Speed Velocity and Acceleration An Interactive Power Point

Speed, Velocity, and Acceleration An Interactive Power Point

Speed • To calculate speed use the equation: Speed = distance time Speed only gives distance and time

Speed Units • • m/s km/s m/h km/h • When you read the first unit, you say meters “PER” second. • Do not write mps

Average Speed • On a trip from Chicago to Texas could you stay the same speed? • You could get an average of all the speeds during the trip.

How do we calculate average speed? • The total distance of the trip divided by the total time of travel.

Magic Triangle • This triangle tells you the formulas you need for speed, distance, and time • s = d t • d = s x t • t = d s

Speed Problems • A baseball moves 11 m in 1 sec. What is its speed? • Speed = distance time • A car travels 70 km in 1. 75 h (hours). What is its speed? • S = D T

Speed is Relative! • What does it mean when we say that a car moves at a rate of 80 km/h? • What do we mean that it is relative to? • Unless the problem says something else, the motion that we discuss is ALWAYS relative to Earth.

What is Velocity? • Describes the motion and the direction. • Even if speed remains the same, if the direction changes then the velocity has changed.

Follow the steps to solve an equation. • Problem: You walk 5 meters in 3 seconds. What is your velocity? • Step 1: Write what you know. d = 5 meters t = 3 seconds v = ? • Step 2: Write the formula you will use. v = d / t • Step 3: Put the numbers in for the variables that you know. v = 5 meters 3 seconds • Step 4: Do the math. v = 1. 6667 meters/seconds = 1. 7 m/s Your velocity is 1. 7 meters per second.

Equations for Speed and Velocity • v = d t • d = v t • t = d v • You can replace the s(speed) in the triangle for v(velocity)

Calculating Average Speed / Velocity • d= distance • v= speed / velocity • t= time

Sample Speed / Velocity Problems • A car travels a distance of 16 m in 1. 8 seconds. What is it’s speed? • d = 16 m • t = 1. 8 s • v = ? • v = d t • v = 16 m 1. 8 s v = 8. 89 m/s

Sample Speed / Velocity Problems • Sound travels at a speed of 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for the sound to reach you? • • v = 330 m/s d = 1 km t = ? t = d v t = 1 km 330 m/s You must change the km to m t = 1000 m Kids Haven’t Died By Doing Crazy Metric 330 m/s t = 3. 03 s

Practice Problems • 1. Calculate the speed of a dog running through a field if he is covering 23. 7 meters in 54 seconds. • 2. If a cross country runner covers a distance of 347 meters in 134 seconds what is her speed? • 3. What is the speed of a baseball that travels 49 meters in 2. 4 seconds?

Practice Problems 4. What is the speed of a horse in meters per second that runs a distance of 1. 2 miles in 2. 4 minutes? • • 5. Calculate the velocity of a car that travels 556 kilometers northeast in 3. 4 hours. Leave your answer in kilometers per hour. 6. If the distance covered by a jogger is 2, 541 meters through the park and the time it took to cover that distance was 43. 6 minutes, what was the speed of the jogger?

Practice Problems • 7. Which object has a greater velocity, a ball rolling down a 3. 4 meter hill in six seconds or a fish swimming upstream and covering 5. 4 meters in 0. 4 minutes? • 8. If Seneca decides to walk across town to a store that is . 95 kilometers away and she has only 25 minutes to get there, what speed does she need to maintain to arrive on time? • 9. If a projectile flies north 387 meters in 5. 8 seconds, what is its velocity? • 10. Calculate the velocity of a mountain climber if that climber is moving northeast at a pace of 1. 6 km in 1. 4 hours? Give your answer in the SI unit for velocity.

Acceleration

What is Acceleration? • • The rate of change of velocity. Car commercial 0 to 60 mph in 10 seconds. Speeding up The amount of change of velocity in a time interval.

Acceleration • The rate at which velocity changes • Acceleration is: – Increasing speed – Decreasing speed – Changing direction

How do you measure a change? • The water was at 50 m and it rose to 100 m. What is the change? • We started at 9: 00 am and the class was over at 11: 00 am. What is the change? • The dog grew from 8 lbs to 15 lbs. What is the change? • We had 20 gallons, and now we have 5. What is the change?

Increasing speed • Increase in speed = increase in acceleration • Ex—a car moving from a stopped position

Decreasing speed • Decrease in speed = deceleration (negative acceleration) • Ex– a car decelerates as it stops at a red light

Changing direction • Any change in direction is considered acceleration, even if the object’s speed remains constant • Ex– a Ferris wheel accelerates because it moves in a circle (changes direction). – Its speed is constant

Calculating Acceleration • Calculate the change in velocity during each unit of time • Acceleration = final velocity – initial velocity final time – initial time OR change in velocity (speed) time it took for change

How to Calculate Acceleration? Dmeans “change in”

How do you calculate Δv? • The change in velocity = the final velocity – the initial velocity. Δv = vf – vi • You are stopped at a red light. When it turns green, you speed up to 45 m/s. What is your change in velocity? vi = 0 m/s vf = 45 m/s Δv = ? Δv = vf-vi = 45 m/s- 0 m/s = 45 m/s

• Velocity is measured in meters/second • Acceleration is measured in meters per second or m/s 2 • Acceleration = 22 m/s – 4 m/s 3 s • A= 18 m/s 3 s • A = 6 m/s/s or 6 m/s 2

Let’s Practice with some Problems • A car’s velocity changes from 0 m/s to 30 m/s in 10 seconds. Calculate the car’s average acceleration. • Acceleration = final velocity – initial velocity change in time • A = 30 m/s – 0 m/s 10 s a = 30 m/s 10 s a = 3 m/s/s or 3 m/s 2

Practice Problem • In 2. 5 s a car increases its speed from 60 km/h to 65 km/h while a bicycle goes from rest to 5 km/h. • Which undergoes the greater acceleration? • What is the acceleration of each vehicle?

Answer : A = ending speed – initial speed time interval • Car’s acceleration: • a= 65 km/h – 60 km/h = 5 km/h = 2 km/h/s time interval 2. 5 s • Bicycle’s acceleration : • A = 5 km/h – 0 km/h = 5 km/h = 2 km/h/s 2. 5 s

What is negative acceleration? Also known as DECELERATION. The negative rate of change of velocity. Slowing down. The amount of negative change of velocity in a time interval. • Ex: • 10 m/s – 25 m/s = - 15 m/s = - 3 m/s/s or – 3 m/s 2 5 s • •