a x t)Initial v Acceleration Final velocity Time t = Δ v/aTimeInitial and Final v acceleration

Let’s Practice!!!  Bob is at a stop light and then speeds up to 60 miles/hr. It takes Bob 1 hour to go from rest to 60 miles/hr. What is his acceleration? Looking for:Solution: Given: Relationship:

Mr. Terrell drops (starts from rest) a water balloon from the top of a building onto a football player at the ball game. If the acceleration is -9.8 m/s 2 and it takes the 10 s to reach the football player, what is the final velocity of the balloon? Looking for:Solution: Given: Relationship:

James while on his skateboard experiences a constant acceleration of 1 m/s 2 for 2 seconds until he reaches a speed of 20 m/s. What is his initial velocity? Looking for:Solution: Given: Relationship:

A ball experiences an acceleration of -3 m/s 2. It goes from 30 m/s to 14 m/s. How long does it take the ball to slow down? Looking for:Solution: Given: Relationship:

You Try It!  A skater goes from a standstill to a speed of 6.7 m/s in 12 seconds. What is the acceleration of the skater?  During a race, a sprinter increases from 5.0 m/s to 7.5 m/s over a period of 1.25s. What is the sprinter’s average acceleration during this period?

Graphing Review  Describe the following graphs: Distance (m/s) Time (s) abcd Speed (m/s) Time (s) abcd

Finding Slope Example  Slope from seconds?  Slope from 5 – 10 seconds?

Units of slope on a position vs. time graph? SLOPE (on position vs. time graph) = ____________ Units of slope on a speed vs. time graph? SLOPE (on velocity vs. time graph) = _____________

Exit Slip  You ride your bike for a distance of 30 km. You travel at a speed of 0.75 km/ minute. How many minutes does this take?

Warm-Up  Calculate the distance a plane flies on an 8 hour flight from Chicago to London. Assume a constant speed of 800 km/h. Looking for:Solution: Given: Relationship: