UNIT 5 RELATIONSHIPS AMONG FORMS OF ENERGY 8

UNIT 5 RELATIONSHIPS AMONG FORMS OF ENERGY 8 TH GRADE MIDDLE SCHOOL SCIENCE UNION TOWNSHIP SCHOOL DISTRICT

SPEED, VELOCITY AND ACCELERATION Speed, velocity and acceleration describe how an objects position and motion change through time. Rates measure change in something over a length of time.

WHAT IS SPEED? Speed - A measure of the distance an object travels per unit of time. How could we increase an objects speed?

INCREASING AN OBJECT’S SPEED • By increasing the distance the object travels in the same time. Or • By decreasing the time it takes for an object to travel the same distance.

Speed (S) = distance object travels time it takes to travel distance CALCULATING SPEED s=d t Measuring Distance Time Speed Metric Unit meter, kilometer, centimeter seconds, minutes, hours Meter per second Kilometer per hour Centimeter per minute Abbreviation m, km, cm s, min. , h m/s km/h cm/min.

STEPS TO COMPLETING A SPEED FORMULA STEP 1 Write the formula STEP 2 Plug in the information that you are given STEP 3 Solve the answer STEP 4 Add your units

PRACTICE Calculate the speed of a car going 80 meters in 20 seconds.

PRACTICE A girl runs 25 meters in 10 seconds. What is her speed?

CALCULATING SPEED If you know any two of the variables, you can calculate the missing variable.

PRACTICE A girl cycles for 3 hours at a speed of 40 km/h. What distance did she travel?

IS THEIR VELOCITY THE SAME? NO – they are both walking the same speed because the arrow’s are the same length, however their direction is different therefore the velocity is NOT the same

WHAT IS THE DIFFERENCE BETWEEN SPEED AND VELOCITY? Speed deals with the distance traveled over an amount of time. Velocity deals with the distance traveled over an amount of time in a specific direction. • The length of the arrow indicates the objects

STEPS TO COMPLETING A VELOCITY FORMULA STEP 1 Write the formula STEP 2 Plug in the information that you are given STEP 3 Solve the answer STEP 4 Add your units STEP 5 Add your direction

PRACTICE It takes Francisco 15 minutes to ride his bicycle 4 km, which is the distance from home to school. What is his velocity? Round to the nearest tenth.

PRACTICE It took Mrs. West 30 minutes to jog 4 miles toward her house. What is Mrs. West’s velocity? Round to the nearest tenth.

ANIL CYCLED FROM HIS HOME TO THE PARK AND BACK HOME. BELOW IS A DISTANCE-TIME GRAPH FOR ANIL’S COMPLETE JOURNEY. At what time did Anil leave home? _____________ How long did it take Anil to get to the park? __________ What is the distance from Anil’s home to the park? ____________ What was Anil’s velocity when traveling to the park? ___________ At what rate did Anil travel to the park? Constant Increasing Velocity Decreasing Velocity

ANIL CYCLED FROM HIS HOME TO THE PARK AND BACK HOME. BELOW IS A DISTANCE-TIME GRAPH FOR ANIL’S COMPLETE JOURNEY. How many minutes did Anil stay in the park? _____________ What was Anil doing between 9: 45 and 10: 05? ____________ In each blank graph on your paper draw a line for: 1. constant velocity 2. an object at rest 3. increasing speed 4. decreasing speed CHALLENGE: Calculate the average speed for Anil’s entire trip.

Andrew left home at 12 noon to go for a bike ride. The travel graph represents Andrew’s journey. • How long did it take Andrew to get to the park? • How far did he travel to get to the park? • What was Andrew’s average velocity when traveling to the park? • How long did he stop on his way to the park? • Calculate Andrew’s velocity for the entire trip.

Gen. Ed. Sara takes a 40 minute bus ride from her home to her grandparents’ house, which is 8 km away. What is the velocity of the bus? John ran the 40 meter dash in 3. 5 seconds. What was John’s speed? A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s acceleration?

Gen Ed. How far can you get away from your little brother with the squirt gun filled with paint if you can travel at 3 m/s and you have 15 seconds before he sees you? You need to get to class, 200 m away, and you can only walk in the hallways at a speed of about 1. 5 m/s (if you run any faster, you will get detention!). How much time will it take to get to your class?

• • Honors Sara takes a 40 minute bus ride from her home to her grandparents’ house, which is 8 km away. What is the velocity of the bus? John ran the 40 meter dash in 3. 5 seconds. What was John’s speed? A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s acceleration? How far can you get away from your little brother with the squirt gun filled with paint if you can travel at 3 m/s and you have 15 seconds before he sees you?

Honors • You need to get to class, 200 m away, and you can only walk in the hallways at a speed of about 1. 5 m/s (if you run any faster, you will get detention!). How much time will it take to get to your class? • Kelly left school and walked to her friend’s house in 10 minutes, which was 0. 5 km away. She stayed at her friends house for 15 minutes and then walked to her house 2 km away, which took 25 minutes. What was Kelly’s AVERAGE speed for this trip? • The puppy ran around the block (. 25 km) in 3 minutes. What is the speed the puppy ran in meters per second? Round to the nearest tenth.

ACCELERATION § A measure of the change in velocity during a period of time. §An object accelerates when its velocity changes as a result of: §Increasing speed §Decreasing speed §Change in direction (even if an object is traveling at a constant speed)

CALCULATING ACCELERATION

A BICYCLIST STARTED FROM REST ALONG A STRAIGHT PATH. AFTER 5 S, HIS SPEED WAS 8 M/S. WHAT WAS HIS ACCELERATION DURING THE TIME?

AFTER 3. 0 S, MOHAMMED WAS RUNNING AT 1. 2 M/S ON A STRAIGHT PATH HEADED EAST. AFTER 7. 0 S, HE WAS RUNNING AT 2. 0 M/S. WHAT WAS HIS ACCELERATION?